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Partial Denture FAYAD

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Partial Denture FAYAD Powered By Docstoc
					                2010
PARTIAL DENTURE THEORY
           AND PRACTICE




                MOSTAFA FAYAD
                Assistant Lecture of
                Removable Prosthodontic
                                                           OBJECTIVES AND CLASSIFICATION




        OBJECTIVES AND CLASSIFICATION OF PARTIAL DENTURES

                                TERMINOLOGY
• Prosthesis: Is an artificial replacement of an absent part of the human body.

• Prosthetics: The art and science of supplying an artificial replacement for
     missing parts of the human body.

• Appliance used only for device worn by patient in course of treatment. e.g.
     orthodontic appliance and splint

• Prosthodontics: The branch of dentistry pertaining to the restoration and
     maintenance of oral functions, comfort, appearance, and health of the patient
     by the restoration of natural teeth and/or the replacement of missing teeth
     and contiguous oral and maxillofacial tissue with an artificial substitute.

• Dentulous Patients: Patients having a complete set of natural teeth.

• Edentulous Patients: Patients having all their teeth missing.

• Partially Edentulous Patient: Patients having one or more but not their entire
     natural teeth missing.

• Removable Partial Denture (RPD): An appliance that restores one or more but
     not all of the missing natural teeth and associated oral structures for partially
     edentulous patients.

•        Abutment: A tooth, a portion of a tooth, or that portion of a dental
     implant that serves to support and/or retain prosthesis.

• Free End Edentulous Area (Distal extension edentulous area): An edentulous
     area, which has an abutment tooth on one side only.

• Bounded Edentulous Area: An edentulous area, which has an abutment tooth
    on each end.
• Dental cast: a positive life size reproduction of a part or parts of the oral
     cavity.

     The word cast is preferable than word model which used only for
           demonstration




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                                                         OBJECTIVES AND CLASSIFICATION




Andrews Bridge
      The combination of a fixed dental prosthesis incorporating a bar with a
  removable dental prosthesis that replaces teeth with the bar area, usually
  used for edentulous anterior spaces. The vertical walls of the bar may
  provide retention for the removable component. By James Andrews.
Gillett Bridge
      Eponym for a partial removable dental prosthesis utilizing a Gillett clasp
  system, which was composed of an occlusal rest notched deeply into the
  occlusal axial surface with a gingivally placed groove and a circumferential
  clasp for retention. The occlusal rest was custom made in a cast restoration.
MORA Device
      Acronym for mandibular orthopedic repositioning appliance, a type
  of removable dental prosthesis with a modification to the occlusal surfaces
  used with the goal of repositioning.
Angle of Gingival Convergence
      According to Schneider, the angle of gingival convergence is located
  apical to the height of contour on the abutment tooth. It can be identified by
  viewing the angle formed by the tooth surfaces gingival to the survey line
  and the analyzing rod or undercut gauge in a surveyor as it contacts the
  height of contour.
Continuous Gum Denture
      An artificial denture consisting of porcelain teeth and tinted porcelain
  denture base material fused to a platinum base.
Fulcrum Line
      It is an imaginary line, connecting occlusal rests, around which a partial
  removable dental prosthesis tend to rotate under masticatory forces. The
  determinants for the fulcrum line are usually the cross arch occlusal rests
  located adjacent to the tissue borne components.
Semi precision Rest
      A rigid metallic extension of a fixed or removable dental prosthesis that
  fits into an intracoronal preparation in a cast restoration.


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                                                       OBJECTIVES AND CLASSIFICATION




Nesbit Prosthesis
      Eponym for a unilateral partial removable dental prosthesis design, that
  De. Nesbit introduced in 1918.
Resilient Attachments
      An attachment designed to give a tooth borne/soft tissue borne
  removable dental prosthesis sufficient mechanical flexion, to withstand the
  variations in seating of the prosthesis due to deformation of the mucosa and
  underlying tissues without placing excessive stress on the abutments.


 CONSEQUENCES OF TOOTH LOSS
 1- A loss of ridge volume—both height and width—can be expected
      Bone loss is greater in the mandible than the maxilla, more pronounced
 posteriorly than anteriorly, and it produces a broader mandibular arch while
 constricting the maxillary arch.
 2- Alteration in the oral mucosa
      The attached gingiva of the alveolar bone can be replaced with less
 keratinized oral mucosa, which is more readily traumatized.
 3- Aesthetic impact
      Facial features can change Secondary to altered lip support and/or
 reduced facial height as a result of a reduction in occlusal vertical dimension.
4- Reduction in masticatory efficiency
      It is the ability to reduce food to a certain size in a given time frame. It
has been shown that there is a strong correlation between masticatory
efficiency and the number of occluding teeth in dentate individuals.
5.T.M.J.dysfunction
6. Tipping, migration, rotation and superimposition of remaining teeth.
7.Altered speech




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                                                        OBJECTIVES AND CLASSIFICATION




 Partial Dentures:
        Partial dentures are appliances restoring one or more but not the whole
 set of natural teeth . These Appliances maybe in form of:
 I-         Fixed partial prosthesis ( bridge ):
        An appliance which restores one or more missing teeth it is permanently
 cemented to the neighboring natural teeth and cannot be removed by the
 patient.


 II-        Removable partial prosthesis:
        An appliance which restores missing teeth and the associated oral
 structures for a partially edentulous patient " it can be removed by the patient .
 Removable partial dentures may restore :
 (a)    Bounded edentulous area : which has an abutment tooth on each end.
 (b)    Free end edentulous area : which has an abutment tooth on one side
 only . Partial dentures restoring free end cases are called distal- extension
 partial dentures.


 III- Partial over dentures : Partial over dentures are removable partial
      dentures that are constructed to overly and gain additional support
      from either :
 Natural teeth that are reduced in height and contour or :
 Implants inserted in the edentulous areas .


      IV-   Removable partial Dentures for Maxillo facial Defects :
      These are removable prostheses restoring tissue defects which are
either developmentally or traumatically acquired. They are usually
retained by clasps on the remaining natural teeth.




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                                                          OBJECTIVES AND CLASSIFICATION




Types of removable partial dentures :
( 1 ) Unilateral partial dentures : Partial dentures which restore teeth on one
side of the arch without being extended to the opposite side
( 2 ) Bilateral partial dentures : partial dentures restoring missing teeth and
extended on both sides of dental arch .
According to retention to natural teeth
a- Extra coronal retention
b- Intracranial retention
According to material
-Metallic       - acrylic    -flexible




OBJECTIVES OF REMOVABLE PARTIAL DENTURES


  1- Preservation of the Remaining Tissues:
The primary purpose of RPD is the preservation of the health of the remaining
tissues.
             A- Preservation of the health of the remaining teeth.
             The loss of teeth leads to migration, tilting or drifting of the
           remaining natural teeth into the edentulous spaces (Fig.1-3), such
           movements leads to unequal distribution of load on the remaining
           teeth. In addition to food impaction in the interstitial spaces leading to
           caries and /or gingivitis.


             B- Prevention of muscles and TMJ Dysfunction.
                     Absence or movements of posterior teeth may cause:
                   A- Changes in the pattern of mandibular closure (Fig.1-4).
                   B- Change in the vertical and horizontal relations of the
           mandible and maxilla. Consequently muscles and TMJ Dysfunction
           may arise.



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                                                       OBJECTIVES AND CLASSIFICATION




             C-Preservation of the residual ridge.
               By preventing rapid bone resorption which may happen due to
           lack of function.


             D-Preservation of the tongue contour and space.
2 Restore the Continuity of the Dental Arch to Improve Masticatory
Function:
     A reduction of the number of teeth leads to a decrease in the chewing
efficiency and greater effort on the digestive organs leading to digestive
disorders, accordingly replacing lost teeth will greatly improve the chewing
capability of the patients, distribute the load over the entire arch and improve
the balance over the whole masticatory system.


3- Improvement of Esthetics, and Providing Support to the Paraoral
Muscles, Lips and Cheeks:
     Teeth and the alveolar ridge give support to the musculature of the lips
and cheeks. Non-replacement of the missing teeth gives the patient a senile
appearance characterized by nose-chin approximation and wrinkles around
the lips. Missing teeth can be replaced with predictable results using partial
denture.


4- Restoration of Impaired speech:
     Anterior teeth play an essential role in phonetics, particularly in the
production of labio and linguo-dental sound. Loss or wrong position of
anterior teeth and subsequent alveolar ridge resorption can result in phonetic
impairment.
Proper replacement of artificial teeth in relation to the lip، tongue and alveolar
ridge، also the proper contouring of dentures help in restoration of speech
defects.




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                                                     OBJECTIVES AND CLASSIFICATION




5- Enhance psychological comfort:
      Partial dentures should restore and correct the appearance for the
psychological benefits of the patient, by providing socially acceptable
esthetics. A comfortable prosthesis will encourage and help in patient
rehabilitation .



 INDICATIONS FOR REMOVABLE PARTIAL DENTURES
   1. No abutment tooth posterior to edentulous space (Free end edentulous
      area)).
   2. After recent extraction, usually done only to improve esthetics, or for
      patient satisfaction.
   3. Long edentulous bounded span, too extensive for fixed restoration.
   4. Periodontally weak teeth not sufficiently sound to support fixed- partial
      denture.
   5. With excessive loss of residual bone, the use of labial flange or need to
      restore lost tissues.
   6. Need of bilateral bracing (cross arch stabilization).after periodontal
      diseases treatment ,fixed prosthesis provide only antero-posterior
      stabilization only not mediolateral .
  7. Enhancing esthetics in anterior region, by the use of translucent
     artificial teeth instead of dull fixed partial denture pontic.
  8. Young age (less than 17 years).
   9. Geriatric patients
  10. Immediate replacement.
  11. Economic considerations, attitude and desire of the patient.
  12. Physical problems.
  13. Unfavorable maxillo-mandibular relation.


 Contraindication
      1- Large tongue.
      2- Mentally retarded.
      3- Poor oral hygiene.


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ADVANTAGES OF REMOVABLE PARTIAL DENTURE OVER FIXED
PARTIAL DENTURE:
  1- They can be constructed for any case whilst fixed P.D. are confined to
     short spans bounded by healthy teeth and with a normal occlusion.
  2- Cheaper than fixed partial denture.
  3- They are more easily cleaned.
  4- They are more easily repaired.
  5- No tooth reduction is required.
Disadvantages of a Removable Partial Denture:
1- It can cause caries: by harboring food debris in close contact with the
natural teeth a partial denture may promote caries. This will depend on
several factors, chief of which are:
     a) The age of the patient, up to the age of 25 years caries susceptibility is
     greatest, there after it tends to decrease.
     b) The oral hygiene of the patient.
     c) The design of the denture: this is all important because well designed
     dentures will cause for less damage to the mouth than those of through
     less design.
2- It can damage the supporting tissues of the teeth: removable partial
dentures may cause damage to the gum margins by:
    a) Fitting too closely into the gingival tissues: through and causing
    mechanical injury to it.
    b) Allowing food to pack down between the denture and the teeth.
3- It may loosen the natural teeth by leverage: clasps which grip the teeth
too tightly or indirect retainers which are badly placed may cause excessive
stresses to be induced in the natural teeth .
4- It can cause traumatic damage to the palate.
5. Clasps can be unesthetic, particularly when they are placed on visible tooth
surfaces.




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                                                        OBJECTIVES AND CLASSIFICATION




  HAZARDS OF IMPROPERLY DESIGNED PARTIAL DENTURES
        An improperly designed and constructed partial denture may adversely
  affect the tissues in the following manner:
  1- Stagnation of food around component parts of partial denture in contact
  with tooth surfaces that are not readily cleaned causes tooth decay .
   2- Induce stresses on abutment teeth and tissues. If these stresses exceed the
  physiologic limits of tissue tolerance, pathologic and destructive changes may
  occur:
     a) Excessive stresses on abutment teeth cause periodontal membrane
      destruction, pocket formation, mobility, and even loss of these teeth.
     b) Inflammation, ulceration and gingival recession may occur due to
      excessive stresses and undue coverage of tissues with the restoration.
      Inadequate denture support due to inadequate stoppers, this causes
      displacement of the restoration towards the tissues causing gum stripping.
     c) Stresses may also cause bone resorption and loss of the bony foundation
      necessary to support the prosthesis.
 3- Improper occlusion of teeth or the presence of premature contact may cause
        T.M.J. disorders.


      PHASES OF PARTIAL DENTURE SERVICE

1- Education of patient: the process of informing a patient about a health matter
 to secure informed consent, patient cooperation, and a high level of patient
 compliance. Patient education should begin at the initial contact with the
 patient and continue throughout treatment.
2- Diagnosis, treatment planning, design, treatment sequencing, and mouth
 preparation.
3- Support for Distal Extension Denture Bases.


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                                                         OBJECTIVES AND CLASSIFICATION




4- Establishment and Verification of Occlusal Relations and Tooth
 Arrangements.
5- Initial Placement Procedures.
6- Periodic Recall.




         REASONS FOR FAILURE OF CLASP-RETAINED P.D.
Diagnosis and treatment planning
1. Inadequate diagnosis
2. Failure to use a surveyor or to use a surveyor properly during treatment
  planning
Mouth preparation procedures
1. Failure to properly sequence mouth preparation procedures
2. Inadequate mouth preparations, usually resulting from insufficient planning of
  the design of the partial denture or failure to determine that mouth preparations
  have been properly accomplished
3. Failure to return supporting tissue to optimum health before impression
  procedures
4. Inadequate impressions of hard and soft tissue
Design of the framework
1. Failure to use properly located and sized rests
2. Flexible or incorrectly located major and minor connectors
3. Incorrect use of clasp designs
4. Use of cast clasps that have too little flexibility, are too broad in tooth
  coverage, and have too little consideration for esthetics
Laboratory procedures
1. Problems in master cast preparation
a. Inaccurate impression
b. Poor cast-forming procedures


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                                                          OBJECTIVES AND CLASSIFICATION




c. Incompatible impression materials and gypsum products
2. Failure to provide the technician with a specific design and necessary
  information to enable the technician to execute the design
3. Failure of the technician to follow the design and written instructions
Support for denture bases
1. Inadequate coverage of basal seat tissue
2. Failure to record basal seat tissue in a supporting form
Occlusion
1. Failure to develop a harmonious occlusion
2. Failure to use compatible materials for opposing occlusal surfaces
Patient-dentist relationship
1. Failure of the dentist to provide adequate dental health care information,
  including care and use of prosthesis
2. Failure of the dentist to provide recall opportunities on a periodic basis
3. Failure of the patient to exercise a dental health care regimen and respond to
  recall


          CLASSIFICATION OF PARTIALLY
              EDENTULOUS ARCHES


  Need for classification:
 1- To differentiate between different partial denture.
 2- It facilities writing or speaking about partial denture designs and referral or
 prescription writing to the laboratory thus facilitating communication.
 3- To formulate good treatment plane.
 4- To anticipate difficulties commonly to occur for each class.
 Requirements of an Acceptable Classification:
 Classifications are important to facilitate communication between the dentist
 and the laboratory technician. Acceptable classification should satisfy the
 following requirements:
    1.Permit immediate visualization of the type of partially edentulous arch.
    2.Permit immediate differentiation between bounded and free extension
    partial dentures.
    3. It should be universally accepted.


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                                                          OBJECTIVES AND CLASSIFICATION




  4. Serve as guide to design used.
Classifications
       Several methods of classification based on various factors have
been proposed.
       A- Classification According to the Extent of the Removable
Partial Denture:


1- Unilateral RPD (Removable Bridge): which restore missing teeth on one
   side of the arch without being extended to the other side. This unilateral
   design provides least amount of tooth preparation and least amount of tooth
   and soft tissue contact.
         For unilateral removable partial denture to be successful:
                      1. clinical crown of abutment tooth must be long enough to
                            resist rotational forces.
                      2. The buccal and lingual surfaces of the abutment tooth
                            must be parallel to resist tipping forces.
                      3. Retentive undercuts should be available on both the
                            buccal and lingual surfaces of each abutment.
       * Unilateral removable partial denture should be used with caution. as
the chance of the denture becoming dislodged and aspirated is too great.


       Bilateral RPD: which restore missing teeth and extended on both sides
of the dental arch.


     B- Cummer's classification :
              This classification mainly based upon various the position of
       the direct patner of the finished restoration . The direct retainer
       may be diagonally, diametric, unilaterally or multilaterally placed.
       This classification describes the restored rather than the unrestored
       arch, so it is of line value because it follows denture design .


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                                                     OBJECTIVES AND CLASSIFICATION




    C - Bailyn classification :
              Bailyn,s classification is based on the support afforded to the
        denture by the tissues . the restorations may be :
            o Tissue born prosthesis : the denture is enterily supported by
               the mucosa and the underlying bone .
            o Tooth –born prosthesis : the denture is entirely supported by
               abutment teeth .
            o Tooth –tissue supported prosthesis : the denture is supported
               bu both abutment teeth and moucosa.
        D- Fridman's classification :
   Fridman classified partial dentures in to :
   Group A – for anterior restoration
   Group B- For bounded posterior restoration
   Group C- For posterior free end restoration (c= cantilever) .


E - Osborne and Lammie (1974)
   • Class I: Denture supported by mucosa and underlying bone
   • Class II: Denture supported by teeth
   • Class III: Denture supported by a combination of mucosa and tooth-
   borne means.
   • Class IV: Denture supported by implants.


F.Beckett and Wilson
       Class I: Bounded saddle and the abutment can’t support the saddle
   • Class II: Free end saddle
             A. Tooth and tissue support
              B. Tissue support
   • Class III: Bounded saddle and the abutment can support the saddle



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                                                         OBJECTIVES AND CLASSIFICATION




 Skinner's Classification
 He introduced the classification in 1959. He said that about 1,31,072
 combinations of partially edentulous arches are possible.
 His classification is based on the relation of the edentulous arches to the
 abutment teeth.
 • Class I: Abutment teeth are present anterior and posterior to the edentulous
 space. It may be unilateral or bilateral.
 •   Class II: All the teeth are present posterior to the denture base which
 functions as a partial denture unit. It may be unilateral or bilateral.
 •   Class III: All abutment teeth are anterior to the denture base which
 functions as a partial denture unit. It may be unilateral or bilateral.
 • Class IV: Denture bases are located anterior and posterior to the remaining
 teeth, and these may be unilateral or bilateral.
 • Class V: Abutment teeth are unilateral in relation to the denture base, and
 these may be unilateral or bilateral.




 H- Kennedy's Classification:
      Dr. Edward Kennedy proposed this classification in 1923. This is the
most popular classification. It is based on locations and number of
edentulous areas.


 Class I: Bilateral edentulous areas (free-end saddles) located posterior to the
 remaining natural teeth.72%


 Class II: A unilateral edentulous area (free-end saddle) located posterior to
 the remaining natural teeth.14%


 Class III: A unilateral edentulous area with natural teeth remaining both
 anterior and posterior to it.8,5%




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                                                         OBJECTIVES AND CLASSIFICATION




Class IV: A single, but bilateral (crossing the midline ), edentulous area
located anterior to the remaining natural teeth.3%

  Applegate later added two classes
  Class V: A unilateral edentulous area with natural teeth remaining both
  anterior and posterior to it but the anterior abutment is not suitable for
  support.
  Class VI: A unilateral edentulous area with natural teeth remaining both
  anterior and posterior to it with abutments capable for total support.


  FISET'S ADDITIONS
  Class VII A partially edentulous situation in which all remaining natural
  teeth are located on one side of the arch, or of the median line


  Class VIII A partially edentulous situation in which all remaining natural
  teeth are located in one anterior corner of the arch


  Class IX A partially edentulous situation in which functional and cosmetic
  requirements or the magnitude of the interocclusal distance require the use
  of a telescoped prosthesis (partial or complete).The remaining teeth are
  capable of total or partial support for the prosthesis.


  Class X A partially edentulous situation in which the remaining teeth are
  incapable of providing any support. If the teeth are kept to maintain
  alveolus integrity, the arch must be restored with an OVERDENTURE
  which is a complete denture supported primarily by the denture foundation
  area




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                                                          OBJECTIVES AND CLASSIFICATION




       The numeric sequence of the classification system is based on the
 frequency of occurrence of each class. Class I being the most common While
 class IV is the least common. This classification was then modified by
 Applegate .
       Why a unilateral edentulous area is considered as class II?
       Because it include features of both class I and class III especially if
 modification is present.


    Advantages
    1- It is the most widely used method of classification of the partially
    edentulous arches.
    2- It is simple and can be easily applied to nearly all partially
    edentulous bases.
    3- It permits immediate visualization of the partially edentulous arch
    and permits a logical approach to the problems of design.

       Applegate has provided the following eight rules governing the
application of the Kennedy system.
       Applegate's Rules for Applying the Kennedy Classification:
       Rule (1) : Classification should follow rather than precede any
extraction of teeth that might alter the original classification.
       Rule (2) : If the third molar is missing and not to be replaced, it is not
considered in the classification.
       Rule (3) : If a third molar is present and is to be used as an abutment, it
is considered in the classification.
       Rule (4) : If a second molar is missing and is not to be replaced (that is,
the opposing second molar is also missing and is not to be replaced ), it is not
considered in the classification.
       Rule (5) : The most posterior edentulous area or areas always determine
the classification.



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                                                           OBJECTIVES AND CLASSIFICATION




       Rule (6) : Edentulous areas other than those determining the classification
are referred to as modification spaces and are designated by their number.
       Rule (7) : The extent of the modification is not considered, only the
number of additional edentulous areas.
       Rule (8) : There can be no modification areas in Class IV arches. Any
edentulous area lying posterior to the "single bilateral area crossing the
midline" would instead determine the classification.
       Class IV Partial dentures especially those having long edentulous areas
are considered mesial extension bases. They require the same denture design
principles as class I partial dentures.




ACP classification system for partial edentulism J Prosthodont 2002;11:181-193.

          Prosthodontic Diagnostic Index ( PDI )
The American College of Prosthodontists (ACP) has developed a classification
system for partial edentulism based on diagnostic findings. This classification
system is based on diagnostic findings. Four categories of partial edentulism
are defined, Class I to Class IV, with Class I representing an uncomplicated
clinical situation and class IV representing a complex clinical situation. Each
class is differentiated by specific diagnostic criteria.
          Diagnostic Criteria
     1. Location and extent of the edentulous area(s)
    2. Condition of abutments
    3. Occlusion
    4. Residual ridge characteristics.


    Class I
          This class is characterized by ideal or minimal compromise in the
    location and extent of edentulous area (which is confined to a single arch),




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                                                     OBJECTIVES AND CLASSIFICATION




abutment conditions, occlusal characteristics, and residual ridge conditions.
All 4 of the diagnostic criteria are favorable.
1. The location and extent of the edentulous area are ideal or minimally
compromised:
● The edentulous area is confined to a single arch.
● The edentulous area does not compromise the physiologic support of the
abutments.
● The edentulous area may include any anterior maxillary span that does
not exceed 2 incisors, any anterior mandibular span that does not exceed
4 missing incisors, or any posterior span that does not exceed 2 premolars
or 1 premolar and 1 molar.
2. The abutment condition is ideal or minimally compromised, with no
need for preprosthetic therapy.
3. The occlusion is ideal or minimally compromised, with no need for
preprosthetic therapy; maxillomandibular relationship: Class I molar and
jaw relationships.
4. Residual ridge morphology conforms to the Class I complete
edentulism description.


Class II
     This class is characterized by moderately compromised location and
extent of edentulous areas in both arches, abutment conditions requiring
localized adjunctive therapy, occlusal characteristics requiring localized
adjunctive therapy, and residual ridge conditions.
1. The location and extent of the edentulous area are moderately
compromised:
● Edentulous areas may exist in 1 or both arches The edentulous areas do
not compromise the physiologic support of the abutments.
● Edentulous areas may include any anterior maxillary span that does not
exceed 2 incisors, any anterior mandibular span that does not exceed 4
incisors, any posterior span (maxillary or mandibular) that does not exceed


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                                                     OBJECTIVES AND CLASSIFICATION




2 premolars, or 1 premolar and 1 molar or any missing canine (maxillary or
mandibular).
2. Condition of the abutments is moderately compromised:
● Abutments in 1 or 2 sextants have insufficient tooth structure to retain or
support intracoronal or extracoronal restorations.
● Abutments in 1 or 2 sextants require localized adjunctive therapy.
3. Occlusion is moderately compromised:
● Occlusal correction requires localized adjunctive therapy.
● Maxillomandibular relationship: Class I molar and jaw relationships.
4. Residual ridge morphology conforms to the Class II complete
edentulism description.


Class III
  This class is characterized by substantially compromised location and
extent of edentulous areas in both arches, abutment condition requiring
substantial localized adjunctive therapy, occlusal characteristics requiring
reestablishment of the entire occlusion without a change in the occlusal
vertical dimension, and residual ridge condition.
1. The location and extent of the edentulous areas are substantially
compromised:
● Edentulous areas may be present in 1 or both arches.
● Edentulous areas compromise the physiologic support of the abutments.
● Edentulous areas may include any posterior maxillary or mandibular
edentulous area greater than 3 teeth or 2 molars, or anterior and posterior
edentulous areas of 3 or more teeth.
2. The condition of the abutments is moderately compromised:
● Abutments in 3 sextants have insufficient tooth structure to retain or
support intracoronal or extracoronal restorations.
● Abutments in 3 sextants require more substantial localized adjunctive
therapy (ie, periodontal, endodontic or orthodontic procedures).
● Abutments have a fair prognosis.


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                                                   OBJECTIVES AND CLASSIFICATION




3. Occlusion is substantially compromised:
● Requires reestablishment of the entire occlusal scheme without an
accompanying change in the occlusal vertical dimension.
● Maxillomandibular relationship: Class II molar and jaw relationships.
4. Residual ridge morphology conforms to the Class III complete
edentulism description.


Class IV
     This class is characterized by severely compromised location and
extent of edentulous areas with guarded prognosis, abutments requiring
extensive therapy, occlusion characteristics requiring reestablishment of
the occlusion with a change in the occlusal vertical dimension, and residual
ridge conditions.
1. The location and extent of the edentulous areas results in severe occlusal
compromise:
● Edentulous areas may be extensive and may occur in both arches.
● Edentulous areas compromise the physiologic support of the abutment
teeth to create a guarded prognosis.
● Edentulous areas include acquired or congenital maxillofacial defects.
● At least 1 edentulous area has a guarded prognosis.
2. Abutments are severely compromised:
● Abutments in 4 or more sextants have insufficient tooth structure to
retain or support intracoronal or extracoronal restorations.
● Abutments in 4 or more sextants require extensive localized adjunctive
therapy.
● Abutments have a guarded prognosis.
3. Occlusion is severely compromised:
● Reestablishment of the entire occlusal scheme, including changes in the
occlusal vertical dimension, is necessary.
● Maxillomandibular relationship: class II division 2 or Class III molar and
jaw relationships.


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                                                  OBJECTIVES AND CLASSIFICATION




4. Residual ridge morphology conforms to the class IV complete
edentulism description.
Other characteristics include severe manifestations of local or systemic
disease, including sequelae from oncologic treatment, maxillomandibular
dyskinesia and/or ataxia, and refractory patient (a patient who presents with
chronic complaints following appropriate therapy).




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                                                         OBJECTIVES AND CLASSIFICATION




Implant-Corrected Kennedy (ICK) Classification System for
Partially Edentulous Arches Journal of Prosthodontics 17 (2008) 502–5

Guidelines for the new classification system
          The new classification system will follow the Kennedy method with
the following guidelines:
(1) No edentulous space will be included in the classification if it will be
restored with an implant-supported fixed prosthesis.


(2) To avoid confusion, the maxillary arch is drawn as half circle facing up
and the mandibular arch as half circle facing down. The drawing will appear as
if looking directly at the patient; the right and left quadrants are reversed.


(3) The classification will always begin with the phrase "Implant-Corrected
Kennedy (class)," followed by the description of the classification. It can be
abbreviated as follows:
(i) ICK I, for Kennedy class I situations,
(ii) ICK II, for Kennedy class II situations,
(iii) ICK III, for Kennedy class III situations, and
(iv) ICK IV, for Kennedy class IV situations.


(4) The abbreviation “max” for maxillary and “man” for mandibular can
precede the classification. The word modification can be abbreviated as “mod.”


(5) Roman numerals will be used for the classification, and Arabic numerals
will be used for the number of modification spaces and implants.


(6) The tooth number using the American Dental Association (ADA) system is
used to give the number and exact position of the implant in the arch. (Note:
other tooth numbering systems such as F´ed´eration Dentaire Internationale
[FDI] can be used, as can the tooth name. The ADA system was used by the
authors because of familiarity).


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                                                                       OBJECTIVES AND CLASSIFICATION




                              Universal numbering system table



                                     Permanent Teeth



                 upper left                                      upper right



16   15     14   13   12      11   10    9     8     7      6     5       4    3      2    1



17   18     19   20   21      22   23    24    25    26     27    28      29   30     31   32



                 lower left                                      lower right




(7) The classification of any situation will be according to the following
order: main classification first,
          then the number of modification spaces,
          followed by the number of implants in parentheses according to their
position in the arch preceded by the number sign (#).


(8) The classification can be used either after implant placement to describe
any situation of RPD with implants, or before implant placement to indicate the
number and position of future implants with an RPD.


(9) A different name, ICK Classification System, is given to this classification
system to be differentiated from other partially edentulous arch classification
systems.




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                                           OBJECTIVES AND CLASSIFICATION




ICK I (#2, 15).                  ICK II mod 1 (#21, 26, 30).




                                 ICK III mod 3 (#23, 26).
ICK I (#2).




ICK I mod 3 (#18, 22, 28, 31).
                                 ICK IV (#6, 11)




ICK II (#2).




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                                                        OBJECTIVES AND CLASSIFICATION




Component Parts of removable partial dentures

    Denture bases.
    Artificial teeth .
        Supporting rests.
    Connectors: Major connectors
                   Minor connectors
    Retainers : Direct retainers
                   Indirect retainers
These components may provide one or more of the following functions:


 1-Support:
       a. The resistance of a denture to tissue ward movement.
       b. Adequate and wide distribution of the load to the teeth and mucosa.
 2- Retention: The resistance of a denture to vertical displacement force (to
        move away from its tissue foundation)).
 3- Indirect retention: The resistance of denture rotation away from the
        tissues about an axis.
 4- Bracing: The resistance of a denture to lateral forces.
 5- Reciprocation: The resistance of lateral forces on the abutment during
        insertion and removal of the removable partial denture .
        Reciprocation is required as the denture is being displaced occlusally
        whilst the bracing function, comes into play when the denture is fully
        seated.
 6- Stability: The resistance of a denture to tipping movement.
        Tipping movement: Vertical rotation around a line parallel to ridge crest
        (twisting of the denture base)




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                                                                          Denture Base


                    COMPONENT PARTS OF RPD

        Components of metallic removable partial dentures are all rigid, with
the exception of the flexible retentive clasp arm located in an undercut area for
retaining the restoration against dislodging forces.

The components of removable partial denture are:

 1.    One or More Denture Bases.             5.    Minor connectors.

 2.    Artificial teeth.                      6.    Direct retainers.

 3.    Supporting rests.                      7.    Indirect retainers.

 4.     Major connectors.

These Components May Provide One or More of the Following Functions:

1-Support: The resistance of a denture to tissue ward movement.

2- Retention: The resistance of a denture to vertical displacement force (to move
away from its tissue foundation).

3- Indirect retention: The resistance of denture rotation away from the tissues
about an axis.

4- Bracing: The resistance of a denture to lateral forces.

5- Reciprocation: The resistance of lateral forces on the abutment during insertion
and removal of the removable partial denture.

Reciprocation is required as the denture is being displaced occlusally whilst the
bracing function, comes into play when the denture is fully seated.

6- Stability: The resistance of a denture to tipping movement.

   Tipping movement: Vertical rotation around a line parallel to ridge crest
(twisting of the denture base)




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                                                                            Denture Base


                                   Denture Base
        The denture base is the part of the denture, which rests on the foundation
 tissues and to which artificial teeth are attached. The denture base helps in
 transferring occlusal stresses to the supporting oral structures.

 Types of Denture Bases

 1-     Bounded partial denture bases

        The bounded partial denture base covers an edentulous span between two
 abutment teeth.

 2- Free-end partial denture bases (distal-extension base)

        The base bounded by a natural tooth only on one side, while the other side is
 free. This type is sometimes called distal extension base.

 3- Bar type saddle

        In case of posterior bounded saddle, where esthetic is not important, a bar of
 metal is attached directly to the connector to form occlusal surface and no mucosal
 contact .

 Functions of the Denture Base

1. Carries the artificial teeth.

2. Transfers occlusal stresses to the supporting oral structures.

3. Provides support in distal-extension and long span bounded dentures.

 The snowshoe principle, which suggests that broad coverage furnishes the best
 support with the least load per unit area, is the principle of choice for providing
 maximum support. Therefore support should be the primary consideration in
 selecting, designing, and fabricating a distal extension partial denture base.
4. Provides denture retention for distal-extension dentures by physical means.



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                                                                             Denture Base


 5. Provides denture bracing against horizontal movement when extended to cover
   lateral borders of the ridge for distal-extension dentures.

 6. Provides stabilization against tipping of the distal-extension dentures (On the
   contra-lateral side).

 7. The denture base and the artificial teeth serve to prevent migration and over
   eruption of the remaining teeth.

 8.    Provide stimulation by massage of the underlying tissues of the residual ridge.
   Oral tissues placed under functional stress within their physiological tolerance
   maintain their form and tone better than similar tissues suffering from disuse.
 9. A the tooth-supported partial denture base that replaces anterior teeth must
   perform the following functions:
        (1) Provide desirable esthetics;
        (2) Support and retain the artificial teeth in such a way that they provide
            masticatory efficiency and assist in transferring occlusal forces directly to
            abutment teeth through rests;
      (3) prevent vertical and horizontal migration of remaining natural teeth;
      (4) Eliminate undesirable food traps (oral cleanliness);
      (5) Stimulate the underlying tissue.



   Requirements of an Ideal Denture Base Material

1- Accuracy of adaptation to the tissues، with minimal dimensional changes.

2- Sufficient strength in order to resist fracture and distortion.

3- Low specific gravity, i.e. light in weight in the mouth.

4- Biological acceptability, non-allergic and non-irritating surface capable of receiving
   and maintaining a good finish

5- Allow thermal conductivity necessary for tissue stimulation.




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                                                                           Denture Base


6- Can easily be kept clean.

7- Esthetic acceptability.

8- Potential for future relining.

9- Low initial cost.




   CRITERIA FOR SELECTION

   A.     NEED TO RELINE.

          1.      Tooth-mucosa borne partial dentures direct functional forces as
          pressure to the mucoosseous tissues. When resorptive changes occur, the
          base requires relining to maintain optimum support. Resin bases are
          easily relined.

          1.      In tooth borne partial dentures with long span bases, the base
          may require periodic relining to compensate for idiopathic or pressure
          induced resorptive changes

   B.     NEED TO RESTORE MISSING TISSUES. A resin base may be shaped
   and shaded to restore anatomic contour and esthetics.

   C.     LIMITED VERTICAL SPACE. When vertical space is limited, the
   minimal space may require a stronger metal base.

   D.     MAGNITUDE OF APPLIED FORCES. The anticipated occlusal forces
   may influence the choice of materials.

   E.     EASE OF ADJUSTMENT. Resin bases are more easily adjusted than
   metal bases.




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                                                                           Denture Base


Denture Base Material

I- Metallic denture bases

  Metallic denture bases are generally used in thinner sections than resin bases.
They are made in the form of metal plates having metal posts that allow for
mechanical attachment with the acrylic resin layer holding the artificial teeth.

  Metal such as chrome cobalt alloy, gold, or stainless steel is used. Chrome cobalt
alloy is the most commonly used alloy the material is used in cast form only. It
provides the needed rigidity for removable partial dentures even in thin section. It
has low specific gravity which is nearly half that of gold and provides high
resistance to corrosion.

   Advantages of Metal bases as compared to resin bases:

           1- Accuracy and Permanence of Form

              Denture bases fit more accurately to the underlying tissues. Accurate
           metal castings are not subject to distortion by the release of internal
           strains as are acrylic denture resins.

              The metal base provides an intimacy of contact that contributes
           considerably to the retention of denture prosthesis. (called interfacial
           surface tension).

              Additional posterior palatal seal may be eliminated entirely when a
           cast palate is used for a complete denture, as compared with the need for
           a definite post-dam when the palate is made of acrylic resin.

              Permanence of form of the cast base is also ensured because of its
           resistance to abrasion from denture cleaning agents.

       2- Comparative Tissue Response

                     Cast metal base contributes to the health of oral tissue when
           compared with an acrylic resin base. Perhaps some of the reasons for this


                                                                        Mostafa Fayad 5
                                                                   Denture Base


   are the greater density and the bacteriostatic activity contributed by
   ionization and oxidation of the metal base.

                Acrylic resin bases tend to accumulate mucinous deposits
   containing food particles and calcareous deposits.

3- Thermal Conductivity

                Cast metal base has Greater thermal conductivity, while
      denture acrylic resins have insulating properties.

4- Weight and Bulk

                Metal alloy may be cast much thinner than acrylic resin and
      still have adequate strength and rigidity. Cast gold must be given
      slightly more bulk to provide the same amount of rigidity but may still
      be made with less thickness than acrylic. less weight and bulk are
      possible when the denture bases are made of chrome or titanium
      alloys.

                an acrylic resin base may be preferable to the thinner metal
      base in (1) extreme loss of residual alveolar bone may make it
      necessary to add fullness to the denture base to restore normal facial
      contours and (2) to fill out the buccal vestibule to prevent food from
      being trapped in the vestibule beneath the denture.(3) Denture base
      contours for functional tongue and cheek contact can best be
      accomplished with acrylic resin.(4) acrylic resin bases may be
      contoured to provide ideal polished surfaces that contribute to the
      retention of the denture, restoration of facial contours, and prevention
      of the accumulation of food at denture borders.

   5- More hygienic as the fitting surface is polished and non-porous with
   less tendency for food accumulation.




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                                                                             Denture Base


            6- Stimulation to the underlying tissue so prevents some alveolar
            atrophy that would otherwise occur under a resin base and thereby would
            prolong the health of the tissue that it contacts.

            7- Disadvantages of Metal Bases

           1. Metal bases are difficult to rebase or reline when ridge resorption
               occurs.

           2. They are difficult to repair.

           3. The color of metal bases does not simulate the natural appearance or
               oral tissues.




Retentive post used with metal base.

Indication: 1- short span posterior tooth born 2- when maximum strength is required

              3- vertical height limited           4- significance anterior overlap

The choice of alloy is based on several factors:

(1) weighed advantages or disadvantages of the physical properties of the alloy;

(2) The dimensional accuracy with which the alloy can be cast and finished;

(3) The availability of the alloy;

(4) The versatility of the alloy; and

(5) The individual clinical observation and experiences with alloys in respect to
quality control and service to the patient.

A-Chrome cobalt alloy:

       It is used in cast form only, needs special investments and special casting
and polishing machine and high casting temperature (2400 f).


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                                                                       Denture Base


      Advantages:

          Accurate and rigid even in thin sections.

          Low specific gravity 7-9 gram/cm3 nearly 1/2 of that of gold.

          Highly polished surface.

          High resistance to corrosion and abrasion.

          Low density (weight), high modulus of elasticity (stiffness),

          Cheaper than gold..

          A low-fusing, chrome-cobalt alloy or gold alloy can be cast to
             wrought wire, and wrought-wire components may be soldered to
             either gold or chrome-cobalt alloys

B-Gold (type 4)

      Disadvantages in relation to chrome cobalt:

      1-Heavier than chrome cobalt (specific gravity 15 gm/ cm3).

      2- More rigid than acrylic resin but less than chrome cobalt. Modiolus of
      rigidity 14×106 P.S.I

      3- More expensive.

      Some times used for lower partial denture to help in retention due to more
      specific gravity (weight).

      The modulus of elasticity refers to stiffness of an alloy. Gold alloys have a
      modulus of elasticity approximately one half of that for chromium-cobalt
      alloys for similar uses.

             The greater stiffness of chromium-cobalt alloy is advantageous but
      at the same time offers disadvantages. The hardness of chromium-cobalt
      alloys presents advantages when Greater rigidity can be obtained with the


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                                                                  Denture Base


chromium-cobalt alloy in reduced sections in which cross-arch stabilization
is required, thereby eliminating an appreciable bulk of the framework. Its
greater rigidity is also an advantage when the greatest undercut that can be
found on an abutment tooth is in the nature of 0. 05 inch. A gold retentive
element would not be as efficient in retaining the restoration under such
conditions as would the chromium-cobalt clasp arm. The hardness of
chromium-cobalt alloys presents a disadvantage when a component of the
framework, such as a rest, is opposed by a natural tooth or by one that has
been restored. We have observed more wear of natural teeth opposed by
some of the various chromium-cobalt alloys as contrasted to the Type IV
gold alloys.

A high yield strength and a low modulus of elasticity produce higher
flexibility. The gold alloys are approximately twice as flexible as the
chromium cobalt alloys, which is a distinct advantage in the optimum
location of retentive elements of the framework in many instances. The
greater flexibility of the gold alloys usually permits location of the tips of
retainer arms in the gingival third of the abutment tooth.

The stiffness of the chromium-cobalt alloys can be overcome by

1- Including wrought-wire retentive elements in the framework.

2- The bulk of a retentive clasp arm for a removable partial denture is often
reduced for greater flexibility when chromium-cobalt alloys are used as
opposed to gold alloys. This, however, is inadvisable because the grain size
of the chromium-cobalt alloys is usually larger and is associated with a lower
proportional limit, and so a decrease in the bulk of chromium-cobalt cast
clasps increases the likelihood of fracture or permanent deformation.

   The retentive clasp arms for both alloys should be approximately the
same size, but the depth of undercut used for retention must be reduced by
one half when chromium-cobalt is the choice of alloys.



                                                               Mostafa Fayad 9
                                                                         Denture Base


       It has been observed that gold frameworks for removable partial dentures are
       more prone to produce uncomfortable galvanic shocks to abutment teeth
       restored with silver amalgam than frameworks made of chromium-cobalt
       alloy.

c- Stainless steel:

       It is used mainly in swaged form.

       The disadvantages of this type are;

       1-       Less accurate than chrome cobalt or gold

       2-       Less commonly used.

d- TI/AL/vanadiaum / e- Commercial pure titanium

       Commercially pure (CP) titanium and titanium in alloys containing
aluminum and vanadium, or palladium (Ti-0 Pd), should be considered potential
future materials for removable partial denture frameworks.

       Currently, when CP titanium is cast under dental conditions, the material
properties change dramatically. During the casting procedure, the high affinity of
the liquid metal for elements such as oxygen, nitrogen, and hydrogen results in their
incorporation from the atmosphere.

       The typical Young's modulus of elasticity of titanium alloy is half that of
chromium-cobalt and just slightly higher than type IV gold alloys. This would
require a different approach to clasp design than with chromium-cobalt alloys and
present some advantages. Wrought titanium alloy




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                                                                             Denture Base


II- Non-metallic, acrylic resin denture bases

Acrylic removable partial dentures are considered as temporary partial dentures. It
is made of acrylic denture base, artificial teeth and wrought wire clasps.

Advantages:

    1. Esthetically acrylic resin is satisfactory and looks better in the mouth due to
    its pink colour.

    2- Acrylic bases are light in weight.

    3- The material is easy to reline, rebase or repair.

    4- Needs simple processing procedures.

Disadvantages of resin base:

     1.       Resin bases are weak, brittle and are liable to fracture.

     2.       In order to attain enough strength, resin bases are made bulky

     3.       Acrylic bases have low thermal conductivity.

     4.       The fitting surface is porous and not polished which may lead to
       retention of soft food particles and plaque causing bad oral hygiene, bad
       odour and inflammation of the tissues.

 Indications of Acrylic removable partial dentures:

    1- When age and time factors may prohibit the construction of the definitive
    prosthesis.

    2- During the healing process after extraction until the permanent restoration is
    made.

    3- Cases with extreme bone loss. The presence of acrylic resin is necessary to
    restore the original contour of the ridge, giving more satisfactory results than
    metal bases.



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                                                                           Denture Base


    4- When cost is a prime requisite.

    5- Acrylic bases of temporary acrylic removable partial dentures.

    6- Immediate denture

    7- Transitional and interim denture

    8- Only few isolated teeth remaining.

Contraindications:

  1. Single tooth edentulous spaces.

  2. Where protrusive or lateral occlusal guidance will be on the prosthetic teeth.

Types of resin.

     a.Polymethylmethacrylatc. (PMMA) (Most commonly used.)

     b.Grafted polymethylmethacrylate.

     c. 4-meta (4-methacryloxyethyl trimellitate anhydride) containing PMMA.

                  Potential to chemically bond to alloys capable of oxidation so it
        reduce microleakage at metal-resin interface.

     d. Polyvinyl.

     e. Composite resin.

III- Combined Metallic and Acrylic Resin Bases:

        Acrylic resin bases attached to metallic denture framework through
metallic minor connectors.

       Metal resin interface exhibits a potential space which may enlarge during
thermo cycling and permit the entrance of microorganisms and fluids. This may
lead to discoloration, plaque accumulation and resin deterioration at the interface.

They are used in the following conditions:


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                                                                          Denture Base


   1. Free-end saddle cases as in Kennedy class I, II and IV and in class III cases
      having long edentulous spans to facilitate future relining. Relining is required
      to compensate for bone resorption and loss of support, which frequently
      occur in these cases.

   2. Patients vulnerable to an increased rate of bone loss as diabetic patients or
      patients on steroid therapy.

   3. Cases with extreme bone loss. The presence of acrylic resin is necessary to
      restore the original contour of the ridge giving more satisfactory results than
      metal bases.

   4. Long span cases.

   5. Recent extraction cases which will need early relining.

   6. Cases with bone resorption prognosis as diabetic patients.

   7. Class IV for appearance.



 Methods of Attaching Denture Bases

Denture Base Retention (Grid-work) minor Connector

             Acrylic resin bases are attached to metallic denture framework by
      means of a   minor connector designed so that a space exists between it
      and the underlying tissues of the residual ridge. (Relief of at least a 20-gauge
      thickness over the basal seat areas of the master cast is used to create a raised
      platform on the investment cast on which the pattern for the retentive frame
      is formed)

The minor connectors are either made in the form of

  a) Lattice work construction.

  b) Mesh construction.

  c) Bead, wire, or nail-head minor connectors (used with a metal base).


                                                                       Mostafa Fayad 13
                                                                                Denture Base


       Retentive mesh and retentive lattice are used when a plastic denture base will
contact the edentulous ridge.

      Loops, beads, and posts are used with a metal base to which prosthetic teeth
are attached with processed plastic.

This type of minor connector must be

     strong enough to anchor the denture base securely;

     rigid enough to resist breakage or flexing,

     Must not interfere as possible with arrangement of the artificial teeth.

Extension:

        In the maxillary arch if the denture base is a distal extension base (no
           tooth posterior to the edentulous space), the minor connector must extend
           the entire length of the residual ridge to cover the tuberosities.

        When a distal extension ridge in the mandibular arch is being treated, the
           minor connector should extend two-thirds the length of the edentulous
           ridge.




1- An open latticework (ladder-like pattern).

       The latticework consists of two struts of metal, pieces of
12- or 14-gauge half-round wax and 18-gauge round wax are
used to form a ladder like framework., extending longitudinally
along the edentulous ridge.

       A longitudinal strut should not be positioned along the ridge crest as it may
act as a wedge in the resin and may cause resin fracture.

       In the mandibular arch one strut should be positioned buccal to the crest of
the ridge and the other lingual to the ridge crest.


                                                                         Mostafa Fayad 14
                                                                              Denture Base


       In the maxillary arch one strut is positioned buccal to the ridge crest, and the
border of the major connector acts as the second strut.

       Smaller struts, usually 16 gauge thick, connect the two struts and form the
latticework. These connecting struts run over the crest of the ridge and should be
positioned to interfere as little as possible with arrangement of the artificial teeth.
Generally, one cross strut between each of the teeth to be replaced should be
satisfactory.

       The latticework minor connector can be used whenever multiple teeth are to
be replaced. It provides the strongest attachment of the acrylic resin denture base to
the removable partial denture. It is also the easiest of the denture base retainers to
reline if this becomes necessary because of ridge resorption.

       In construction, wax forms of the struts are positioned on the refractory
(investment) cast, which is duplicated from the master cast.



   It is necessary to provide a relief space over the dentulous ridges for both the
    latticework and the mesh minor connector so that there will be a space between
    the struts or mesh and the underlying ridge.

   It is in this space and around the struts or mesh that the acrylic resin denture
    base will be formed. The locking of the acrylic resin around and through the
    latticework provides the retention of the denture base.

   Relief under the grid-work should not be started immediately adjacent to the
    abutment tooth but should begin 1.5 - 2 mm from the abutment tooth.

   The junction of grid works to the major connector should be in the form of a
    butt joint with a slight undercut in the metal.

   The grid work on a mandibular distal extension should extend about 2/3 of the
    way from abutment tooth to retromolar pad but not on the ascending portion of
    the ridge mesial to the pad. It should has a “tissue stop” at their posterior limit
    to provide direct contact with the ridge.



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                                                                          Denture Base


   Maxillary distal extension grid-works should extend at
    least 2/3 of the length of the ridge to the hamular
    notch. However, the junction or finishing line of the
    maxillary major connector should extend fully to point
    to the hamular notch area so that the acrylic resin base
    can be extended into this area and provide a smooth
    transition from the connector to the base.




2- in a closed meshwork configuration (plastic mesh pattern).

     The mesh type of minor connector consists of a thin
      sheet of metal with multiple small holes that extends
      over the crest of the residual ridge to the same buccal,
      lingual, and posterior limits as does the latticework
      minor connector.

       It can be used whenever multiple teeth are to be replaced.

     The mesh pattern is less satisfactory as the space available for incorporating
      acrylic resin between metallic strips is narrow so it makes it more difficult to
      pack the acrylic resin dough because more pressure is needed against the
      resin to force it through the small holes and not allow for enough bulk of
      resin which become weak and may detached from the metal base. It also
      does not provide as strong an attachment for the denture base.



     The major difference between retentive mesh and retentive lattice is the size
      of the openings. Retentive mesh has small openings while retentive lattice
      has much larger openings.

     The mesh type tends to be flatter, with more potential rigidity, but may
      provide less retention for the acrylic if the openings are insufficiently large.

     The lattice type has superior retentive potential, but can interfere with the
      setting of teeth, if the struts are made too thick or poorly positioned.



                                                                      Mostafa Fayad 16
                                                                          Denture Base


    Both types are acceptable if correctly designed.




3- Metal denture bases

 Posts, loops, beads , nail head, wire loop retention or metal stop may be used to
 for retention of the resin. with metal denture base, which is cast so that it fits
 directly against the edentulous ridge; no relief is provided beneath the minor
 connector.




       The retention is gained by the projection of metal on this surface. These
projections may be

    beads (made by placing beads of acrylic resin polymer in the waxed denture
     base and investing, burning out, and casting these beads);

    wires that project from the metal base,

    In the form of nail-head.

   This form of denture base is hygienic because of better soft tissue response to
metal than acrylic resin. But it can not be relined adequately in the event that ridge
resorption takes place.

       This type should be used on tooth-supported, well-healed ridges and when
inter arch space is limited and the available vertical space is so limited that an




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                                                                         Denture Base


acrylic resin base would be thin and weak. Because relining is not possible metal
bases are generally not indicated for extension RPDs.

       Minor connectors forming mandibular distal extension bases extend
posteriorly about two-thirds the length of the edentulous ridge. They should be
slightly extended onto the buccal and lingual surfaces of the ridge. This design adds
strength to the acrylic denture base and helps to minimize-distortion of cured resin
bases, which occurs due to the release of strains after processing. However, minor
connectors for maxillary distal extension bases may sometimes be extended to
cover the entire length of the residual ridge.




Minor connectors forming denture bases should include tissue stops and
finishing line:

Tissue stops:(tissue foot)

   It is a foot included in the fitting surface of minor connector designed for
      retaining acrylic base.

   Tissue stops are integral parts of minor connectors.

   They provide stability to the framework during the stages of transfer and
      processing. They are particularly useful in preventing distortion of the
      framework during acrylic resin processing procedures.

   Altered cast impression procedures often necessitate that tissue stops be
      augmented subsequent to the development of the altered cast. This can be
      readily accomplished with the addition of autopolymerizing acrylic resin.

   Tissue stops are essential parts in the fitting surface of minor connectors.
      They are usually two or three in number that contact the cast.

   Tissue stops stabilize the framework on the master cast during processing
      as acrylic resin is packed in the retention spaces.



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                                                                                 Denture Base


    Tissue stops elevate the minor connectors, forming the denture base, from the
       ridge, by a space equal to the thickness of acrylic bases.

    They are formed by making holes 2×2 mm in the relief wax placed over the
       ridge during preparation of the master cast before duplication.




                                 a                     b

Tissue stops prevent settling of the framework downwards, and elevate the minor connectors by a
space equal to the thickness of acrylic base.

   Finishing index tissue stop:

    It is located distal to the terminal abutment and is
       a continuation of the minor connector contacting the
       guiding plane. Its purpose is to facilitate finishing
       of the denture base resin at the region of the
       terminal abutment after processing.



Finishing Lines:

        Finishing lines are butt joints created at the junction of major connectors
with the denture bases.

        Finish lines must be provided on all partial denture frameworks wherever
denture base resin and the metal join.

        A finish line allows the resin to terminate in a butt joint to produce a
smooth surface.

        In distal extension bases, these butt joint finishing lines, are made on both
the external and internal surfaces of the major connector where acrylic resin is



                                                                             Mostafa Fayad 19
                                                                             Denture Base


processed, while in short bounded metallic bases, the butt joint is required only on
the external surface where acrylic resin is packed, for the attachment of teeth.

External finish lines-:

       An external finish line is located on the polished surface of a partial denture
and is formed in the wax pattern.

       a.          External finish lines are formed during the formation of the wax
pattern by carving a sharp definite angle in the wax pattern at the junction between
the major connector and the minor connectors forming the denture base.

       b.      This angle should be less than 90 degrees to lock the acrylic resin
securely to the minor connectors and for the acrylic base to blend smoothly and
evenly with the major connector.

       c.      External finish line is positioned just far enough lingual to the ridge
crest to position the artificial teeth.

       d.      External finish line fades into minor connectors or proximal plates as
it approaches the occlusal surfaces of the contacting teeth.

       e.      The external finish line should never be placed directly over the
internal finish line. It should be placed superiorly to the internal finish line so that a
minimum amount of denture base resin is used on the lingual aspect of the teeth.




       For maxillary RPDs. the palatal finish line should be located so that it allows
for proper positioning of the artificial teeth while still maintaining normal tissue
contours and a smooth transition from metal to plastic. It should be located 2 mm
medial from an imaginary line that would contacts lingual surfaces of missing
posterior teeth.

       For a mandibular distal extension RPD, the external finish line begins at the
distolingual aspect of the terminal tooth and angles posteriorly as it progresses



                                                                         Mostafa Fayad 20
                                                                           Denture Base


toward the floor of the mouth. The lingual finish line for a mandibular tooth-
supported RPD should be located just far enough lingually to allow for setting of
the artificial teeth. If it is placed too far lingually (and thus inferiorly), the major
connector will be weakened.

Internal finish lines:

       An internal finish line is located on the internal or tissue surface and is
formed while blocking out the master cast.

        If the resin ends in a thin edge, saliva and debris will accumulate between
the denture base resin and the metal. The resin will also fracture if left too thin in
this area.

       a. Internal finish lines are formed by carving the relief wax used to create
space for packing acrylic resin under mesh minor connector. This relief wax is
applied on the master cast before duplication.

       b. In tooth-mucosa borne RPD the internal finishing line (IFL), it is placed
approximately at the junction of the vertical and horizontal planes of the palate to
permit proper relining since resorption of bone occurs all the way up to this level.
While in case of maxillary tooth borne PD, the IFL is slightly palatal to the EFL.

       c.    The internal finish line is located on the tissue surface side of the
framework. It is formed by the 24- to 26-gauge relief wax placed on the master cast
prior to duplication.

       d.    The internal finish line is normally placed farther from the abutment
tooth or residual ridge than the external finish line.

       e.     Internal finish line should be located to allow resin to cover mueo-
osseous areas where resorptive changes are anticipated. This permits the base to be
relined to reestablish mueo-osseous support.




                                                                        Mostafa Fayad 21
                                                                             Denture Base


       f.     Internal finish line should be located 3-4 mm from the natural teeth.
This allows a highly polished metal surface to be placed adjacent to the free
gingival margins.

       g.     Internal finish line should form a well defined butt joint with the
denture base resin.

       h.     Internal line angle of the internal and external finish lines should be
less than 90 degrees to provide mechanical retention for the denture base resin.

       i.     Internal and external finish lines should not be superimposed. A
staggered (offset) relationship maintains framework strength.

       j. The palatal extension of the internal finish line is determined primarily
by the need to reline the partial denture to compensate for anticipated bone
resorption.

                   For tooth borne partial dentures, the internal finish lines should be
                    placed slightly palatal to the external finish lines. This staggered
                    relationship contributes to increased framework strength and an
                    adequate thickness of resin between the finish lines. Placement of
                    the internal finish line more palatally is usually not indicated,
                    since only minimal resorptive changes occur.

                   For tooth-mucosa borne partial dentures, the internal finish lines
                    in the edentulous regions should be placed close to where the
                    vertical and horizontal planes of the palate meet. This position is
                    approximately 10 mm lingual to the previous position of the
                    lingual gingival margins of the missing teeth. This permits proper
                    relining, since bone resorption may occur up to this level. The
                    horizontal portion of the hard palate is relatively resis¬tant to
                    pressure-induced resorptive changes.




                                                                         Mostafa Fayad 22
                                                                                        Denture Base




              1                                      2                              3

 1: black arrow indicates the external finishing line(EFL) in tooth-mucosa borne RPD.
 2:. a case of maxillary tooth-mucosa borne RPD. arrow (A) indicates The internal finishing
 line(IFL), it is placed approximately at the junction of the vertical and horizontal planes of
 the     palate    to     permit     relining.     Arrow      (B)      indicates    the      EFL
 3: in case of maxillary tooth borne PD, the IFL is slightly palatal to the EFL




                                                  External finish lines: junction of major
                                                  connector and minor connectors at palatal
                                                  finishing line should be located 2 mm
                                                  medial from an imaginary line that would
                                                  contacts   lingual   surfaces    of     missing
                                                  posterior teeth.




Denture base extension

        Maximum coverage of the edentulous ridge is always desirable to allow
greatest area of bone to share in resisting the occlusal stresses exerted during
mastication. This helps in decreasing the force per unit area and keeping the forces
within the physiologic tissue tolerance.

a)      Antero-posterior extension

       - In bounded spaces: It is determined by the abutment teeth.

       - In free-end spaces: The base extends to cover the retromolar pad in the
       lower arch and hamular notches and tuberosity in the upper`.

b)     Buccally: The flange should extend to the mucosal reflection. The labial
flange is sometimes omitted for esthetic reasons.

                                                                                   Mostafa Fayad 23
                                                                                Denture Base


     c)     Lingually: The flange of the lower denture base should extend to the full
     depth of the lingual sulcus as permitted by muscle function.

            Lingual surfaces usually are made concave except in the distal palatal area.
     Buccal surfaces are made convex at gingival margins, over root prominences, and at
     the border to fill the area recorded in the impression. Between the border and the
     gingival contours, the base can be made convex to aid in retention and to facilitate
     the return of the food bolus to the occlusal table during mastication. Such contours
     prevent food from being entrapped in the cheek and from working under the
     denture.

            Occasionally, the path of insertion can cause the denture flanges to impinge
     on the mucosa above undercut portions of the residual ridge, when the partial
     denture is being seated. In these instances, it is usually preferable to shorten the
     flange, rather than relieving the internal surface. If the internal surface is
     relieved significantly, a space will exist between the denture base and the tissues
     when the denture is fully seated. Food may become trapped in the space and work
     its way under the partial denture.

     Relationship of denture base to abutment

     The ideal relationship between the denture base carrying the artificial teeth and the
     adjacent abutment should either be:

1-     Close contact between the denture and the proximal surface of the abutment. In
     this condition relieving the gingival margin is necessary to avoid its traumatization.

2-     Open Contact between artificial teeth carried by the denture base and the
     abutment above the contact point allowing enough space between them to create a
     cleansable area.

     On the other hand improper contact between the denture and the abutment tooth
     leaving only a small space between the neck of the abutment tooth and the artificial
     tooth is undesirable. This small space is difficult to clean predisposing to caries,
     gingivitis and pocket formation.


                                                                            Mostafa Fayad 24
                                                                                  Denture Base




Ideal base/abutment tooth relationship

1-Close contact between the denture and the proximal surface of the abutment

2- Open Contact. Enough spaces are self-cleansing.

AESTHETICS OF RPD IN RELATION TO THE LABIAL FLANGE:

LONG ANTERIOR SADDLE

       The natural appearance presented by the labial and buccal flange of a long
saddle is dependent upon:

     The shaping of the gingival papillae,

     The shaping of the gingival margins,

     The overall contouring of the flange as a whole, and

     coloring and shading.

       In shaping the gingival papillae, the space between the teeth should be
filled. The resin representing the papilla may then be lightly polished to give a
surface, which is readily self-cleansing.

       The shape of the entire gingival margin is usually more sharply curved if the
neck of the tooth is not prominent, but is higher and straighter if the neck is
prominent. A more vigorous expression may be obtained by emphasizing the
convexity of the gingival margin. The whole area of the gingival margin should be
polished highly to avoid food debris accumulating round the necks of the teeth.




                                                                               Mostafa Fayad 25
                                                                         Denture Base


       In ageing, both the interdental papilla and the gingival margin require
modification. The papilla is positioned higher on the neck of the tooth, and the
gingival margin regresses up the root of the tooth and a pointed rather than a curved
form should be used, especially at the neck of a prominent tooth such as the canine.

       Contouring of the labial flange should be carried out to simulate the
development of bony prominences over the roots of teeth and Interdental
depressions. Stippling of the attached gingiva, as well as giving a pleasing natural
appearance, has been found to restrict lip movement in some cases. The lateral
margins of labial flanges must be reduced to wafer thinness and be extended over
the root eminences of the abutment teeth.

       The thin edge allows the colour of the flange to blend more naturally with
the mucosa. Coloring and shading of labial flanges must be considered to blend
harmoniously with the natural tissues of the patient. Many manufacturers supply
acrylic materials containing colored fibers, to which may be added additional stain
and shaded polymers.

SHORT ANTERIOR SADDLE

The general principles discussed in relation to long anterior saddles apply equally
to shorter ones:

The artificial papilla must be shaped to match the natural closest papilla.

The shape and contour of the gingival margin must be similar to that of the
natural teeth.

The junction between artificial and natural gum tissue as mixed together as
possible.

       The margins of the flanges must be reduced to water thinness, and whenever
possible, extended over the eminences of the abutment teeth. Such thin edges not
only blend inconspicuously with the natural tissues, but also allow their colour to




                                                                      Mostafa Fayad 26
                                                                           Denture Base


show through. It will be necessary to employ a path of insertion that will allow the
thin acrylic to pass over the eminence.

2. A gum-fit can be done by using a longer tooth than is really indicated which is
unsightly when the necks of the teeth are revealed by the patient. Usually it is better
to use a small flange if possible since this can be very thin and discreet and nearly
undetectable at normal distances. The use of a flange also increases the saddle area
which is desirable whenever possible. Fitting to the gum is recommended in some
cases where the first premolar has to be replaced and the canine is still standing.

       The ridge just posterior to the canine is often quite prominent and the tooth
angulations will be better if no flange is used. In addition, a flange in this area is
often noticeable when the patient smiles.




                                                                       Mostafa Fayad 27
                                                            RESTS AND REST SEATS




                           RESTS AND REST SEATS


Definitions
    Rests:

      Are rigid extensions of a partial denture, fitted into rest seats, which are
  prepared on either the occlusal, lingual surfaces or incisal edges of the teeth,
  providing support to the partial denture.

    Support:

      The quality of the prosthesis to resist displacement towards denture
  supporting structures.

    Rest seat:

      The prepared recess in a tooth or restoration created to receive occlusal,
  incisal, or lingual rest.

Types of Rests:
       A- EXTRACRONAL (EXTERNAL) REST: which used with an
extracronal clasp assembly-type direct retainer although it is primarily within the
contours of the abutment tooth.

        According to their shape and location on the tooth surface they may be
classified as:

       1- Occlusal rest.

                 (1) Proximal occlusal (conventional),

                 (2)Interproximal

                 (3) Transocclusal (embrasure).

                 (4) Extended

       2- Incisal rest.

       3- Lingual rest.

       4- Embrasure Hooks

       5- Rest Recess


                                                                   Mostafa Fayad - 1 -
                                                            RESTS AND REST SEATS


       B- INTRACRONAL (INTRENAL) RESTS fit into rest preparations
within the contours of an abutment tooth crown. It is used with many precision
and semiprecision attachments.

        PRECISION RESTS consists of two metal components manufactured to
fit together precisely. One component is a box type rest seat, keyway or matrix
which is incorporated into the crown of an abutment tooth. The other component
is a rigid metal extension (patrix) which fits the matrix precisely and is
incorporated into the RPD.

       A SEMIPRECISION REST is a box-type rest seat,
keyway or matrix which is fabricated in the dental laboratory by
incorporating a preformed plastic pattern into the wax pattern for
the crown of the abutment tooth, or by waxing the crown pattern
around a special mandrel in the dental surveyor thus forming the
contour of the rest preparation. After the crown is cast, the matrix
is machined (milled) with a bur held in a surveyor. The pattern
for the patrix of the semi precision rest is formed by a performed
plastic pattern or by waxing directly to the matrix (rest preparation) in a crown
or a cast of the crown. The patrix is cast as part of the RPD framework.



Rests may be classified into

A- according to relation to direct retainer

  1- Primary rest: it is a component of direct retainer

  2- Secondary rest: it is an additional rest used on other than abutment teeth for
gaining extra support or act as indirect retainer.

B- According to shape:

 1- Saucer shape.                2- Box shape

 3- Dove tailed                  4- Triangle

 5- V- shape.                     6- Saddle shape

 7- Boomerang shape               8- Circular (conservative).

C- According to the abutment tooth

  1- Posterior rests

  2- Anterior rests



                                                                   Mostafa Fayad - 2 -
                                                            RESTS AND REST SEATS


I- Occlusal Rest:
       A rigid extension of a removable partial denture located on the occlusal
surface of a posterior tooth, on a rest seat specially prepared to receive it.

 Requirements of the Occlusal Rest:
      1. The occlusal rest must fit the tooth accurately to minimize the food
         collection beneath it and preserve its location in relation to the tooth.

      2. The angle formed by the occlusal rest and the vertical minor connector
         should be less than 90 o so that the transmitted occlusal forces are
         directed toward the long axis of the tooth.

      3. It should have sufficient thickness of metal to withstand the loads
         without deformation or breakage.

      4. It must not raise the vertical dimension of occlusion.

      5. In bounded partial denture: occlusal rests are placed in the near zone
         of the occlusal surface of the two abutments bounding the edentulous
         span.

      6. In free end partial dentures: the occlusal rest is placed on the far
         zone of the occlusal surface of the abutment, in order to decrease the
         torque action on the abutment tooth.

Functions of the Occlusal Rest
1. Support: it transmits forces from the prosthetic teeth to the abutment teeth so
   the main function of occlusal rest is to provide support to the partial denture
   against vertical forces, this prevent settling of the denture towards the
   underlying tissues, which will:

  a- Prevent a spreading of the clasp arms, and maintains the components of the
  dentures in their planned positions.

  b- Prevents impingement of the gingival tissues adjacent to the abutment
  teeth.

   N.B. partial denture without occlusal rests is called “gum stripper”.

2. Assist in distributing the occlusal load among two teeth or more so that each
   can bear a proportionate share of the masticatory load in concert with the
   residual ridges.




                                                                   Mostafa Fayad - 3 -
                                                             RESTS AND REST SEATS


3. Help maintain the plane of occlusion in the region of the abutment teeth.The
  occlusal rest can be shaped to improve the existing occlusion by building out
  the occlusal surface of the tooth to allow contact with the opposing teeth.

4. It may act as indirect retention along with its minor connector if they are
   placed beyond the fulcrum.

5. Maintain the clasp in the correct position on the abutment tooth thus helping
to maintain the effectiveness of the retentive and reciprocal components of the
clasp.
4. Serve as a reference point for evaluating the fit of the framework to the teeth.
5. Help prevent extrusion, tipping, or migration of the abutment teeth.
8. In addition to these functions, an internal rest may provide some bracing and
retention for the RPD.
Effect of occlusal rest location on the tooth :
         - An extended occlusal rest covering the whole occlusal surface of the
tooth "Onlay rest" allows for the transmission of the vertical load over the whole
occlusal surface and directs the forces along the long axis of the tooth.
         - An improperly extended occlusal rest placed on one side of the
occlusal surface causes torque on the tooth when vertical forces are applied. - To
prevent this torque either:
a) Extend the occlusal rest across the mesio-distal center of the tooth,
b) Use two short oppositely placed occlusal rests one on the mesial and the other
on the distal surface of the tooth,
Forms and Requirements of Rest Seat Preparation:
   1- Preparations for the occlusal rest must precede making master cast and
      follow proximal preparation (guiding planes and elimination of
      undesirable undercuts).

   2- Rest seats are prepared in sound enamel, cast restoration or rarely
      amalgam alloy. The use of amalgam restoration as support for an occlusal
      rest is the least desirable because of its tendency to flow under pressure
      and also because of the comparative weakness of a marginal ridge made
      of this alloy. Occlusal rests can be prepared in an old amalgam
      restoration.

   3- When a metal restoration (inlay, onlay or crown) is planned for an
      abutment tooth, the rest seat must be carved in the wax pattern of the

                                                                    Mostafa Fayad - 4 -
                                                             RESTS AND REST SEATS


       restoration and refined in the cast metal before the restoration is seated in
       the mouth.

   4- The out line form of an occlusal rest seat should follow the outline form
      of the fossa present on the occlusal surface and should be rounded
      triangular in shape, the base of the triangle – located at the marginal
      ridge- is about one third to one half the mesiodistal width of the tooth,
      it is about 2.5 mm in width, and its rounded apex is directed towards the
      center of the tooth .

   5- it should be one half the buccolingual width of the tooth from cusp tip to
      cusp tip which correspond to one third of the whole buccolingual
      diameter of the tooth

   6- The marginal ridge is lowered approximately one to 1.5 mm to permit
      sufficient bulk of metal to provide strength and rigidity to the rest without
      interference with the opposing teeth.

   7- The rest seats may be prepared in either a box shaped or saucer shaped
      form:

           Saucer- Shaped Rest Seat: preparation have
            concave, spoon or saucer shaped form to prevent
            locking of the occlusal rest and transmission of
            lateral and tipping forces to the abutment. They are
            used in free end saddle cases and bounded cases having weak
            abutments.

           Boxed Shaped Occlusal Rest have vertical walls and flat floor,
            they are rarely used in bounded cases having strong abutments.

   8- The rest seat should have smooth gentle curves with no sharp walls,
      angles or ledges.

   9- It should be deep enough to have sufficient space for sufficient bulk of
      the rest to be rigid without interference with occlusion. A rest seat is
      prepared to make room for the occlusal rest. Space for the rest should not
      usually be created by grinding the upper palatal cusp as this is a
      supporting cusp contributing to the stability of the intercuspal position.

   10- A The floor of the seat should be

   a- Inclined apically as it approaches the center of the tooth to direct the force
towards the long axis of the tooth.



                                                                    Mostafa Fayad - 5 -
                                                              RESTS AND REST SEATS


   b- The angle formed by the seat & the vertical minor connector should be
also less than 90o for directing the load towards the long axis of the abutment
and prevent slipping of rest creating an orthodontic like force and to direct the
forces along the long axis of the tooth.

   c- For distal extension partial denture it should be saucer or spoon to prevent
transmission of lateral forces to the abutments. The rest may move slightly in
function, like a ball and socket to dissipate horizontal forces.

   d- For bounded cases having strong abutments it may have relatively box-
shape.

         When an existing occlusal rest preparation is inclined apically toward the
reduced marginal ridge and cannot be modified or deepened because of fear of
perforation of the enamel or restoration, then a secondary occlusal rest must be
employed to prevent slippage of the primary rest and orthodontic movement of
the abutment tooth.

         Preparation of occlusal rest seats
         Rest seat preparations should be made in sound enamel.

       The preparation of occlusal rest seats always must follow proximal
preparation, never precede it. Only after the alteration of proximal tooth
surfaces is completed may the location of the occlusal rest seat in relation to the
marginal ridge be determined.

       Occlusal rest seats in sound enamel may be prepared with burs and
polishing points that leave the enamel surface as smooth as the original enamel.

       Occlusal rest seats in crowns and inlays are generally made somewhat
larger and deeper than those in enamel. Those made in abutment crowns for
tooth-supported dentures may be made slightly deeper than those in abutments
that support a distal extension base; thus they approach the effectiveness of
boxlike internal rests.

       1- The larger round bur is used first to lower the marginal ridge and to
establish the outline form of the rest seat.

       2- A slightly smaller round bur is then used to deepen the floor of the
occlusal rest seat.


                                                                    Mostafa Fayad - 6 -
                                                                RESTS AND REST SEATS


       When a small enamel defect is encountered in the preparation of an
occlusal rest seat, it is usually best to ignore it until the rest preparation has been
completed. Then, with small burs, prepare the remaining defect to receive a
small restoration.

       3- A fluoride gel should be applied to abutment teeth following enamel
recontouring. If the master cast will be fabricated from an irreversible
hydrocolloid impression, application of the gel should be delayed until after
impressions are made. This is because some fluoride gels and irreversible
hydrocolloids may be incompatible.

       Existing restoration may be perforated in the process of preparing an ideal
occlusal rest seat. The rest seat may be widened to compensate for shallowness,
but the floor of the rest seat should still be slightly inclined apically from the
marginal ridge. When this is not possible, a secondary occlusal rest should be
used on the opposite side of the tooth to prevent slipping of the primary rest.

Special Considerations for Rest Seat Preparation
1- Boxed shaped occlusal rest

           The box shaped rest seat is preferably prepared in a
    cast gold restoration. If it is sufficiently deep it is also provide
    guide-surfaces to control the path of insertion of the
    denture.

          It can be employed only on a strong periodontally healthy abutment.
    The rest seat has a flat floor, sharp line angles and nearly vertical walls. The
    box shaped rest helps in preventing lateral movement of the denture; it
    provides some bracing and retention for the RPD.

           It can be used on few occasions in bounded cases as it applies more
    torque on the abutment tooth.

2- Dove tailed occlusal rest: it may prepared in short span bounded saddle

3- Extended occlusal rest

       It may extend to the center of the tooth or entirely across the occlusal
surface. The purpose of extending the rest to the center of the tooth or across the
entire occlusal surfaces is to:



                                                                       Mostafa Fayad - 7 -
                                                              RESTS AND REST SEATS


       1) Direct forces more parallel to the long axis of the root than if the rest is
just on the mesial or distal of the tooth,

        2) Provide increased stabilization (bracing) of the tooth and sometimes.

        3) Provide occlusal contacts with the opposing teeth.

       The occlusal rest preparation which extends mesiodistally through the
occlusal surface of a tooth is sometimes called a CONTINUOUS REST
PREPARATION.

       The function of extended occlusal rest:

     1. Gain support from both teeth.

     2. Restores occlusion.

     3. Prevent the posterior molar from elongation.

     4. Eliminates the need for maxillary prosthesis/

     Indication

               In Kennedy Class II , modification 1, and Kennedy Class III
       situations in which the most posterior abutment is a mesially tipped molar
       to minimize further tipping of the abutment and to ensure that the forces
       are directed down the long axis of the abutment.

4- Interproximal Occlusal Rest Seats

       The design of a direct retainer assembly may require that interproximal
occlusal rests be used. The rest seats are prepared as individual occlusal rest
seats, with the exception that the preparations must be extended farther lin-
gually than is ordinarily accomplished.

      They are used to avoid interproximal wedging by the framework.
Additionally, the joined rests will shunt food away from contact points.

       It is located in a fossa adjacent to another tooth. Its size,
shape and dimensions are similar to the proximal occlusal rest
preparation EXCEPT that the flare of the facial margin is
limited by the proximal contact with the adjacent tooth. The
embrasure occlusal rest preparation rarely extends beyond the primary fossa.

In preparing such rest seats



                                                                     Mostafa Fayad - 8 -
                                                            RESTS AND REST SEATS


        1.   Avoid weakening or eliminating contact points of abutment teeth.

        2.   Sufficient tooth structure must be removed to allow for adequate
                     bulk of the component for strength.

        3.   Occlusion should not be altered.

        4.   Rest seat preparations are extended lingually to provide strength
               (through bulk) without overly filling interproximal space with
               minor connector. This type of preparation is rather difficult, and
               care must be exercised to avoid violation of contact points. The
               marginal ridge of each abutment should be sufficiently lowered
               (1.5 mm).

5- Transocclusal rests (Embrasure rest):

       A transocclusal rest preparation is similar in size and
shape to an embrasure occlusal rest preparation EXCEPT
that the preparation is extended facially to create space for
the rest and clasp arm to extend onto the facial surface of the
tooth

       The embrasure type of clasp is, basically, two simple circle clasps jointed
together, and the rest recesses should be fashioned on the two abutment teeth.

       This rest can be used to bridge a gap between teeth, thus providing an
effective roof over the vulnerable interdental area. It also prevents food
impaction between the spaced teeth.

       As a general rule, if an embrasure or interproximal occlusal rests are to be
used, the occlusal fossa of the adjacent tooth is also prepared with an embrasure
occlusal rest preparation UNLESS THERE IS A REASON NOT TO such as
occlusion, existing restorative material, etc.

6- Internal Rest (the milled rest, the semi precision attachment)

       The internal rest consists of narrow slot or key way, built into a metal
casting that has been constructed for an abutment tooth, and into which is fitted a
male attachment that has been made an integral part of removable partial denture
framework.

        An intracoronal rest is not a retainer and should not be confused with an
attachment . The form of the rest should be parallel to the path of placement,
slightly tapered occlusally, and slightly dovetailed to prevent dislodgment
proximally.

       Advantages:

                                                                   Mostafa Fayad - 9 -
                                                                RESTS AND REST SEATS


            1- It facilitates the elimination of a visible clasp arm
             buccally

            2- Permits the location of the rest seat in a more
             favorable position in relation to the tipping axis
             (horizontal) of the abutment.

            3- Provide both occlusal support and horizontal stabilization

        Indication: in partial denture that is totally tooth supported by means of
cast retainers on all abutment teeth.



7- Onlays:

      They are extended occlusal rests covering the whole occlusal surface and
extending buccally and lingually. They are retained by mechanical or adhesive
means. Onlays may be cast in gold or chrome cobalt.

Functions or Onlays:

      1. Provide partial denture support.

      2. Help in improvement of occlusion by increasing the reduced vertical
         dimension. (Correction of close bite).

      3. It could be constructed with reduced cusp angle to minimize the lateral
         component of force, which is destructive to the abutment teeth.

      4. Splinting: onlays can be constructed on multiple abutments and joined
         together during casting to help in splinting periodontally weak teeth.




            A Correctly-shaped onlay                 B: lncorrectly-shaped onlay




8- Rotated tooth:      the preferred treatment is either to:

 1-       Cover the crown with a restoration that realigns the surfaces of the
       tooth with the other teeth in the arch.




                                                                      Mostafa Fayad - 10 -
                                                            RESTS AND REST SEATS


 2-      Alter its axial surfaces sufficiently to render it more suitable for
      clasping and to place the occlusal rest in the mesial or distal fossa of the
      buccal or lingual side of the alveolar ridge.

 3-     If it is not practical to place the rest in either fossa, it should be
      remembered that the occlusal rest might be placed anywhere on the
      surface of the tooth where a properly designed recess can be prepared to
      support it.



9- Tipped molar (Mesially inclined mandibular molar):

       The severely tipped mandibular molar sometimes presents a problem for
the placement of an occlusal rest because it is so difficult to engineer the recess
in such a manner that stresses are directed along the long axis of the tooth.
Failure to direct the stress axially may permit the forces of occlusion to tilt the
tooth farther mesially.

       The recess for a typical mesially inclined mandibular molar should be
prepared with the floor perpendicular to the long axis of the tooth to avoid
tipping the tooth farther mesially.

The rest should be designed to prevent further tipping, it must direct forces
down the long axis of the tooth by either of one of these ways: -

  A) An additional occlusal rest in the distal fossa: A rest positioned in this
   way tends to counteract any tendency of the tooth to tip farther mesially.

  B) A rest preparation that extended from the mesial marginal ridge to the
   distal triangular fossa to minimize further tipping.

  C) When a casting is required, such as full veneer crown or onlay, it should
   be constructed with flat occlusal surface perpendicular to the long axis. A
   one to two millimeters bevel on the buccal and lingual surfaces and a two to
   three millimeter guide plane on the mesial surface will provide bilateral
   bracing and prevent further tipping of the tooth. The occlusion is restored
   with a chrome cobalt or gold occlusal overlay as part of partial denture.
   Such type of rest construction takes advantages of the inclined plane effect
   directing forces along the long axis of the tooth.




                                                                  Mostafa Fayad - 11 -
                                                              RESTS AND REST SEATS


II-Lingual Rests:
      A- Cingulum Rest (inverted V Rest).

      B. Ball Rest.

      C. Canine Ledge.

A- Cingulum Rest (inverted V Rest):

            The cingulum rest is a portion of a partial denture that is placed in
              an enamel seat at the cingulum or just incisal to it. This is confined
              to maxillary canines that have a gradual lingual incline and
              prominent cingulum. It is rarely satisfactory on mandibular
              anterior teeth due to inadequate thickness of enamel (Fig،3-94).

            The most satisfactory preparation is that placed on a prepared seat
              in a cast restoration (cast veneer crown, a three-quarter crown or
              an inlay) (Fig،3-95,3-96).

            When preparing a cingulum rest in a cast restoration, the rest seat
              should be planned and done on the wax pattern before casting the
              restoration.




                                          2 mm

                               1:1.5 mm               2.5:3




                                      Cingulum Rest



      Specification of Cingulum Rest Seat:

       1. A rounded inverted V-shaped preparation (half -moon shaped), on
the lingual surface of anterior teeth, having 2.5: 3 mm mesiodistal length, 2 mm.
Labiolingual width and 1.5 mm. in depth.

      2.      All sharp angles and undercuts should be eliminated.

      5.     The rest seat is broadest at the center and as it approaches the
proximal surfaces it merges with the normal anatomy of the tooth.



                                                                   Mostafa Fayad - 12 -
                                                            RESTS AND REST SEATS


       6. Properly designed cingulm rest on the canine, prevents movement of
the rest in a gingival direction and maintains tooth position.

B. Ball Rest

           Cingulum ball rests with rounded outline are placed on the mesial or
            distal halves on the lingual surfaces of all anterior teeth, usually at
            the junction of the gingival and middle one thirds. Having 1.5 mm
            depth and 2.5 mm width.

           Ball rest permits rotational movements to occur during function of
            tooth-mucosa born RPDs.

           Such rest may be prepared on tooth surfaces with sufficient enamel
            thickness or may be prepared in restorations placed in teeth with
            inadequate enamel thickness (Amalgam or pin ledge, cast
            restoration, etc.).

       Ball burnisher placed in rest seat preparation to verify
contour. When an axially directed force is applied on the ball
burnisher it should not slip out of the rest seat.



       C. Canine Ledge

       * It is a step-like preparation placed on the mesial or distal halves of the
lingual surfaces of the maxillary canine. Usually at the junction of the gingival
and middle one thirds. Having 1.5 mm depth.

      * The ledge rest seat should be perpendicular to the long axis of the tooth.
All undercuts and sharp line angles should be avoided.

       They are generally used where the tooth does not have a prominent
cingulum or where a finger-type rest is to be used .




        D. Lingual dimple-shaped rest preparation : it is employed when there
is limited surface on anterior teeth due to occlusal contacts.




                                                                  Mostafa Fayad - 13 -
                                                             RESTS AND REST SEATS




       E. individually cast chromium-cobalt alloy rest seat forms (attached to
lingual surfaces of anterior teeth by use of composite resin cements with acid-
etched tooth preparation), laminates, and composite resins have been
successfully used as conservative approaches to forming rest seats on teeth with
unacceptable lingual contours.

       F. Sapphire ceramic orthodontic brackets have also been bonded to the
lingual surfaces of mandibular canines and shaped as rest seats. These have
advantages over the metal acid-etched retained rest in that a laboratory step is
avoided and increased bond strengths are achieved.

       The major disadvantage to using orthodontic brackets is that removal of
the rest seat would necessitate that they be ground off with the potential of heat
generation and possible pulpal damage.

       Preparation of an anterior tooth to receive a lingual rest

       Preparation may be started by using an inverted, cone-shaped diamond
stone and progressing to smaller, tapered stones with round ends to complete the
preparation. All line angles must be eliminated, and the rest seat must be
prepared within the enamel and must be highly polished.

       Shaped, abrasive rubber polishing points, followed by flour of pumice,
produce an adequately smooth and polished rest seat. The floor of the rest seat
should be toward the cingulum rather than the axial wall. Care must be taken not
to create an enamel undercut, which interferes with placement of the denture

III- Incisal rest:
       It is a rigid extension of a removable partial denture that are placed at the
incisal angles of anterior teeth on prepared rest seats. They are used
predominantly as auxiliary rests or as indirect retainers.

       It is more applicable on mandibular teeth due to lack of adequate
thickness of enamel on the lingual surface.




                                                                   Mostafa Fayad - 14 -
                                                                      RESTS AND REST SEATS


        The rest seat is a saddle- shaped preparation in the form of a small, V-
shaped round notch located approximately 1.5 to 2.0 mm from the proximal -
incisal angle of the tooth. It is having about 2.5 mm wide and 1.5 mm deep.

        An incisal rest is more likely to lead to some orthodontic movement of
the tooth because of unfavorable leverage factors than is a lingual rest. The notch
should extend slightly onto the facial surface to prevent the tooth from moving
labially.

        An incisal rest seat is prepared in the form of a rounded notch at the
incisal angle of a canine or on the incisal edge of an incisor, with the deepest
portion of the preparation apical to the incisal edge. The notch should be
beveled both labially and lingually, and the lingual enamel should be partly
shaped to accommodate the rigid minor connector connecting the rest to the
framework. All borders of rest seat are rounded to avoid sharp line angles.
Proximal edge of rest seat is rounded rather than straight.

       N.B.: Whereas the most preferred site for a rest, is the occlusal surface of
a molar and premolar. If anterior tooth is the only abutment available, a canine is
preferred over an incisor. In the absence of canine multiple lingual rests are
prepared on anterior teeth.

                                                  2.0


                                                           1.5




          A- Lingual view demonstrates inclination of floor of rest seat, which allows forces to
be directed along the long axis of tooth as nearly as possible.

        The Lingual Rest is Preferable to an Incisal Rest because:

                     It is placed closer to the center of rotation of the abutment
                        tooth, thus it will exert less leverage and reducing its
                        tendency to tipping.

                     More esthetic, as it can be discreetly hidden from view.

                     It tends to be less bothersome to a curious tongue.

                                                                            Mostafa Fayad - 15 -
                                                            RESTS AND REST SEATS


Use of Incisal rest may be justified by the following factors:
      1. They may take advantage of natural incisal faceting.
      2. Tooth morphology does not permit other designs.
      3. Such rests can restore defective or abraded tooth anatomy.
      4. Incisal rests provide stabilization.
      5. Full incisal rests may restore or provide anterior guidance.



IV- Embrasure Hooks:
       Rests placed in embrasures between natural teeth extending slightly over
the buccal or labial surface but never extend below the survey line.

       They provide support, splinting of natural teeth, resistance to lateral and
anteroposterior movement and may act as indirect retainer.

      Their disadvantages are poor esthetics and wedging action on teeth.

      Functions:

      1- Resistance to anteroposterior movements.

      2- Help in splinting of the periodontally effected teeth.

      3- Support the denture

      4- Brace the denture

      Disadvantages of embrasure hooks:

      1- Bad esthetic.

      2- May cause separation of teeth by wedging action.




      V- Rest Recess
      In mandibular bicuspid with a rudimentary (undeveloped) cusp or in the
abraded tooth

                                                                  Mostafa Fayad - 16 -
                                                            RESTS AND REST SEATS


       The most satisfactory solution is to cover such a crown with a cast
restoration, building a cingulum rest into the wax pattern similar to the type used
for the canine tooth.

       VI-Quasicingulum rest
       It is prepared for lower first premolar having rudimentary lingual cusp
and consists of accentuated cingulum rest seat prepared in wax up of retainer.



DESIRABLE MATERIALS FOR REST PREPARATIONS

      Enamel and cast metal are ideal materials for rest preparations.
Porcelain is less desirable because of its propensity to fracture.

       Rest preparations may be prepared as an economic necessity in amalgam
but the flow and low yield strength of amalgam and the possibility of recurrent
caries and fracture of the tooth and/or restoration make amalgam an undesirable
material for a rest preparation.

       Dentin is an undesirable material for a rest preparation because of its low
abrasion resistance and propensity for caries. Unfortunately, dentin is frequently
exposed when placing rest preparations in natural teeth. In these situations the
tooth does not need to be restored unless it is sensitive or caries is anticipated.

       Conventional and resin composite are unacceptable materials for rest
preparations because of their low yield strength and low abrasion resistance.




                                                                  Mostafa Fayad - 17 -
                                                                    Major Connectors



                                CONNECTORS
       The various components of removable partial dentures are connected
together by connectors. Connectors are described as being either

       A-      Major connectors. B. Minor connectors

                          Major Connectors
       A major connector is the unit of R.P.D., which joins parts of the
prosthesis located on one side of the arch with those on the opposite side.

Functions of connectors:

  1. Join the component parts of the denture together.

  2. Contribute to the support of the prosthesis, by distribution of stresses
    applied to the prosthesis.

  3. They may contribute to the functions of bracing and reciprocation.

  4. Contribute to retention of the prosthesis

  5. Connectors resting on prepared dental or firm oral tissues provide indirect
    retention. Connectors that are relieved from the underlying tissues or lie on
    inclined surfaces do not provide indirect retention.

Classification:

a) According to the materials:       Metallic or non metallic .

b) According to the rigidity:        Rigid or non-rigid (stress breaking)

c) According to the dimensions:      Bar, strap or plate.

d) According to the location:        Maxillary or mandibular .

Principles for design for major connectors: see biomechanics

             L-bar or L-beam principle.

             Circular configuration.

             Strut configuration.




                                                                   Mostafa Fayad - 1 -
                                                                    Major Connectors

General requirements of major connector:

1-Rigid: Rigidity is necessary to transmit and distribute stresses over the entire
supporting area and from one side of the arch to the other.

Other components of the partial denture such as retentive clasps, occlusal rests,
and indirect retainers can be effective only if the major connector is rigid.

2- Must not impinge on the marginal gingiva:             It should provide vertical
support and protect the soft tissue to avoid impingement of the gingival margin.
In the maxillary arch the border of the     major connector should be located at
least 6 mm from the gingival margin, and 3mm in the mandible.

The border of the M C should be run parallel to the gingival margin of the teeth.
If the gingival margin must be crossed, the crossing should be at right angles to
the margin to produce the least possible contact with the soft tissues. Relief, or a
space, must be provided between the metal and soft tissue.

3- Must be properly located in relation to gingival and moving tissues. Bony or
soft tissue prominences should be avoided

4- Provide a means of obtaining indirect retention where indicated: The MC
may act as indirect retainer as in the form of lingual plate.

4- Provide an opportunity of positioning denture bases where needed; the
selection of the type of MC will at time be dictated by the location of the denture
bases replace the missing teeth. The location and number of denture bases
influence the type of MC that must be used.

5- Self cleansble not allow trapping of food particles

6- Not interfere with phonetics by using proper thickness and avoid covering the
rugae area if possible.

8- All adjoining minor connectors should cross-gingival tissues abruptly, and
should join major connectors at nearly a right angle.

7- Maintain patient comfort: Should provide patient's comfort through:


                                                                   Mostafa Fayad - 2 -
                                                                   Major Connectors

- Tapering the edges toward the tissues

- Prevent sharp angles or corners to prevent annoying tongue

- Prevent crossing of bony prominences as tori.

- Never place the connector on convex tooth surface or incisal third of teeth.

- The border should not end on the crest of prominent rugae but in the valleys

   between these crests.

- They should be symmetric on both sides and cross the palate in straight line



                 MAXILLARY MAJOR CONNECTORS
       A maxillary major connector is the unit of R.P.D., which joins parts of the
prosthesis located on one side of the maxillary arch with those on the opposite
side. Intimate contact between the tissue side of the maxillary major connector
and the palatal tissues is necessary for accommodation of RPD to enhance its
support, retention, and bracing.

General form of maxillary major connectors

       Maxillary major connectors are either in the form of bars, straps or
plates. The bars and straps are usually made of metals; the plates could be
entirely made of metal or sometimes a combination of metal and non-metal.
However bars cover less amount of tissues than plates.

        The term bar is used whenever the anteroposterior width of the major-
connector is less than 8 mm. If the anteroposterior width of the major connector
is in the 8 to 12 mm. range the term strap is applied. When more than 12 mm is
covered the term palatal plate is used. If the entire palate is covered, the term
complete palatal plate is used.

1-Bars

  a. Bars are usually narrow, less than 8 mm in width (6-8 mm) and half oval
     in cross section. Their margins are beveled and gently curved.

  b. They cover lesser amounts of tissues.




                                                                  Mostafa Fayad - 3 -
                                                                         Major Connectors

  c. However, bars require more bulk of metal in order to gain the required
     rigidity; this bulk may interfere with proper speech and may be untolerated
     by patients.

2-Straps

  a. They are wide and thin palatal bars, more than 8 mm in width to gain the
     necessary rigidity.

  b. Having a uniform thickness, its width could be increased in distal
     extension base.

  c. The palatal strap is well tolerated because it is not bulky.

  d. A wide strap helps in the distribution of stresses of mastication over a
     wider area of the palate and thus provides adequate support.

3-Extended palatal plates:

  a. the words palatal plate are used to designate any thin, broad, contoured
     palatal coverage used as a maxillary major connector and covering one
     half or more of the hard palate.

  b. The maximum area coverage contribute to

        i.       Wide distribution of the stresses falling on denture.

       ii.       Better support and retention of the prosthesis.

      iii.       Better horizontal stabilization of the prosthesis

Structural Requirements of Maxillary Major Connectors
 1. PLACEMENT OF BORDERS

      a. The borders are placed at least 6 mm from the gingival margins.
      b. When a 6 mm distance from the gingival margins cannot be
             obtained, the metal may be extended onto the cingula of anterior
             teeth or onto the lingual surfaces of the posterior teeth.
      c. All borders should be tapered slightly towards the tissues to be
             less perceptible to the patient.
      d. The finished borders should be smoothly curved.
      e. In the rugae region the border should pass through the valleys
             between the crests of the rugae when possible.

                                                                     Mostafa Fayad - 4 -
                                                              Major Connectors

      f. The posterior border should not extend onto the movable soft
         palate,
      g. The borders should be beaded.
      h. Both anterior and posterior borders should cross the midline at
         right angles, never diagonally.
      i. The borders should run parallel rather than diagonal to the
         gingival margin and if they cross the gingival margin they should
         be crossed abruptly and at right angle to the margin in order to
         produce the least possible soft tissue coverage.
2. THE METAL SHOULD NOT BE HIGHLY POLISHED ON THE
TISSUE SURFACE: to preserve intimate tissue contact, except where it
crosses the gingival margin
3. RELIEF OF THE MAJOR CONNECTOR.
      Usually no relief is required on the tissue surface of the major
connector. When crossing the gingival margins, the tissue surface should
be lightly relieved and highly polished. Little relief may be required in the
presence of palatal tori or prominent median
4. THICKNESS OF THE METAL should be uniform throughout the palate.

5. FUTURE LOSS OF ATURAL TEETH. When future loss of natural
teeth is anticipated a plate type design may be used. The plate should
extend onto the cingula of anterior teeth or onto the lingual surfaces of
posterior teeth.

6. INTERNAL AND EXTERNAL FINISH LINE: see denture base

7. TISSUE STOPS: see denture base
8. BEADING
      Beading is a term used to denote the scribing of a shallow
groove on the maxillary master cast outlining the palatal major
connector exclusive of rugae areas

  1.     A palatal major connector should have a specially
    prepared seal along the border of the connector where it
    contacts the soft tissues.


                                                             Mostafa Fayad - 5 -
                                                                    Major Connectors

  2.      The seal is formed by a beading at the border of the major connector
    that displaces the soft tissues slightly, this preventing food from collecting
    under the maxillary major connector and help in preventing over growth of
    the palatal tissues.

  3.      Beading is readily accomplished by using an appropriate instrument,
    such as a cleoid carver. Care must be exercised to create a groove not in
    excess of 0. 5 mm in width or depth at the edge of the design of the
    maxillary major connector. The groove must fade out as it approaches within
    6mm of the marginal gingiva. It also should fade out over the center of the
    cast when a hard midline suture is present.

Advantages of beading:
1- Prevents food debris from collection under the MC.

2- Provide a thinnest metal on the polished surface while maintain the necessary
strength. This is due to the extra thickness of metal provided by the beading.

The purposes of beading are as follows:

1. To transfer the major connector design to the investment cast

2. To provide a visible finishing line for the casting

3. To ensure intimate tissue contact of the major connector with selected palatal
tissue

Six basic types of maxillary major connectors are considered: Mac

1. Single palatal bar

2. Anterior-posterior palatal bars connector

3. Single palatal strap

4. U-shaped palatal connector

5. Combination anterior and posterior palatal strap type

6. Palatal plate-type connector




                                                                   Mostafa Fayad - 6 -
                                                                    Major Connectors

 MAXILLARY MAJOR CONNECTORS

 I- PALATAL BARS
 Palatal bars may be in the form of single palatal bars or combined palatal bars.

 1- Anterior palatal bar
        Indication:

                 It is rarely used alone but might be included
         in the design in conjunction with posterior palatal
         bar when indirect retention is required as in Kennedy
         class I and II or long span class III.

        Design:

           It is located in the anterior palatal region, sometimes used when
            anterior teeth are missing.

           The bar should be located 6-8 mm behind the gingival margin of
            anterior teeth.

       Disadvantages

            a. The anterior palatal bar is intolerable by patients as it crosses the
               palatal rugae where tongue activity is marked.

            b. Speech difficulties may be encountered.

 2- Middle palatal bar

        Indication:

       The middle palatal bar is single bar, mainly used in short
 bounded edentulous spans.

        Design:

- The bar crosses the middle portion of the palate away from the
  rugae area.

       Advantages:

   a. It is comfortable, well tolerated and inconspicuous by the tongue, hence
      speech is not affected as the bar crosses the mid-palatal area away from
      both the rugae area and the tongue.

   b. It provides some support since it lies on the horizontal part of the palate.


                                                                   Mostafa Fayad - 7 -
                                                                   Major Connectors

  c. Bracing is achieved because the bar prevents lateral movement of the
     appliance.

      Disadvantage:

  a. It lacks the required rigidity unless made bulky.

  b. It cannot be used in cases having large torus palatinus or prominent
     median palatine raphe.

3-Posterior palatal bar
       Indication:

       The single posterior palatal bar has limited indications for use. It is used
in tooth supported posterior dentures and in unilateral distal extension partial
denture replacing one or two teeth.

       Design:

  a. It is located in close relation to the junction of the
     hard and soft palate, or placed in level with the
     second molar.

  b. The bar is narrow and half oval in cross-section.

      Advantages

  a. The bar exhibits limited palatal coverage and well tolerated by the tongue
     if made with proper thickness. It is not likely to affect taste.

  b. Bracing is provided by the part of the bar contacting the lateral side of the
     palate.

  c. The posterior palatal bar provides indirect retention for Kennedy class IV
     cases.

      Disadvantages:

  a. It is rarely used nowadays, because it cannot be made bulk, thus lacks the
     required rigidity.

  b. It cannot be used in cases having an extended large torus palatinus.




                                                                  Mostafa Fayad - 8 -
                                                                          Major Connectors

Single Posterior Palatal Bar:

      Indications: In tooth- borne partial denture when second premolars and or
   first molars are missing.

     Design:

1. It is a narrow half oval with its thickest point at the center.

2. It is gently curved and should not form a sharp angle at the junction with the
   denture base.

3. It should not be placed further anterior to the second premolar. This position
   is favorable for the tongue action.

    Disadvantages:

1. For a single bar to maintain any degree of rigidity it should be bulky (less
   acceptable by the patient).

2. It drives little support from the bony palate because its narrow anteroposterior
   width.

3. Its use is limited to replace one ore two teeth on each side of the arc.

4. It is used only in interim PD until the definitive treatment can be rendered.


                Anterior PB       Middle PB                          Posterior PB
Location        Nearly 6mm away Between the 1st molars               Its posterior border
                from the gingival                                    lies at the junction
                margin                                               between the hard and
                                                                     soft palate
Cross section   Flat                      Flat                       Half oval
Function        Connection          and   Connection                 Connection        and
                indirect retention in                                indirect retention in
                class I & II                                         class IV
Tolerance       Poor                      Well tolerated             Well tolerated
Stability       Gives lateral stability
Indications     When a torus prevent      Class III
                usage of middle or        Unilateral free end saddle
                posterior PB
Esthetics       Satisfactory              Satisfactory               Satisfactory




                                                                        Mostafa Fayad - 9 -
                                                                        Major Connectors

4- Anteroposterior palatal bar (Ring Design, A-P bar)

Indication

  1. It can be used in any class especially when the anterior and posterior
  abutments are widely separated.

  2. When a patient objects a large amount of palatal coverage.

  3. It is almost used in any design especially in the presence of torus palatinus
  and in dentures restoring anterior teeth.

Design:

      Anterior palatal bar

       - Flat thin, wide bar located 6 mm away from the
         gingival margin of anterior teeth. Its borders should
         be placed in the depressions and slopes of the rugae, never on their crests.

  Posterior palatal bar

      - Thick bar, half oval in cross-section, located as far
       posteriorly on the hard palate, preferably in level with the
       second molar.

      - Both anterior and posterior connectors should cross the
       midline at a right angle rather than diagonally.

  Longitudinal bars:

  -       Two bars, one on each side of the palate, at the junction of its horizontal
      and vertical planes. They join the anterior and posterior bars forming the
      ring or circle configuration. Thus, the metal forming the connector lies in
      two different directions giving the connector strength and rigidity.

Advantages:

  a. The A-P bar is the most rigid bar type palatal major connector because it
     lies at different planes.

  b. It attains minimal soft tissue coverage

Disadvantages:

            The anteroposterior bars should not be considered as the first choice
      because of the following disadvantages:

      1. Provides little support from the palate.

                                                                      Mostafa Fayad - 10 -
                                                                      Major Connectors

   2. The anterior bar covers the rugae area and may interfere with phonetics
   and patient's comfort.

   3. Because the bars are narrow, extra bulk is required for rigidity.

   4. The multiple borders and edges of the bars may annoy the tongue and are
   intolerable by some nervous patients.

Contraindications:

               a. The A-P bar is contraindicated in the following cases.

               b. Patients exhibiting high, narrow palatal vault.

               c. Patients having large tori extending to the junction of the hard
                  and soft palate.



II- PALATAL STRAPS
The palatal strap is a wider and thinner than palatal bar, having uniform
thickness.

1- anterior palatal strap (palatal horse-shoe, U-shaped)
Indications:

               a. When several anterior teeth are being
                  replaced. The palatal horse-shoe is primarily
                  indicated when posterior teeth are to be
                  replaced especially when a large torus exists.

               b. In tooth-borne partial dentures with anterior
                  and posterior teeth are missing.(bounded
                  saddle).

               c. When a hard midline suture or palatal torus
                  cannot be covered.

               d. Tooth-supported       unilateral       edentulous
                  situations with provision for cross-arch attachment by either
                  extracoronal retainers or internal attachments.

Characteristics and Location:

               a. It consists of U-shaped thin band of metal. The anterior
                  border placed 6 mm away from the gingival margin lying in
                  the valleys rather than the crests of the rugae area.

                                                                    Mostafa Fayad - 11 -
                                                                 Major Connectors

              b. Posterior border at right angle to median suture line.
              c. If the strap carried onto the cingula, the gingival margin must
                 be lightly relieved.

              d. The lateral borders lies at the junction of the horizontal and
                 vertical slopes of the palate.

              e. All borders should be curved, smooth and beaded.

              f. Strap should be 8 mm wide or approximately as wide as the
                 combined width of a maxillary premolar and first molar.

              g. Confined within an area bounded by the four principal rests.


   When increased rigidity is required, metal thickness in the central portion
    may be increased to 1.5 mm, or the width of the major connector may be
    increased to lie in two planes.
   A common error in the design of a U-shaped connector, is its proximity to or
    actual contact with gingival tissue.


Blockout and Relief of Master Cast

    (1) Usually none required except slight relief of elevated medial palatal
    raphe or any exostosis crossed by the connector.

    (2) One thickness of baseplate wax over basal seat areas (to elevate minor
    connectors for attaching acrylic resin denture bases).

Beading

Waxing Specifications

          Anatomic replica pattern equivalent to 22- to 24-gauge wax
    depending on arch width.

Finishing Lines

      (1) Undercut and slightly elevated.

      (2) No farther than 2 mm medial from an imaginary line contacting lingual
      surfaces of principal abutments and teeth to be replaced.

      (3) Follow curvature of arch.



                                                               Mostafa Fayad - 12 -
                                                                        Major Connectors

 Advantages:

                a. The connector provides some vertical support.

                b. Indirect retention may be provided.

                c. It solves the problem of missing anterior teeth especially when
                   there is deep anterior vertical overlap.

 Disadvantages:

                a. The palatal horse-shoe is a poor connector because it lacks the
                   necessary rigidity, this major connector should be avoided
                   whenever possible

                b. Lack of rigidity causes movement or spreading of the lateral
                   borders of the connector when vertical force is applied.

                c. To obtain enough rigidity it should be made bulky, but this
                   could interfere with phonetics and might cause discomfort.

                d. It covers the rugae area and interferes with phonetics and
                   patient's comfort.

 Contraindication:

                For reasons of torque and leverage, a single palatal strap major
                connector should not be used to connect anterior replacements with
                distal extension bases.



 2-Middle Palatal Strap: [some text consider posterior palatal = (midpalatal) strap.]
       The middle palatal strap is the most versatile and widely used
 maxillary major connector.

Indications:

      a. Tooth borne and tooth and tissue borne unilateral
      edentulous spaces for cross arch stabilization.

      b. May be used for most maxillary tooth borne
         partial dentures when posterior teeth are missing.

      c. May be used for tooth-mucosa borne partial dentures when minimal
         palatal support is required.



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                                                                     Major Connectors

Design:

      The strap lies on the central portion of the hard palate.

      It consists of a wide, thin band of metal that crosses the palate.

      Its anterior border should be posterior to the rugae area and the posterior
              border should terminate short of the junction of the hard and soft
              palate

      The anteroposterior dimension of the middle palatal strap is usually little
             greater than the posterior palatal strap.

Advantages of the middle palatal strap:

   1. Provide greatest rigidity with less bulk of metal, because it is located in
     three planes (horizontal, or vault of the palate; the vertical or lateral slopes
     of the palate; the sagittal, or anterior slope of the palate).

   2. Reduces gingival margin coverage to a minimum.

   3. It is well tolerated because it can be kept away from the sensitive area
     around the rugae and incisive papilla.

   4. The anterior border lies just posterior to the commencement of the rugae
     area, where the number of tactile receptors is smallest.

   5. It is rarely annoying to the patient.

   6. It can be made relatively narrow, for the small tooth supported prosthesis,
     or much wider when the edentulous spaces are longer and the requirement
     for support is correspondingly greater.

   7. There is also minimal interference with phonetics.

   8. It provides support to the partial denture since it covers a relatively
     large area of the palate.

Disadvantages:

     The patient may complaint from excessive palatal coverage.



3-Posterior Palatal Strap
       This is basically a wide palatal bar, because it is wider it may be made
thinner, it should be a minimum of 8 mm. in width, and 1.5mm thickness.

Indication:
                                                                   Mostafa Fayad - 14 -
                                                                      Major Connectors

       - In maxillary unilateral tooth borne RPDs of short span.

Advantages:

                      1. It provides better support than a palatal bar.

                      2. It distributes stresses of mastication over a wider area than
                         a palatal bar.

Disadvantages:

                      1. The increased coverage of the palate as compared to the
                         palatal bar may be objectionable to some patients.

                      2. There may be some alteration of taste if made very wide.

Structural details:

    1. The border should be beaded.

    2. Should be wide (a minimum of 8 mm width) and thin (1.5 mm
       thickness).

    3. Thicker central area for increased rigidity.



4- Anteroposterior palatal strap (Closed Horseshoe):
      The anteroposterior palatal strap is a rigid connector;
indication:

      (1) Class I and II arches in which excellent abutment
     and residual ridge support exists, and direct retention
     can be made adequate without the need for indirect
     retention.

     (2) Long edentulous spans in Class II, modification 1
     arches.

     (3) Class IV arches in which anterior teeth must be
     replaced with a removable partial denture.

     (4) Inoperable palatal tori that do not extend posteriorly to
     the junction of the hard and soft palates.

     (5) In tooth borne, and mucosa borne partial dentures when replacement of
     anterior and posterior teeth is required.



                                                                    Mostafa Fayad - 15 -
                                                                 Major Connectors

Characteristics and Location:

          The connector has similar location and structure to that of the
   anteroposterior palatal bar except that both the anterior and posterior
   components are in the form of straps.

     (1) Parallelogram shaped and open in center portion.

     (2) Relatively broad (8 to 10 mm) anterior and posterior palatal straps.

     (3) Lateral palatal straps (7 to 9 mm) narrow and parallel to curve of
        arch; minimum of 6 mm from gingival crevices of remaining teeth or
        should extend above the height of contour of the teeth..

     (4) Anterior palatal strap:

             anterior border positioned as back as possible on the rugae area to
       minimize interference with speech , not placed farther anteriorly than
       anterior rests and never closer than 6 mm to lingual gingival crevices;
       follows the valleys of the rugae at right angles to the median palatal
       suture.

            Posterior border, if in rugae area, follows valleys of rugae at right
       angles to the median palatal suture.

     (5) Posterior palatal connector: posterior border located at junction of
        hard and soft palates and at right angles to median palatal suture and
        extended to hamular notch area(s) on distal extension side(s).

     (6) Anatomic replica or matte surface.

 Blockout and Relief of Master Cast

     (1) Usually none required except slight relief of elevated median palatal
       raphe where anterior or posterior straps cross the palate.

     (2) One thickness of baseplate wax over basal seat areas (to elevate minor
        connectors for attaching acrylic resin denture bases).

 Waxing Specifications

     (1) Anatomic replica patterns or matte surface forms of 22-gauge
       thickness.

     (2) Posterior palatal component—A strap of 22-gauge thickness, 8 to 10
        mm wide (a half-oval form of approximately 6-gauge thickness and
        width) may also be used.


                                                               Mostafa Fayad - 16 -
                                                                    Major Connectors

 Finishing Lines

     Same as for single broad palatal major connector.

Advantages:

               a. Rigidity and strength of the connector because it lies at two
                  different planes, allow the metal to be used in thinner sections.

               b. Provides good support due to wide palatal coverage.

               c. Good retention and stability could be achieved.



III- Extended palatal plate (Complete Palatal Coverage)
       A palatal plate connector covers half or more of the palatal surface. It is
a uniformly shaped, thin plate reproducing the anatomic contour of the palate. It
is characterized by wide palatal coverage contributing to maximum support and
retention, also helps in horizontal stabilization and bracing of the restoration..

Types of complete palatal plates

    1- Metal plate: Complete cast metal plate covering more
           than half of the palate.


    2- Resin plate: Complete resin plate covering the whole
            palate. see denture base for detail

    3- Combination, metal, and resin plate: Anterior metallic
          part having provisions for mechanical retention to
          attach an acrylic posterior portion.

Indications:

  1. Class I partially edentulous arches when all posterior teeth are to be
     replaced. (Only six remaining anterior teeth).

  2. If anterior edentulous areas are present in conjunction with bilateral distal-
     extension bases.

  3. Class II arch with a large posterior modification space and some missing
      anterior teeth.
  4. Cases having shallow vault or flat ridge as the complete plate will provide
     good stabilization.

  5. Where heavy occlusion demands maximum support.
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                                                                   Major Connectors

  6. Class III Kennedy with modifications, when the condition of the abutment
     is poor.

  7. Patients with cleft palate.

  8. When the partial denture is considered a transitional prosthesis (acrylic
     palatal plate is used).

  9. Should be used whenever maximum tissue support is desired.

  10. V- or U-shaped palates

Characteristics and Location:

      The anterior border of the plate is either placed 6: 8
   mm away from the gingival margin following valleys of
   rugae as near right angle to median suture line, or the
   anterior border may be extended to lie on the survey
   line or above cingulae of anterior teeth, in this case-the
   gingival margin should be slightly relieved.

      The posterior border of the plate at right angle to the median suture line;
   extended to pterygomaxillary notches (hamular notch )area(s) on distal
   extension side. It extends to the junction of the hard and soft palate. It should
   provide a peripheral seal, which adds to the retention of the denture.

            The borders are beaded to prevent debris from collecting beneath the
   plate.

             The posterior palatal seal that is used with complete dentures
      can not be used with a removable partial denture. Because of the
      rebound of the tissues under compression, place unnecessary extra
      forces on the abutment teeth. The intimate contact of the cast metal
      palate aids retention through adhesive and cohesive forces.

             The palatal plate should be located anterior to the posterior palatal
      seal area. The maxillary complete denture's typical posterior palatal seal
      is not necessary with a maxillary partial denture's palatal plate because of
      the accuracy and stability of the cast metal.

Blockout and Relief of Master Cast

      (1) Usually none required except relief of elevated median palatal raphe
      or any small exostoses covered by the connector.

      (2) One thickness of baseplate wax over basal seat areas (to elevate minor
      connectors for attaching acrylic resin denture bases).

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                                                                     Major Connectors

Waxing Specifications

      Anatomic replica pattern equivalent to 24-gauge sheet wax thickness.

Finishing Lines

      (1) Provision for butt-type joint at pterygomaxillary notches.

      (2) Undercut and slightly elevated.

      (3) No farther than 2 mm medial from an imaginary line contacting the
      lingual surfaces of the missing natural teeth.

      (4) Following curvature of arch.

Advantages:

  1. The plate is well tolerated by most of the patients. Its uniform thinness and
     the thermal conductivity of the metal are designed to make the palatal
     plate more readily acceptable to the tongue and underlying tissue.

  2. The plate covering different palatal planes provide more rigidity.

  3. The extensive area coverage contributes to:

                 a- Wide distribution of load and maximum support of the
                 prosthesis.

                 b- Horizontal stabilization (reduce the movement of the base
                 during function).

                 c- Direct-indirect retention due to the extended extension that
                 increased interfacial surface tension, good peripheral seal and
                 physiologic retention by dorsum of the tongue.

  4. The plate may help in splinting periodontally weak teeth.

  5. It offers maximum rigidity, support and retention to the partial denture

Disadvantages:

   a- The plate cannot be used in the presence of palatine tori.

   b- Full coverage may cause tissue inflammation if adequate oral hygiene is
   not practiced and it may cause alteration in taste.

   c- Complete palatal coverage may alter taste and tactile sensation.




                                                                   Mostafa Fayad - 19 -
                                                                   Major Connectors




    The palatal plate may be used in any one of three ways.
    1- As a plate of varying width that covers the area between two or more
edentulous areas,
    2- As a complete or partial cast plate that extends posteriorly to the junction
of the hard and soft palates,
    3- or in the form of an anterior palatal connector with a provision for
extending an acrylic resin denture base posteriorly.

Modified palatal plate
Indications:

a. Tooth-Mucosa Borne RPDs.

b. When complete palatal coverage is either not required or
unacceptable to the patient.

The width varies proportionate1y with

 1- The requirement for muco-osseous support

 2- The length of the edentulous span

3- Amount   of anticipated occlusal forces

4- Bone index of abutment teeth or the residual ridge

5- Periodontal status of abutment teeth

Split maxillary major connectors
Permits a variable degree of independent movement of
the muco-osseous supported segment of the RPD.

Indications.

     a.May be used where some stress release from the
     abutment teeth is desired through the major
     connector.

     b.May be used in place of stress releasing clasps or stress
     directors.

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                                                                    Major Connectors

Design:

     a.Degree of stress release is determined by the width and
     thickness of the connection remaining and by the type of
     metal used.

     b.Separation of the segments should be wide enough or
     very narrow to avoid pinching the tongue or palatal
     mucosa.

     c.The cast framework can flex in a single plane without
     work hardening and eventual fracture.




Sequence of design considerations for a maxillary major
connector:
      In 1953 Blatterfein described a systematic approach to designing
maxillary major connectors. His method involves five basic steps and is
certainly applicable to most maxillary removable partial denture situations.

Step 1: Outline of primary bearing areas. The primary bearing areas are those
that will be covered by the denture base(s).

Step 2: Outline of nonbearing areas. The nonbearing areas
are the lingual gingival tissue within 5 to 6 mm of the
remaining teeth, hard areas of the medial palatal raphe
(including tori), and palatal tissue posterior to the vibrating
line. (Nonbearing areas outlined in black).

Step 3: Outline of connector areas. Steps 1 and 2, when
completed, provide an outline or designate areas that are
available to place components of major connectors.

Step 4: Selection of connector type.

    Selection of the type of connector(s) is based on four factors: mouth
comfort, rigidity, location of denture bases, and indirect retention.

      To achive mouth comfort connectors should be of (1) minimum bulk ,(2)
positioned so that interference with the tongue during speech and mastication is
not encountered.



                                                                  Mostafa Fayad - 21 -
                                                                Major Connectors

      Connectors should have a maximum of rigidity to distribute stress
bilaterally.The double-strap type of major connector provides the maximum
rigidity without bulk and total tissue coverage.

      In many instances the choice of a strap type of major connector is limited
by the location of the edentulous ridge areas. When edentulous areas are
located anteriorly, the use of only a posterior strap is not recommended. By the
same token, when only posterior edentulous areas are present, the use of only an
anterior strap is not recommended.

      The need for indirect retention influences the outline of the major
connector. Provision must be made in the major connector so that indirect
retainers may be attached.

Step 5: Unification. After selection of the type of major connector, the denture
base areas and connectors are joined.




                                                              Mostafa Fayad - 22 -
                                                                   Major Connectors

               B- MANDIBULAR MAJOR CONNECTORS
       Mandibular major connectors used in partial dentures are either in the
form of bars or plates. The bars are usually located on the lingual side of the
ridge between the gingival margin and the floor of the mouth, while the plates
may be extended above the gingival margin to end on the lingual surfaces of the
natural teeth.

Structural Requirements for Mandibular Major Connectors:

1- PLACEMENT OF BORDERS.

    a. The superior borders are placed a t least 3 mm from the gingival margins
    and parallel to the free gingival margin or for the lingual plate it should be
    extends to the cingulae of the anterior teeth in which the gingival margin
    should be relieved.

    Where a 3 mm distance from the gingival margins cannot be obtained, the
    metal should extend on to the cingula of anterior teeth or onto the lingual
    surfaces of the posterior teeth.

    b. The inferior border should be gently rounded above the moving tissues of
    the floor of the mouth and should not interfere with the soft tissue movement
    of the floor of the mouth.

2. Beading is never indicated because of the need for relief under all mandibular
major connectors,

3- The metal should be highly polished on the tissue side to minimize plaque
accumulation.

4-RELIEF: Relief (0.5-1mm) must be provided between the mandibular major
connectors and the soft tissue to prevent the margins of the connectors from
inflammation or laceration the friable lingual mucosa during movement.

       The amount of relief depends on

a) The type of removable partial denture.

       - For an all tooth-supported prosthesis a minimum of relief is needed

       because the denture does not tend to move, (30 gauge, 0.010 inch)

       - Where in a distal extension partial denture needs more relief because

       it tends to rotate during function.

b) The slope of the lingual tissue.

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                                                                                  Major Connectors

       If the lingual slope is near vertical, this needs minimal relief. If the lingual

       slope is toward tongue, maximum relief is needed. If lingual slope have

       undercut, sufficient space which may create during blocks out the

       undercut, and not need additional relief.




                A. Slope of tissue is nearly vertical; minimal relief is needed

                 B- Tissue slope toward the tongue, maximum relief is needed

                 C- Lingual ridge is undercut; no additional relief is required .

c) Relationship of the fulcrum line to the major connector.

       1.       When the fulcrum line is posterior to the major connector less

        relief is usually required (28 gauge, 0.013 inch to 26 gauge, 0.016 inch).

       2.       When the fulcrum line is anterior to the major connector more

       relief is usually required (26 gauge, 0.016 inch to 24 gauge, 0.020 inch).




d) Quality of supporting structures.

      1 - Periodontal status of the abutment teeth. Increased mobility of the

            abutment teeth requires more relief of the major connector.

      2 - Quality of the muco-osseous supporting tissues. Residual ridges with

      increased displaceability may require more relief of the major connector.


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                                                                 Major Connectors

    3- Bone index. Where the residual ridge exhibits a poor bone index, more
    relief may be required to compcnsate for resorptive changes occurring prior
    to anticipated relining.

e) Movement of the dento-alveolar segment.

       When the anterior teeth have a pronounced labial inclination, more relief
may be required. It may be impossible to direct the occlusal forces along the
long axes of the teeth. With such an inclination, a continued labial migration of
the teeth may occur. The labial migration may result in the major connector
impinging on the soft tissues.

        Loading force (F) applied to tooth. Force is
not directed along long axis, tooth may move
labially. Lingual bar may impinge on soft tissues




f) Lingual tori may require additional relief.




Six types of mandibular major connectors are: Mac

1. Lingual bar

2. Sublingual bar

3. Cingulum bar (continuous bar)

4. Lingual bar with cingulum bar (continuous bar)

5. Linguoplate

6. Labial bar




                                                               Mostafa Fayad - 25 -
                                                                   Major Connectors

1- Lingual bar
      The lingual bar is the simplest of the mandibular connectors, and should
be used in preference to other mandibular major
connectors whenever possible.

 Indication:

                It is the first choice major connector,
                 should be used whenever the functional
                 depth of the lingual vestibule equal or
                 exceed 7 mm. (sufficient space exists between the slightly
                 elevated alveolar lingual sulcus and the lingual gingival
                 tissue).

                If future additions of prosthetic teeth to the framework to
                 replace extracted natural teeth are not anticipated.

                Diastemas or open cervical embrasures of anterior teeth.

                Overlapped anterior teeth.

   Characteristics and Location:

   1. The lingual bar is and located on the lingual side of the alveolar ridge.

   2. It should be a half-pear shape in cross section, tapered superiorly with
      the broader and thicker portion at the inferior border.

   3. Superior inferior dimension is 3-5 mm, and it is 2 mm in thickness.

   4. Upper border of the connector should be 3-4 mm
      below and parallel to the free gingival margin to
      avoid hypertrophy to the soft tissues.(3-4mm from
      gingival margin)

   5. The inferior border should be gently rounded above the moving tissues of
      the floor of the mouth; to avoid irritation or injuring the sub adjacent
      tissues when the restoration moves.( vestibule must be 7mm at least)

   6. The bar should be relieved sufficiently but not excessively over the
      underlying tissues, Lingual tori are generously relieved when surgery is
      contraindicated.

   7. The normal thickness is a 6-gauge, it may be altered to some degree if
      additional rigidity is needed, but care must be taken to avoid tongue
      interference during speech or mastication.
                                                                 Mostafa Fayad - 26 -
                                                                    Major Connectors

Blockout and Relief of Master Cast
   (1) All tissue undercuts parallel to path of placement.
   (2) An additional thickness of 32-gauge sheet wax when the lingual surface
     of the alveolar ridge is either undercut or parallel to the path of placement.
   (3) No relief is necessary when the lingual surface of the alveolar ridge
     slopes inferiorly and posteriorly.
   (4) One thickness of baseplate wax over basal seat areas (to elevate minor
     connectors for attaching acrylic resin denture bases).
Waxing Specifications
   (1) Six-gauge, half-pear-shaped wax form reinforced by 22- to 24-gauge
   sheet wax or similar plastic pattern adapted to the design width.
   (2) Long bar requires more bulk than short bar; however, cross-sectional
   shape is unchanged.
Finishing Lines
   Butt-type joint(s) with minor connectors) for retention of denture base(s).
Advantages of the lingual bar:

    1. Simplicity and efficiency.

    2. Patient tolerance.

    3. Limited tissue coverage (hygienic).

    4. It does not contact teeth or gingival tissues allowing normal physiologic
     stimulation of the tissues.

Disadvantages

        Long lingual bars may attain some flexibility, especially if they are
         poorly constructed or designed.

        Difficult to add additional prosthetic teeth to framework.

        Framework goes from thick (at the minor connectors) to thin (at the
         bar) to thick again which is metallurgically and structurally
         complicated. The result may be weak areas in the casting with the
         potential to fracture.

Contraindications:



                                                                  Mostafa Fayad - 27 -
                                                                    Major Connectors

    1- Inadequate space between the free gingival margin and the floor
     of the mouth. Less than 7 mm exists between the marginal
     gingiva and the activated lingual frenum and floor of the mouth.

    2- Extreme lingual inclination of lower anterior teeth.

    3- Patients having high lingual frenular attachment.

    4- The presence of bilateral torus mandibularis contraindicates the use of the
     lingual bar because they interfere with the proper placement of the bar.
     Tori require adequate relief, which minimize the rigidity of the connector.

    5- The presence of an undercut on the lingual side of the ridge could cause
     gross food entrapment and discomfort in the presence of the lingual bar.

       The lingual bar functions only as a major connector. It does not provide
neither support nor indirect retention.

2- The Sublingual bar
The sublingual bar is a modification of the lingual bar.

Indications:

     1. When the lingual bar cannot be used because of a lack
      of functional depth of the lingual vestibule (depth of 5-7
      mm).

     2. Reduced height of the alveolar ridge, due to bone
      resorption or elevation of the floor of the mouth during
      functional movement.

     3. Highly attached lingual frenum.

     4. Distal extension RPD situations with sloped or parallel lingual alveolar
      ridges where a lingual bar would rotate into the lingual alveolus as the
      base area rotates tissue-ward.

     5. Diastemas and open cervical embrasures of anterior teeth.

Contraindications

         •     When lingual bar or lingual plate is sufficient.

         •     When future additions of prosthetic teeth to the framework are
                anticipated.

          Remaining natural anterior teeth severely tilted toward the lingual.

                                                                  Mostafa Fayad - 28 -
                                                                   Major Connectors

Characteristics and Location:

         The sublingual bar is essentially a lingual bar rotated 45 degrees.
          (Half-pear shape as a lingual bar except that the bulkiest portion is
          located to the lingual and the tapered portion is toward the labial).

            • it may described as having a tear drop configuration in cross
            section whose base is towards the base of the tongue.

         The superior border of the bar should be located at least 3 mm from
          the gingival margins of all adjacent teeth.

         The inferior border is located at the height of the alveolar lingual
          sulcus when the patient's tongue is slightly elevated. This
          necessitates a functional impression of the lingual vestibule to
          accurately register the height of the vestibule.

         The sublingual bar is located on the alveo-lingual sulcus inferior to
          the usual site of the lingual bar; extending over and parallel to the
          anterior floor of the mouth.

Blockout and Relief of Master Cast

     (1) All tissue undercuts parallel to path of placement.

     (2) An additional thickness of 32-gauge sheet wax when the lingual surface
     of the alveolar ridge is either undercut or parallel to the path of placement.

     (3) One thickness of baseplate wax over basal seat areas (to elevate minor
     connectors for attaching acrylic resin denture bases).




Waxing Specifications

     (1) Six-gauge, half-pear-shaped wax form reinforced by 22- to 24-gauge
     sheet wax or similar plastic pattern adapted to design width.

     (2) Long bar bulkier than short bar; however, crosssectional shape
     unchanged.Finishing Lines Butt-type joint(s) with minor connectors) for
     retention of denture base(s).

Advantages of the sublingual bar

    1. It is well tolerated by most of the patients.


                                                                Mostafa Fayad - 29 -
                                                                  Major Connectors

    2. It does not cover the teeth or tissues. It permits exposure of the gingival
     tissue and the lingual surfaces of anterior teeth allowing for the natural
     physiologic stimulation of the gingiva.

    3. Proper oral hygiene conditions could be maintained as the sublingual bar
     allows for proper tooth and tissue cleaning.

    4. Some dentists suggested the use of sublingual bar because the under side
     of the tongue is relatively sparsely provided with tactile receptors.

   5. More rigid than a lingual bar in the horizontal plane.

Disadvantages:

       A functional impression of the vestibule is required to accurately register
the position and contour of the vestibule.

To determine the relative height of the floor of the mouth:


a) The first method is to measure the height of the floor of the mouth in relation
to the lingual gingival margins of adjacent teeth with a periodontal probe.
During these measurements, the tip of the patient's tongue should be just lightly
touching the vermilion border of the upper lip. Recording of these measurements
permits their transfer to both diagnostic and master casts, thus ensuring a rather
advantageous location of the inferior border of the major connector.


b) The second method is to use an individualized impression tray having its
lingual borders 3 mm short of the elevated floor of the mouth and then to use
an impression material that will permit the impression to be accurately molded
as the patient licks the lips. The inferior border of the planned major connector
can then be located at the height of the lingual sulcus of the cast resulting from
such an impression. Of the two methods, we have found the measuring of the
height of the floor of the mouth to be less variable and more clinically
acceptable.


3- Mandibular cingulum bar (continuous bar)

Indication

                                                                Mostafa Fayad - 30 -
                                                                      Major Connectors

       Where there is insufficient room for the lingual bar, between gingival
margin and the floor of the mouth, and unless the periodontal health is well
maintained.

          The teeth should have good mesiodistal contact with sufficient crown
length.

Kennedy bar

It is known as secondary lingual bar, continuous bar or cingulurn bar.

It is used alone or in conjunction with a lingual bar forming the double lingual
bar, to add to the strength and rigidity of the denture.

Kennedy bar is not indirect retainer by itself.

Contraindications

    (1) Anterior teeth severely tilted to the lingual.

    (2) When wide diastemata exist between the mandibular anterior teeth and
    the cingulum bar would objectionably display metal in a frontal view.

Characteristics and Location:

    (1) Thin, narrow (3 mm) metal strap located on cingula of anterior teeth,
    scalloped to follow interproximal embrasures with inferior and superior
    borders tapered to tooth surfaces.

    (2) Originates bilaterally from incisal, lingual, or occlusal rests of adjacent
    principal abutments.

Blockout and Relief of Master Cast

           No relief for cingulum bar except blockout of interproximal spaces
    parallel to the path of placement.

Waxing Specifications

          Cingulum bar pattern formed by adapting two strips (3 mm wide) of
    28-gauge sheet wax, one at a time, over the cingula and into interproximal
    embrasures.

Finishing Lines

          Butt-type joint(s) with minor connectors for retention of denture base(s).

Advantages

    Permits exposure of the gingival tissue that allows natural stimulation but
                                                                   Mostafa Fayad - 31 -
                                                                  Major Connectors

    It eliminates the need of indirect retainer,

Disadvantages

    The metal bulk of the bar may be disadvantage and esthetic may be
     compromised, if spacing is present.

    The open space may traps food and may exacerbate gingival trauma and it
     may be objectionable to the tongue.

4- The Double lingual bar:
  The double lingual bar is a major connector, which consists of a lingual bar
  and a cingulum bar (Kennedy bar).

Indication

      1-When indirect retention is required.

      2-When periodontally affected teeth that require splinting are present.

      3- When a linguoplate is indicated but the axial alignment of anterior
      teeth is such that excessive blockout of interproximal undercuts would be
      required.

      4- When wide diastemata exist between mandibular anterior teeth and a
      Linguoplate would objectionably display metal in a frontal view.

Contraindications:

      - When the teeth have short clinical crowns or inclined lingually.

Characteristics and Location:

    a- The upper bar

          1. The Kennedy bar is a thin, narrow, scalloped, 3 mm wide metal
          strap which located on or slightly above the cingulae of anterior teeth.

          2. It should be half-oval in cross section and approximately 2 to 3
          mm. high and 1mm. thick at its greatest diameter.

          3. It is joined to the lingual bar via two rigid minor connectors, which
          are located in the interproximal spaces, usually between the canines
          and first premolars.

          4. Two supporting rests must be placed one on each end of the
          Kennedy bar. These rests prevent settling of the bar during function,


                                                                Mostafa Fayad - 32 -
                                                                    Major Connectors

          thus preventing laceration of the gingiva and ulceration of the mucosa
          covering the floor of the mouth.

   b- The lower bar

         It should have the same design as a single lingual bar, half pear-
         shaped in cross section with the greatest diameter at the inferior
         margin.

Blockout and Relief of Master Cast

      (1) Lingual surface of alveolar ridge and basal seat areas same as for
      lingual bar.

      (2) No relief for continuous bar except blockout of interproximal spaces
      parallel to path of placement.

Waxing Specifications

      (1) Lingual bar major connector component waxed and shaped same as
      lingual bar.

      (2) Continuous bar pattern formed by adapting two strips (3 mm wide) of
      28-gauge sheet wax, one at a time, over the cingula and into interproximal
      embrasures.

Finishing Lines

      Butt-type joint(s) with minor connectors) for retention of denture base(s).

Advantages of the double lingual bar:

  1. The open space allows natural stimulation of gingival tissue.

  2. Provides stabilization against lateral forces.

  3. The configuration of this bar adds to the strength and rigidity of the
     denture.

  4. Proper distribution of the stresses acting on the partial denture to all teeth.

  5. Helps in splinting of periodontally affected teeth.

  6. The double lingual bar acts as an indirect retainer through its terminal
     rests.

  7. The continuous bar may be considered with excessive interproximal
     undercuts and the linguoplate major connector cannot be used.

  8. It may be modified to circumvent a diastema between teeth.

                                                                  Mostafa Fayad - 33 -
                                                                   Major Connectors

Disadvantages:

   1. It is objectionable to the tongue and thus poorly tolerated by patients.

   2. If the open space is insufficient may collect food and produce tissue
    irritation.

   3. May cause phonetic problems.

6- Lingual Plate (closed Kennedy bar)
                 The lingual plate is the most rigid
          mandibular major connector. It provides better
          bracing than do other mandibular connectors. It
          also provides cross-arch stabilization and
          splinting for weak teeth.

Indications:

        1- When the space available is insufficient for the construction of a rigid
           lingual bar as in cases with high lingual frenular attachment or high
           floor of the month. May be used when the functional depth of the
           lingual vestibule is less than 5 mm

        2 When additional strength is required in cases having mandibular tori
          which are contraindicated for surgical removal.

        3- In distal extension bases where indirect
           retention is required.

        4- In Kennedy class I cases exhibiting excessive
           loss of the residual ridges where the lingual
           plate can provide resistance against horizontal
           movement of the partial denture.

        5- When future replacement of teeth is expected.

        6- In patients intolerable to lingual bars.

        7. It is particularly useful in stabilizing periodontally weakened teeth

Characteristics and Location:

         It is an extended lingual bar that crosses the relieved gingival margin to
         terminates above the cingulae of anterior teeth or survey line of
         posterior teeth in the form of a plate.

      1. Half-pear shaped with bulkiest portion inferiorly located.


                                                                 Mostafa Fayad - 34 -
                                                             Major Connectors

2. Thin metal apron extending superiorly to contact cingula of anterior
   teeth and lingual surfaces of involved posterior teeth at their height of
   contour.

3. Apron extended interproximally to the height of contact points, i. e.,
   closing interproximal spaces.

4. Scalloped contour of apron as dictated by interproximal blockout.

5. Superior border finished to continuous plane with contacted teeth.

6. Inferior border at the ascertained height of the alveolar lingual sulcus
   when the patient's tongue is slightly elevated.

7. The superior border must positively contact the lingual surfaces of
   the teeth above the survey line to avoid food entrapment.

8. The superior border should be thin, knife edged scalloped border,
   sharply projected between the teeth, and should never be placed above
   the middle third of the teeth.

9. The inferior border of the lingual plate is a half-pear shaped placed at
   the functional limit of the floor of the mouth.

10. Adequate block-out is required for teeth and soft tissue undercuts.

11. Gingival margins should be relieved to avoid gingival irritation.
    Excessive relief should be avoided because tissues tend to fill a void,
    resulting in the overgrowth of abnormal tissue. The amount of relief
    used, therefore, should be only the minimum necessary to avoid
    gingival impingement

12. The lingual plate must always be supported at each end by rests, to
    provide indirect retention.

13. when a single diastema exists a notched lingual plate could be used to
    avoid display of metal.



       Interrupted linguoplate

       When the anterior teeth are quite spaced and the patient
strenuously objects to metal showing through the spaces,the linguoplate
can then be constructed so that the metal will not appreciably show
through the spaced anterior teeth. Rigidity of the major connector is not
greatly altered.


                                                          Mostafa Fayad - 35 -
                                                                    Major Connectors

             However, such a design may be as much of a food trap as the
      continuous bar type of major connector.

Blockout and Relief of Master Cast

    (1) All involved undercuts of contacted teeth parallel to the path of
    placement.

    (2) All involved gingival crevices.

    (3) Lingual surface of alveolar ridge and basal seat areas the same as for a
    lingual bar.

Waxing Specifications

    (1) Inferior border—6-gauge, half-pear-shaped wax form reinforced with
    24-gauge sheet wax or similar plastic pattern.

    (2) Apron—24-gauge sheet wax.

Finishing Lines

    Butt-type joint(s) with minor connectors for retention of denture base(s).

Advantages

    1. The most rigid mandibular major connector.

    2. It gives indirect retention to the partial denture.

    3. Deflect food from impacting on lingual tissues.

    4. Provide resistance against horizontal or lateral forces.

    5. Permits the replacement of lost tooth without remaking the PD.

    6. Help in splinting and prevent super-eruption of the anterior teeth.

    7. Patients frequently consider the lingual plate to be more comfortable and
    more acceptable for tongue comfort and ease in phonetics than the lingual
    bar.

        The lingual palate is the most rigid mandibular connector, and provides
        more support and stabilization than do the other connectors.

      Disadvantages of the lingual plate:

        1. It prevents normal physiologic stimulation of the gingival tissue
        and the self cleansing action of the teeth by the saliva and tongue.


                                                                  Mostafa Fayad - 36 -
                                                                   Major Connectors

          2. Encourages plaque formation, and may contribute to caries and
          periodontal disease in patient with poor oral hygiene.

          3. Covers more tooth and gingival tissues than other mandibular
             major connectors.

      Contraindications:

           A lingual bar may be used.

           Overlapped anterior teeth where the undercuts in the area of the
            superior edge of the plate can not be removed. Frequently this
            criteria can not be met and a lingual plate which will have small
            gaps between the superior edge of the plate and the teeth must be
            used.

           Lingually inclined teeth.

           Diastemas, unless the lingual plate can have slots in it to avoid the
            display of metal.

           Open cervical embrasures where the plate would be visible.

      The linguoplate does not in itself serve as an indirect retainer. When
indirect retention is required, definite rests must be provided for this purpose.
Both the linguoplate and the cingulum bar should ideally have a terminal rest at
each end regardless of the need for indirect retention. However, when indirect
retainers are necessary, these rests may also serve as terminal rests for the
linguoplate or continuous bar.
6-Labial and buccal bars:
      The labial bar connector situated in the labial or buccal sulcus.

Indications:

   1. In case of extreme lingual inclination of mandibular anterior and
      premolar teeth that prevents the use of a lingual major connector.

   2. When large lingual tori exist and surgery is precluded.

   3. When severe and abrupt lingual tissue undercuts make it impractical to
      use a lingual bar or lingual plate major connector.
Design:



                                                                 Mostafa Fayad - 37 -
                                                                    Major Connectors

   1. It should be made with greater thickness and bulk than a lingual bar to
      counteract the increased flexibility due to increased length.

   2. It is half-pear shaped with bulkiest potion located inferiorly, runs across
      the labial and buccal mucosa. Superior border tapered to soft tissue
      located at least 4 mm. below the gingival margin.

   3. Relief is required beneath the bar. It must be
      relieved over the canine eminence.

   4. It is half pear shaped in cross-section.

   5. Labial vestibule should be adequate to allow the
      superior border to be place at leas 3-4 mm below
      the free gingival margins.

   6. Inferior border located in the labial-buccal vestibule at the juncture of
      attached (immobile) and unattached (mobile) mucosa.
Blockout and Relief of Master Cast

  (1) All tissue undercuts parallel to path of placement, plus an additional
  thickness of 32-gauge sheet wax when the labial surface is either undercut or
  parallel to the path of placement".

  (2) No relief necessary when the labial surface of the alveolar ridge slopes
  inferiorly to the labial or buccal.

  (3) Basal seat areas same as for lingual bar major connector.



Waxing Specifications

   (1) Six-gauge, half-pear-shaped wax form reinforced with 22- to 24-gauge
   sheet wax or similar plastic pattern.

   (2) Long bar necessitates more bulk than short bar; however, cross sectional
   shape unchanged.

   (3) Minor connectors joined with occlusal or other superior components by a
   labial or buccal approach.

   (4) Minor connectors for base attachment joined by a labial or buccal
   approach.

Finishing Lines

      Butt-type joint(s) with minor connector(s) for retention of denture base(s).

                                                                  Mostafa Fayad - 38 -
                                                                Major Connectors

Advantages:

      The labial bar obviates the need for surgical
       intervention to permit use of a lingual major
       connector.

      It solves the problem of severely inclined teeth
       and avoids surgical intervention to remove a
       large torus.

Disadvantages:

1.       The labial bar usually lacks sufficient rigidity.

2.      Labial vestibular depth must be adequate especially in the presence of
gingival recession.

3.       The least comfortable mandibular major connector.

4.      It distorts the lower lip and the presence of the metal between the
gingival tissue and the lip causes patient discomfort.

5.       Difficult to add prosthetic teeth to framework.

Contraindications:

      When lingual major connector may be used.

      Facial tori or exostoses.

      The facial alveolar ridge is undercut.

      High facial muscle attachments which would result in less than 3 mm
       of space between the superior edge of the labial bar and the marginal
       gingiva of the teeth.

7- The Swing Lock Partial Denture:
         The hinged continuous labial bar called the Swing-lock design partial
         denture is a modification of the labial bar.

     Indications

           1- Missing key abutments such as a canine.

           2- Unfavorable tooth contours: When existing tooth contours
           (uncorrectable by recontouring with appropriate restorations) or
           excessive labial inclinations of anterior teeth prevent conventional
           clasp designs,

                                                              Mostafa Fayad - 39 -
                                                                 Major Connectors

        3- Unfavorable soft tissue contours. Extensive soft tissue undercuts
        may prevent proper location of component parts of a conventional
        removable partial denture

        3- Periodontally affected Teeth with questionable prognosis: The
        Swing lock partial denture provides splinting.

   Design

        It is consists of a labial or buccal bar that is connected to the major
      connector by a hinge on one end and a latch at the other end.

         The labial bar is connected to a lingual
      plate major connector by a hinge device at
      one end and a locking device at the other
      end. Vertical minor connectors arise from
      the labial bar and may touch the anterior
      teeth either below or above the survey line.

         Support is provided by multiple rests on the remaining natural teeth.
      Stabilization and reciprocation are provided by a linguoplate contacting
      the remaining teeth and are supplemented by the labial bar with its
      retentive struts. Retention is provided by a bar type of retentive clasp
      arms projecting from the labial or buccal bar and contacting the
      infrabulge areas on the labial surfaces of the teeth.

   Advantages:

    1- Helps in providing both retention and stabilization.

    2- The labial bar together with the lingual plate provides the required
       rigidity, thus the labial bar does not require much bulk.

   Contraindications

      1- Poor oral hygiene.

      2- The presence of shallow buccal or labial vestibule.

      3- The presence of high labial frenal attachment




8- Split lingual major connector:( SPLIT MANDIBULAR)
                                                               Mostafa Fayad - 40 -
                                                                  Major Connectors

           It is a flexible connector, used where some stress release from the
     abutment teeth is desired. Inevitably, this stress broken design is a more
     complex construction and thus more costly, and may also pose greater
     demands on plaque control and be less well tolerated by the patient.

   Indications.

         a. May be used where some stress release from the abutment teeth is
        desired through the major connector.

         b. May be used in place of stress releasing clasps or stress directors.

   Design:

         a. May be fabricated in a single casting or in combination with a
        soldered wrought wire of large diameter.

          b. Due to the stress concentration, there may be a tendency to fracture
        at the union of the bars.

9- Dental bar
          On occasions, there is insufficient room between gingival margin and
   floor of the mouth for either a sublingual or lingual bar. A lingual plate
   should be avoided wherever possible because it might well tip the delicate
   balance between health and disease in favour of the latter.

          An alternative connector, where the clinical crowns are long enough,
   is the dental bar. Patient tolerance inevitably places some restriction on the
   cross-sectional area of this connector and thus some reduction in rigidity
   may have to be accepted.




                                                               Mostafa Fayad - 41 -
                                                                    Major Connectors




      Sequence of design considerations for a mandibular major connector

      Step 1: Outline the basal seat areas on the diagnostic cast

      Step 2: Outline the inferior border of the major connector

      Step 3: Outline the superior border of the major connector

      Step 4: Connect the basal seat area to the inferior and superior borders of
the major connector, and add minor connectors to retain the acrylic resin denture
base material




Selection of maxillary major connector

1- Function:

       Maxillary: support, retention and stability: The width of the major
    connector may be varied according to the amount of support required.
    e,g anterior and posterior palatal strap when good abutment support
    ,Complete palatal coverage when mucosal support is desired

      Mandibular: need for indirect retention


                                                                Mostafa Fayad - 42 -
                                                                  Major Connectors

2- Anatomical consideration :

     Maxillary: palatal tori

     Mandibular:

               Lingual tori

               Lingual gingival recession

               High lingual frenal attachment

               Inclination of remaining anterior teeth

3- Hygiene:

       oral hygiene is better with lingual bar

4- Rigidity:

       The rigidity of the major connector may be increased by varying the
thickness or by placing the metal in two different planes.

5- Patient acceptability:

       Strap or plate type major connectors, because they can be made thinner,
usually have a greater patient acceptance than the bar types. Some patients may
find the increased palatal coverage uncomfortable due to alterations in gustatory,
thermal or tactile perception. Generally, posterior or mid palatal straps are less
objectionable than anterior palatal straps or bars.

6- Location of edentulous area:

       The major connector must connect the components of the partial denture.

7- Anticipated loss of natural teeth

8- Location of fulcrum line:

       The portion of the major connector located posterior to the indicated
fulcrum line may provide muco-osseous support for the RPD.




                                                                Mostafa Fayad - 43 -
                                                                       Major Connectors




Indications for Maxillary Major Connectors:
    a) If the periodontal support of the remaining teeth is week, a wide palatal
    strap or completely palatal coverage is indicated.

    b) If the remaining teeth have adequate periodontal support and little
    additional support is needed, a palatal strap or double palatal bar can be
    used.

    c) For long-span distal extension bases, a closed horseshoe or complete
    palatal coverage is indicated.

    d) When anterior teeth must be replaced, a horseshoe, closed horseshoe,
    or completely palatal coverage may be used.

    e) If a torus is present and is not to be removed, a horseshoe, closed
    horseshoe, or anteroposterior palatal bar may be used.

    f) A single palatal bar is rarely indicated.

    g) The combination anterior-posterior connector design may be used with
    any Kennedy class of partially edentulous arch. It is used most frequently in
    Classes II and IV, whereas the single wide palatal strap is more frequently
    used in Class III situations. The palatal plate-type or complete coverage
    connector is used most frequently in Class I situations.

Class 1 palatal plate-type

      Class I partially edentulous arches with residual ridges that have undergone
       little vertical resorption and will lend excellent support: SINGLE BROAD
       PALATAL

      Class I and II arches in which excellent abutment and residual ridge support
       exists, and direct retention can be made adequate without the need for indirect
       retention. ANTERIOR-POSTERIOR STRAP-TYPE

      only some or all anterior teeth remain. COMPLETE PALATAL COVERAGE

      Class I arch with one to four premolars and some or all anterior teeth remaining,
       and abutment support is poor and cannot otherwise be enhanced; residual ridges
       have undergone extreme vertical resorption; direct retention is difficult to
       obtain. COMPLETE PALATAL COVERAGE




                                                                    Mostafa Fayad - 44 -
                                                                                 Major Connectors

Class 2 : ANTERIOR-POSTERIOR STRAP

        Long edentulous spans in Class II, modification 1 arches. ANTERIOR-
         POSTERIOR STRAP

        Class II arch with a large posterior modification space and some missing
         anterior teeth. COMPLETE PALATAL COVERAGE

Class 3: single wide palatal strap

        Bilateral edentulous spaces of short span in a tooth-supported restoration:
         SINGLE PALATAL STRAP



Class 4 : ANTERIOR-POSTERIOR STRAP

        Class IV arches in which anterior teeth must be replaced with a removable
         partial denture. ANTERIOR-POSTERIOR STRAP

----------------------------------------------------------------------------

        V- or U-shaped palates: SINGLE BROAD PALATAL

        No interfering tori. SINGLE BROAD PALATAL

        absence of a pedunculated torus. COMPLETE PALATAL COVERAGE

        Inoperable palatal tori that do not extend posteriorly to the junction of the hard
         and soft palates. ANTERIOR-POSTERIOR STRAP

        inoperable tori extend to the posterior limit of the hard palate. U-SHAPED
         PALATAL



Indications, for Mandibular Major Connectors:

          1-For a tooth-supported, the lingual bar is normally the mandibular
          major connector of choice

          2- For long-span edentulous ridges in which there is no posterior
          abutment tooth and indirect retention is needed ,the lingual plate is
          indicated .

          3- When the anterior teeth have reduced periodontal support and need
          stabilization, the lingual plate or double lingual bar may be used .

          4- When mandibular tori are present, or when a high lingual frenum is
          present, a lingual plate must be used.

                                                                               Mostafa Fayad - 45 -
                                                                              Major Connectors

           5- For patient who have large inter-proximal spaces that cause esthetic
           problems by the display of the metal of a lingual plate ,a double lingual
           bar may be indicated.

           6- The labial bar is rarely indicated.

         Sufficient space exists between the slightly elevated alveolar lingual sulcus and
          the lingual gingival tissue. MANDIBULAR LINGUAL BAR

         height of the floor of the mouth in relation to the free gingival margins will be
          less than 6 mm MANDIBULAR SUBLINGUAL BAR

         alveolar lingual sulcus so closely approximates the lingual gingival crevices
          MANDIBULAR LINGUOPLATE

         periodontally weakened teeth in group function to furnish support to the
          prosthesis and to help resist horizontal (off vertical) rotation of the distal
          extension type of denture. MANDIBULAR LINGUOPLATE
         future replacement of one or more incisor teeth MANDIBULAR LINGUOPLATE

         linguoplate is indicated but the axial alignment of anterior teeth is such that
          excessive blockout of interproximal undercuts would be required.
          MANDIBULAR LINGUAL BAR WITH CONTINUOUS BAR
         wide diastemata exist between mandibular anterior teeth and a Linguoplate
          would objectionably display metal in a frontal view. MANDIBULAR LINGUAL
          BAR WITH CONTINUOUS BAR
         lingual plate or sublingual bar is otherwise indicated but the axial alignment of
          the anterior teeth is such that the excessive blockout of interproximal undercuts
          would be required. CINGULUM BAR
         lingual inclinations of remaining mandibular premolar and incisor teeth cannot
          be corrected LABIAL BAR
         severe lingual tori cannot be removed LABIAL BAR
         severe and abrupt lingual tissue undercuts make it impractical to use a lingual
          bar or lingual plate LABIAL BAR
class 1

Class I arch residual ridges have undergone such vertical resorption that they will offer
only minimal resistance to horizontal rotations of the denture through its bases.
MANDIBULAR LINGUOPLATE



                                                                            Mostafa Fayad - 46 -
                                                                   Major Connectors




                         MINOR CONNECTORS


       A minor connector is that part of removable partial denture, which joins
the major connector or the partial denture base to other components of the
prosthesis.

        A minor connector is a component that links the major connector or base
and other components of the partial denture such as rests, indirect retainers and
clasps.

Design Specifications:

Minor connectors that contacts the axial tooth surfaces or contacts the guiding
plane surfaces of the abutment teeth whether as a connected part to the clasp
assembly or as a separate entity should fulfill the following requirements:

  1. Minor connectors must have sufficient bulk to be rigid.

   A typical minor connector is 2mm width and 1.5mm thickness
   in cross section.

  2. The bulk of the minor             connectors    must   be     as
     unobjectionable as possible.

  3. Where the minor connector joins a rest, a minimum metal thickness of 1.5
     mm at the junction is required for base metal alloys (2 mm for gold
     alloys).

  4. Minor connector contacting the axial surface of an abutment should
     contact guiding plane surfaces and should never be located on convex
     surfaces (why?).

  5. Minor connector conforms to the interdental embrasure, (as in case of
     embrasure clasp or that used as indirect retainer) passing vertically from
     the major connector and covers as little of the gingival tissues as
     possible.

  6. The surface of metal facing the tongue should be smooth and beveled. The
     minor connector should be thickest toward the lingual surface and
     tapering toward the contact area, to provide space for the arrangement of



                                                                 Mostafa Fayad - 47 -
                                                                     Major Connectors

      teeth. In this case they are triangular in shape, the base of the triangle faces
      the tongue and the apex lies toward the lingual contact area of teeth.

  7. Should exhibit minimal gingival coverage; the lingual minor connector
     should cross the gingival margins directly, joining the major connector at
     rounded right angle

  8. The junction between minor connector and major connector should be
     rounded rather than angular. Sharp angles should be avoided and
     spaces should not exist for the trapping of food debris.

  9. The marginal gingiva crossed by any minor connectors should be relieved
     especially in tooth-mucosa borne dentures.

  10. There should be a minimum of 5 mm space between any two neighboring
      minor connectors or from other vertical components.

  11. Should be highly polished to minimize plaque accumulation.



Functions of minor connectors:

  1. Joining different parts of the prosthesis to the major connector, or to
     denture bases.

  2. Transfer and distribute functional stresses to the abutment teeth.

  3. Transfer the effect of retainers, rests, and stabilizing units to the denture.

  4. Minor connectors contacting guiding planes add to the retention and
     stability of dentures (How).



Types of minor connectors:



I-Minor Connectors That Joint Indirect Retainers or Auxiliary Rests to The
Major Connector:

        It is generally arising from the major connector. They should form a right
angle with the major connector, but the junction should be a gentle curve rather
than a sharp angular connection. The minor connector should be designed to lie
in the embrasure between teeth to disguise its bulk as mush as possible.

      a- Proximal Minor Connectors


                                                                   Mostafa Fayad - 48 -
                                                                 Major Connectors

       Proximal minor connectors contact an abutment tooth adjacent to an
edentulous space. Proximal minor connectors are usually termed Proximal
Plates but are sometimes call Guiding Plates, Struts and Finishing Plates.

Design

    Proximal plates extend from the proximal facial line angle to, or slightly
     past, the proximal lingual line angle of the abutment tooth. They are thin
     mesio-distally and taper slightly toward the occlusal (incisal).

    They extend from the occlusal/incisal of the tooth to the major connector.
     The junction of rests and clasp arms with proximal minor connectors, and
     proximal minor connectors to major connectors are rounded right angles.

    They should be broad bucco-lingually to provide strength and thin mesio-
     distally to minimize encroachment on the saddle area. This will enable the
     artificial teeth to be positioned closely to the abutment tooth to achieve
     satisfactory aesthetics.

    They extend cervically and contact the mucosa of the ridge crest for 2-3
     mm.

    The part of the proximal minor connector which contacts the ridge crest is
     called the Foot of the proximal plate



Functions of Proximal plates

    Connect rests and clasp arms to the major connectors,

    Provide frictional retention by contact with guiding planes on the teeth,

    Help reciprocate the force of the direct retainer,

    Unite the dental arch by substituting for lost proximal tooth contacts

    Distribute forces (bracing).

    Contact proximal guiding planes on the teeth thus helping to determine
     the path of placement of the RPD,

    Prevent food impaction between the proximal surface of the tooth and the
     RPD,

    Provide a definite finish line for the junction of the denture base and
     major and minor connectors,


                                                               Mostafa Fayad - 49 -
                                                                   Major Connectors




b- Embrasure Minor Connectors
        If the direct retainer or auxiliary rest to be placed between two adjacent
teeth, the minor connector must be positioned in the lingual embrasure between
the two teeth. Using this triangular space for the metal results in sufficient bulk
without encroaching on tongue space.

Design

    It should be designed into the lingual embrasure between two adjacent
     teeth to disguise bulk as much as possible.

    They extend from the occlusal, incisal or cingulum surface of the tooth to
     the major connector. They join the major connector in a rounded right
     angle to avoid sharp corners and they taper slightly toward the occlusal
     (incisal).

    Triangular shaped in cross section

    Relief placed so connector not directly on soft tissue

    Contact teeth above height of contour, so prevents wedging & tooth
     mobility

Functions of embrasure minor connectors

    • Connect rests and clasp arms to the major connectors,

    • Provide frictional retention by contact with guiding planes on the teeth,

    • Help reciprocate the force of the direct retainer,

    • Unite the dental arch by substituting for lost proximal tooth contacts

    • Distribute forces (bracing).

    • Contact inter-proximal guiding planes thus helping to determine the path
    of placement of the RPD,

c- Surface Minor Connectors
      Surface minor connectors are located on the lingual surface of incisors
and canines. They connect lingual rests to the major connector.

                                                                 Mostafa Fayad - 50 -
                                                                     Major Connectors

Design

    Their junction with the major connector is a rounded right angle and they
     taper toward the occlusal (incisal).

    The lateral borders extend into the proximal embrasures to hide these
     edges from the tongue.

    The surface minor connector may be penetrated by the tip of the lingual
     cingulum rest preparation. This "open" design facilitates fitting the
     framework and cleaning the tissue surface of the minor connector.
     Another modification of the surface minor connector is a "finger rest" in
     which the rest extends from the proximal or embrasure minor connector
     into the rest preparation.



Radford modification:

   A modification of the conventional removable partial denture minor
connector has been proposed by Radford.

 He limits the application of this variation in minor connector design to the
maxillary arch only.

   He suggests placing the minor connector in the center of the lingual
surface of the maxillary abutment tooth.

  Advantages:

         reduces the amount of gingival tissue coverage

         provides enhanced guidance for the PD during insertion and removal

         increased stabilization against horizontal and rotational forces.

  Disadvantages:

         encroach on the tongue space and provide more obvious borders and a
greater potential space between the connector and the abutment for food
entrapment.



II-Minor connectors that serve as approach arm for vertical projection or
bar-type clasp:

    It is the only one that is not required to be rigid.


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                                                                     Major Connectors

    It supports a direct retainer (clasp) that engages an undercut on a tooth;
     from below rather than above.

    It approaches the tooth from the gingival margin. It should have a smooth,
     even taper from its origin to its terminus. It must not cross a soft tissue
     undercut.

    It must be relieved from the tissue to avoid tissue injury.




III-Minor connectors that join the denture base to the major connector:

(Denture Base Retention (Grid-work) minor Connector) see denture base

        it is the means by which the plastic denture base is mechanically attached
to the framework.

  It may be:

a) Open Lattice work construction.

b) Mesh construction.

c) Bead, wire, or nail-head minor connectors (used with a metal base).




RELATIONSHIP OF MINOR CONNECTORS TO THE TOOTH
SURFACE

       If the tooth surface is not entirely parallel to the path of placement and
removal of the RPD, a space will be created between the minor connector and
the tooth surface below the height of contour.

      There is a difference of opinion as to how large this space should be.

      1- Kratochvil suggest that there should be no space between the proximal
      minor connector, tooth and ridge to prevent hypertrophy of tissue into the
      space.

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                                                                              Major Connectors

        2- Others suggest that the space should be kept large so that it may be
        easily cleaned by the tongue while the RPD is in the mouth ("self-
        cleansing design") and thus less likely to cause periodontal damage and
        mucosal irritation.

       3- Actually the space is usually determined by the anatomy of the tooth,
its angulation in relation to the path of placement and removal of the RPD and
esthetic considerations.

The dentist has little control over the size of this space unless the tooth is going
to be restored with a surveyed crown. And, other factors are much more
important in the success of RPD treatment than the space between the proximal
plate and the tooth.


-

Variations in the space between the proximal minor connectors
and the abutment tooth ,

a) minimum space to prevent tissue hypertrophy into the space,

b) “self-cleansing” design,

c) space determined by anatomy of tooth, angulation of the tooth
relative to the path of placement and removal of the RPD, and
limitation of the amount the tooth can be reshaped to decrease the
space

-




State rules of thumb for the form and length of minor connectors connecting acrylic resin
denture bases to major connectors.

Give a rule of thumb for how far the minor connector attaching the resin base to the major
connector should extend posteriorly.

The thickness of impression material when rubber-base material is used should be about 3 mm
(1/8 inch) for accuracy and stability. Does this equally apply to a hydrocolloid impression
material? If not, give a rule of thumb for the desired thickness of the hydrocolloid material in
the impression.



Sufficient relief must be provided beneath a major connector to avoid impingement and/or
displacement of soft tissue resulting in an inflammatory response. What is meant by the word

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                                                                               Major Connectors
relief? Rationalize planned relief for a lingual bar and give quantitative rules of thumb that
depend on the contour of the anterior, lingual alveolar ridge.

There are definite rules of thumb for the location of the anterior and posterior borders of all
palatal major connectors. Describe the relationship of the borders to rugae, junction of hard
and soft palates, gingival crevices, pterygomaxillary notches, and palatal tori.




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                                                                       Direct retainers


                               Retention Of Partial Denture

Retention is the resistance of the partial denture to vertical displacement away from
the tissues.
Retention of an RPD can be achieved by:


-   Using the inherent physical forces which arise from coverage of the mucosa by the
denture.
-    Physiologic factors: Harnessing the patient’s muscular control acting through the
polished surface of the denture.
- Using mechanical means such as clasps which engage undercuts on
the tooth surface.




A] Physical means of retention:
1-Adhesion; is the attraction of the saliva to the denture and the tissues.
2-Cohesion; is the attraction of saliva molecules to each other.
3-Interfacial surface tension; is the attraction of the surface molecules.
4-Atmospheric pressure; Which is dependent on a border seal and results in a partial
vacuum beneath the denture base when a dislodging force is applied.
The difference between the greater pressure acting on the polished surface of the
denture and the lesser pressure acting on the fitting surface causes a positive force,
which helps in retaining dentures.
The effect of atmospheric pressure in retaining partial dentures is limited because a
complete border seal cannot be obtained as can be accomplished with complete
dentures.
5 -Gravity; The effect of gravity tends to seat lower dentures, but displace upper
dentures.
6- Plastic molding between tissues / denture polished surfaces aid to little extent in
retention of partial denture




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The effect of physical forces is less applicable to lower dentures than upper denture
because:
           a- Lower dentures have less surface area.
           b- Lower dentures are bathed in saliva.
           c- Lower major connectors are relieved from the underlying tissues
           contrary to upper major connectors that are well adapted and their borders
           are beaded against the underlying tissues.
           d- Strong movements of the tongue tend to break the seal in lower
           dentures.


B]The Physiological means of retention:


1- The physiologic molding of the tissues around the polished surfaces of the denture
helps to perfect the border seal.
2- Neuromuscular control: The patient ability to control the denture with the lips,
cheeks, and tongue can be a major factor in the retentiveness of the denture.


C] Mechanical means of retention
        The primary retention of the removable partial denture is accomplished
    mechanically by placing retaining elements on the abutment teeth, which are
    achieved by:


1. Direct retainers:
           The components of partial denture that are used primarily to retain the
     denture and resist vertical dislodging forces applied to it.


            Types of direct retainers:-

       a- Intracoronal retainer.

           Usually called as an internal attachment or a precision attachment.
           It is developed by Dr Herman E.S.Chayes in 1906.
      b- Extracoronal retainers.
          A-Clasps: which are metal projections engaging abutments to hold


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            denture in place.
             B- Attachments:
                     These are ready or tailor made, male and female components.
             One component is fixed to the abutment, and the other attached to the
             denture. They are either extra coronal or intracoronal attachment.


2. Indirect retainers:
              They are components of partial denture that are used to resist vertical
       displacement of a distant part of the denture.
3. Frictional fit between the natural and artificial teeth.
4. Parts of the denture engaging tooth undercuts.
5. Parts of the denture engaging tissue undercuts.




                                  Clasp Retainers

        A Clasp is a metal projection of the partial denture engages the external
  surface of an abutment in an area cervical to the height of contour (undercut) to
  retain the partial denture. It is also called an extra-coronal retainer.
        It is first appeared in dental literature in 1899 by G.V.Bonwill



Components of a clasp:

        A classic clasp consists of the following parts:
1-A minor connector
(Called truss arm, tail, tang, upright arm, clasp stalk )
        It is a rigid part of the clasp placed on the proximal surface of abutment tooth
        extending from the marginal ridge to the junction between the middle and
        gingival third of the abutment crown..
     Functions: -It Joins clasp to framework.
                     - It acts as a proximal plate dictating the path of insertion .
                     - Bracing and stabilization of the denture.
2-A rest:

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It is a part of the clasp placed on prepared occlusal, lingual or incisal surfaces of teeth.
    Function:! It supports the denture.
3-A retentive clasp arm:
               The retentive clasp arm of the occlusally approaching clasp comprises a
         rigid part located above the height of tooth contour to provide bracing then
         tapers and ends in a flexible terminal, which engages an undercut area below
         the height of tooth contour. The terminal end of the clasp arm provides direct
         retention.
              Function:- Retention, bracing and stabilization.
The retentive arm of the clasp may approaches the undercut area from the gingival
direction and called bar type clasp. It provides retention only for the partial denture


4-A Reciprocal arm (guiding arm) is a rigid, half round, arm located occlusal to the
          survey line on a surface of the tooth opposing the retentive arm.
  Its main function is to counteracts stresses generated by the retentive arm as it
          crosses the height of contour during insertion and removal of the denture,
          causing lingual (or buccal) movement of the abutment tooth.
                 In order to reciprocate forces properly, it should remain in contact
           with the tooth during function of the retentive arm. Rigid major connectors,
           or minor connectors contacting lingual surfaces of the teeth substitute
           reciprocal arm.
          - Reciprocal arm also stabilizes the denture against lateral movements.
One arm clasp may be used to encircle the tooth. The rigid part of the arm starts on
one side of the tooth and cross-proximal surface to reach the other side of the tooth as
a tapered (retentive) end.

Basic Principles of a Properly Designed Clasp:
        The function of a properly designed clasp is contributed to the following basic
  principles:
   1. Encirclement: The clasp must encircle more than half of the circumference of
           the tooth either through continuous or interrupted contact. This is to
           preclude movement of the tooth and to prevent the clasp from slipping off
           the tooth when stresses are applied.
     2. Support of partial dentures: It is the property of the clasp that enables it to

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           resist displacement in a gingival direction. The occlusal (lingual or
           incisal) rest is the prime support unit of the clasp.
   3. Bracing of partial dentures: It is the resistance against horizontal
         displacement of the prosthesis. This is achieved by the rigid parts of the
         clasp.
 4. Stabilization of partial dentures: It is the resistance against Rotational forces
          acting on the partial denture either in vertical or horizontal direction
          causing rotation (torque) of the denture base around an axis.
 5. Reciprocation: It is the counteraction of the effect of the retentive clasp arm
        on the abutment tooth during insertion and removal of the prosthesis. It is
        provided by the non-retentive clasp arm. .
 6. Clasp arms should be placed at the lower part of the middle third of the axial
        tooth surfaces. While the retentive terminal should be placed at the
        gingival third below the survey line.
 7. Minor connector (or proximal plate) must contact a definite guiding plane to
           dictate path of insertion.
 8. Passivity: the retentive clasp arm should be passive and should not exert any
            pressure against the tooth until a dislodging force is applied.
 9. The clasp should be designed on biologic as well as mechanical bases.
     a- Whenever possible Minimum area contact between clasp and tooth surface
        is provided to minimize food stagnation and incidence of carious lesions.
     b- The clasp should not interfere with normal gingival stimulation and its
        terminal should be away from the gingival margin.
     c- The clasp should be smooth on both its inner and outer surfaces.
     d- Clasp retainers indicated in cases of free end saddles must possess a stress
        breaking action to minimize excessive force on the abutment.
10. Retention: Retention is the basic function of a clasp. The retentive tip of clasp
 arm enables the clasp to resist dislodgment from the tooth in an occlusal direction.
        a- Tip of retentive clasp arm is the only part of the clasp that is flexible
           and located in an undercut.
        b- Amount of retention should be the minimum necessary to resist
           reasonable dislodging force.
        c- Retentive clasps should be bilaterally opposed (balanced retention), i.e.
           buccal retention on one side of the arch is preferably opposed by buccal

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             retention on the opposite side to be effective in retaining the denture.
          d- The path of removal of the clasp terminal must not be parallel to the
             path of removal of the denture.


Factors Determining the Retentive Force of a Clasp:

        Retentive force of a clasp depends on the undercut engaged, flexibility of the
  clasp arm, and angle of approach of clasp arm with the tooth surface.


1- Depth of undercut used
           The greater the depth of undercut present on the abutment tooth the more
       will be the retention generated by the clasp engaging this undercut. The
      retentive undercut has three dimensions. It is measured by undercut gauges
      0.01, 0.02, 0.03 of an inch.
The retentive undercut have three dimensions:-
   1- Buccolingual depth:- It may be measured by undercut gauge. Most clasps
       made of cast chrome alloy are placed in undercuts of 0.010inch. Cast gold clasp
       engage 0.015 inch. While the wrought wire clasps engage 0.020 inch undercuts.
   2- Distance between survey line and the tip of retentive clasp:- It is affected the
       clasp arm length, which influence the flexibility of the clasp.
   3- Mesiodistal length of the clasp below the height of contour :- The longer of this
       measurement, the more flexibility of the clasp.

2-Angle of approach.
            Occlusally approaching clasps are easier in occlusal displacement than
     gingivally approaching clasps. Occlusally approaching clasps are pulled up to
     move occlusally. Gingivally approaching clasps are pushed up to move
     occlusally (Trip action, push or crip action)
            Not all gingivally approaching clasps exhibit trip action for example T or
     modified T clasp may approach under cut from occlusal direction.

     2- The Amount Of Clasp Arm Extends Below The Height Of Contour
 The retentive clasp terminal is placed below the height of contour of an abutment.
The greater distance of the retentive clasp terminal, give greater retentive action.
 3- Angle of gingival convergence (distance to height of contour)

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             The angle formed between the analyzing rod and tooth surface apical to
      the height of contour.
             A two clasps may engage the same depth of undercut but the distance to
      the height of contour varies.
             Less gingival convergence (i.e. the retentive tip is at long distance from
      height of contour) leading to less resistance to vertical dislodging force .
4- Position of clasps in relation to fulcrum axis
   Direct retainer hould be as far away from the          fulcrum axis for mechanical
   advantages

6- Flexibility of clasp arm:
         The more flexible the clasp arm, the less will be the retention. In tooth
      supported partial dentures, more rigid clasps can be used compared to tooth-
      tissue supported dentures.

          By increase the flexibility of the clasp. The magnitude of horizontal stresses
      against an abutment tooth can be reduced.

           More increase the flexibility should not be occurring, because this leads to
      decrease the clasp ability to provide retention.

          The degree of Flexibility possessed by the clasp arm depends on the
      following factors:
  a) The length of the clasp arm:
                    The length of the clasp measured from the point at which uniform
             taper begains .The greater the length, the greater will be the flexibility of
             the clasp arm.
             The length of retentive arm should be at least 15 mm , 7mm in cast and
             wrought wire clasp respectively

             D= Ewt3!! 4PL3

             D= deflection         E= elastic modulus w= width         t= thickness      p=
             applied force l= length

  b) The diameter of the retentive arm:
                    The smaller the diameter, the greater will be its flexibility, all
             other factors being equal. The flexibility is increased by a factor of eight.
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                           The thickness of the tip of the clasp should be half the thickness at
                    the origin.
   c) The tapering:
               The clasp arm should be uniformly tapered in such away that the diameter
               at its origin is twice that at its tip (Fig. 3-121).
   d) The cross sectional form:
                    A round clasp arm is more resilient than half round or oval cross
               section; that are difficult to flex in certain directions.
                 The round clasp is the only universally flexible clasp. Practically it is
               impossible to obtain this universally flexibility by casting & polishing.
               Therefore all cast clasps are half rounds in form.
                      In the half round, the flexibility is limited only one direction. It
               flexible only in tooth ward direction, but the flexibility in the edge wise
               direction is limited. Also the adjustment of this clasp is in the tooth ward
               direction only. The edge wise direction means moving the clasp cervically
               or occlusally.
   e) The material of alloy:
             Gold alloys are more flexible than cobalt chrome alloys.
          The chrome alloys have higher modular of elasticity than the gold alloys,
therefore it is less flexible.
 The modular of elasticity defined as the constant of proportionality between stress &
strain. It is represents the slope of the elastic portion of stress strain curve.
                                   STRESS
ξ = elastic modulus =                      
STRAIN

   f) The type of alloy:
          The wrought form is more resilient than the same alloy of identical diameter
         in cast form, because of its internal structure




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                        Location of the Retentive Terminal
            The retentive terminal is normally positioned at mesiofacial or
    distofacial line angle. The facial or buccal position is preferred over the use of
    the lingual surface as it permits increased length of retentive armand improve
    flexibility.
 1- Placement of retentive arm on the lingual surface of premolar is contraindicated
    .most premolars has limited mesiodistal dimensions so the lingaual retentive arm
    is short and inflexible. The mandibular premolars have a decided lingual axial
    inclination, and as a result the height of contour is located near the occlusal
    surface. Therefore, if lingual retentive area is selected, the clasp would have
    insufficient length provide the flexibility needed.
 2- The maxillary premolars have buccal inclination; this lead to the retention from
    the lingual surface cannot be considered.
 3- In the molar teeth the undercut exhibit on either or both the buccal & lingual
    surface. Therefore, either buccal or lingual retention may be used, depending on
    the most desirable undercut. Particularly mandibular molar which have
    increased mesiodistal dimension and lingual under cut
General Roles in the Location of the Retentive terminals:-
If buccal retention is selected for used on one side of the arch, it should be opposed
    by buccal retention on the opposite side of the arch. Also if the lingual retention
    is selected for used on one side of the arch, it should be opposed by lingual
    retention on the opposite side of the arch.
 If two retentive clasp are to be used on each side of the arch, it is possible to have
    one clasp on each side engage a buccal under cut
When unilateral distal extension ridge is being treated, one clasp on the dentulous
    side, usually on the molar. The other two clasps, usually on the premolars or
    canine on the opposing side of the arch will engage the buccal undercut.


How many clasps for a denture

            Clasps could be located at each end of the denture , this clasping is not
        biologically accepted due to more tooth coverage


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             Instead , two clasps can be used in away that a straight line joining them
         bisect the denture
             If the denture tend to rock about the line joining two clasps , a third
         clasp is added as far as possible from others .

Factors affecting the selection of clasp

         1-   Type of survey line
         2-   Amount and position of under cut
         3-   Position of tooth in arch
         4-   Occlusion
         5-   Appearance
         6-   Amount of retention needed
         7-   Type of denture support and load distribution.
         8-   Anatomic limitations.

  The advantages of any particular clasp design should lie in an affirmative answer to
most (or all) of the following questions:
 1. Is it flexible enough to satisfy the purpose for which it is being used? (On an
   abutment adjacent to a distal extension base, will tipping and torque be avoided?)
 2. Will adequate stabilization be provided to resist horizontal and rotational
 movements?
 3. Will rigidity be provided where it is needed?
 4. Is the clasp design applicable to malposed or rotated abutment teeth?
 5. Can it be used despite the presence of tissue undercuts?
 6. Can the clasp terminal be adjusted to increase or decrease retention?
 7. Does the clasp arm cover a minimum of tooth surface?
 8. Will the clasp arm be as inconspicuous as possible?
 9. Will the width of the occlusal table remain the same or be decreased?
 10. Is the clasp arm likely to become distorted or broken? If so, can it be replaced?


The essential function of clasp are :

   1-Retention: by the flexible part of the arm.
   2- Support: by occlusal rest.
   3- Bracing: by the rigid part of the arm.


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       Cone theory
       In 1916 protherio present a cone theory to explain clasp retention , he described
       the crown form as two cones sharing common base.
       De van ‘s concept
       De van divided the abutment into suprabulge and infrabulge portions



                              Types of Clasp Retainers

Clasp Classified On basis of design into:


I- Occlusal1y Approaching clasps (Circumferential clasp) class Π

I- Gingivally approaching clasp (Bar-type clasp, infrabulge or roach) class I
II-Combination

Clasps can be classified according to the material used into:
  1.        Cast clasps
  2.        Wrought wire clasps.
  3.        Combination cast and wrought wire clasp.

  Clasp Classified On basis of movement accommodation

       - Clasps accommodate functional movement

       Bar clasp                                       RPI
       Combination clasp                               RPA
       - Clasps without movement accommodatation
        Multiple clasp                                  Circumferential clasp
        Half and half clasp                             Ring
        Reverse action                                  Embrasure clasp
        -                                               Back action




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Clasp Classified On basis of design into:


I- Occlusal1y Approaching clasps (Circumferential clasp)
              The retentive terminal approaches the undercut of the tooth from above
        the survey line, the retentive arm originates at the minor connector usually
        near the occlusal rest. e.g. Akers, back action, reverse back action, ring clasps.


II- Gingivally approaching clasp (Bar-type clasp, infrabulge or roach):
         The retentive terminal originates from the denture base buccal to the
         edentulous ridge, crosses the free gingival margin to approaches the retentive
         undercut from below the survey line. The tip of the retentive arm may be in
         the form I• T, U• C or Y.


I- Occlusally Approaching Clasps.
Called encircling, circumferential, or suprabulge clasps.

Definition: it is a retainer that encircles a tooth by more than 180 degrees, including
opposite angle, and which generally contacts the tooth throughout the extent of the
clasp, with at least one terminal located in an undercut area.
 Component parts of the clasp assembly:-
1- Rest:          location: - it is lie on the occlusal or lingual surface or
                on the incisal edge.
            Function: provide support for RPD.
2- Body         Location: - above the height of contour.
             Function: - connect the rest and clasp arms to the minor
             connector.
3- Reciprocal arm           Location: - above the height of contour on the side
                          of the tooth opposing the retentive clasp arm.
                    Function: - 1- Resist the tipping force generated by
                                retentive terminal.
                             2- Help in stabilization of RPD against
                                lateral movements.
                            3- Support the prosthesis due to it lie on
                               the supra bulge.

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 The reciprocal clasp arm must be contact to the tooth before retentive clasp arm pass
over high of contour, and remain in contact while the retentive terminal passes the
height of contour, to resist the tipping force.
4- Retentive arm: - it includes two parts:-
    A) Shoulder              Location:- above the height of contour (NOT
                        FLEXABLE)
                           Function:- connect the body of the clasp terminal.
   B) Retentive terminal             Location: - below the height of
                                    contour (FLEXABLE).
                                    Function:- provide direct retention.
5- Minor connector:-        It is the part of clasp that joints the body of the clasp to the
remainder of the framework ( IT MUST BE REGIDE).




                           CAST CIRCUMFERENTIAL CLASP
  RULES FOR USE
       The retentive clasp arm should originate above the height of contour &
terminated below it. While, the retentive terminal should be pointed toward the
occlusal surface, never toward the gingiva.
       These produce a curved clasp which increase the length of the arm as well as
increase the flexibility. The retentive tip should be terminating at the mesial or distal
line angle of the abutment tooth.


Problems of cast circumferential clasp:-
   1- Obtaining Sufficient Occlusal Clearance: - if the opposing occlusion is tight, it
       is often difficult to obtain adequate clearance to place the rests & clasp without
       removing a prohibitive amount of tooth structure on the abutment & it is
       antagonist teeth.
   2- Protection of The Marginal Gingiva Adjacent to The Abutment tooth:- when
       the occlusal rest is placed on the surface of the tooth away from the edentulous
       space, this does not protect the marginal gingiva adjacent to the abutment
       tooth. This marginal gingiva may be traumatized if food pecks between the
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      denture & the proximal surface of the tooth. Therefore advisable to place an
      additional occlusal rest next to the edentulous space to eliminated this problem.
      But this additional rest will decrease or eliminate the releasing action of the
      clasp tip as the denture base is depressed on the distal extension side.
   3- Poor esthetic result with excessive display of metal.


                          1- Aker’s clasp simple circlet clasp
 It is most often the clasp of choice on tooth support RPD this clasp usually
approaches the undercut on the abutment tooth from the edentulous area.
      Engages an undercut of 0.01inch (1/4 mm) on the buccal (or lingual) surface of
molars or premolars far from the edentulous area

Indications:
      a. Acker clasp is considered best suited for strong abutments teeth because it
         transmits the force directly to the tooth and reduce stress on the residual
          ridge.
      b. It is, therefore more often used in unilateral and bilateral tooth borne
         partial denture.
Advantages of Aker clasp
      1-This clasp fulfills the requirements of support, stability, encirclement,
      reciprocation, and passivity better than any other types of clasp.
      2- It is easy to construct and simple in repair.

      3 - Does not distort easily.
Disadvantages of Aker clasp
               a. More tooth surface is covered than with bar clasps. This may cause
                   enamel decalcification or caries.
               b. The Aker clasp changes the morphology of the abutment crown. This
                  may interfere with the normal food flow pattern and with the
                  physiologic stimulation of the gingival tissues.
               c. Due to its half round cross-section, the Aker clasp can be adjusted to
                  the tooth surface in an inward or outward (Bucco-lingual) and not
                  upward or downward (occluso-gingival) direction. This mode of
                   adjustment may only increase or decrease friction on the tooth

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                  surface but does not change the retentive qualities arising due to
                  engagement of an undercut.
               d. The clasp cannot be used in free-end saddle cases due to its rigidity,
                  except with a stress equalizing design.


Cotra-indications: Free end saddle cases (Kennedy class I and II).
           Other forms are modifications of the circlet to suit the location of
     retentive undercut, position of the abutment, or to modify the flexibility of the
     clasp arm.


Modifications of the Aker's clasp

A- The reverse circumferential clasp: reverse approach
              It is a cast circumferential clasp consists of:
          1.      Occlusal rest located away from the edentulous area.
          2.      Retentive arm that engages an undercut near the edentulous area
             (near zone).
          3.      A rigid reciprocal arm.
  Indication:
      It can be used in distal extension cases when the bar clasp is contraindicated
          (when?).
      The effect on the abutment tooth is reversed from that of the conventional
          circumferential clasp.
   Advantage:
      As when occlusal load is applied to the denture base, the retentive terminal
          moves further gingivally into the undercut area and loses contact with the
          abutment tooth (disengagement). In this manner torque is not transmitted to
          the abutment tooth.
   Disadvantage:
               The reverse circlet clasp, because it normally projects between two
         teeth, may produce some wedging force. This can usually be countered by
         occlusal rests on the approximating surfaces of both teeth.




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B- The Multiple Aker Clasp (Multiple circlet clasp)

         The multiple Aker clasp consists of two opposing Aker’s clasps, Two
      Lingual rigid reciprocal arms are connected together at the terminal ends to
      augment their rigidity.


Indications:
   The multiple Aker clasp is used

       Splinting of periodontally affected teeth is needed.

       Multiple clasping is needed in instances in which the partial denture replaces
        an entire side of the dental arch.

       Available retentive areas are only adjacent to each other.
 disadvantage : utilizing two embrasures rather than a common one.


C- The Hair-pin Clasp (C- Clasp – Fishhook)

           It is a circlet clasp with its retentive arm turned back (curved ) to engage
      an undercut near the edentulous area (below the point of origin).


    Indication
    1- when the retentive clasp must engage an undercut adjacent to the occlusal rest
         or edentulous space and a soft tissue undercut precludes the use of a bar
         clasp.

   2- When the reverse circlet clasp cannot be used because of lack of occlusal space.
   3- when a proximal undercut must be used on a posterior abutment and when
      tissue undercuts or high tissue attachments prevent the use of bar type clasp.
    Its disadvantages are:
        1. greater coverage of tooth surface, that increase the functional load on the
           abutment.
        2. food trapping at the loop of the arm, and
        3. inferior esthetics.


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D- The half and half clasp (Split cast assembly):

           It consists of a circumferential retentive arm arising from one side of the
     tooth and a reciprocal arm arising from the other direction on the opposite side
     of the tooth. Since the second arm must arise from a second minor connector,
     therefore an auxiliary rest may sometimes be used.
             It is used with isolated premolars and molars for bounded and free end
     partial denture.
              This clasp was designed originally to provide dual retention, and it should
     be apply only unilateral denture designed.


E- The Extended-arm Clasp

              The extended arm clasp has the same form as an Aker clasp but its arms
       are extended to cover the abutment tooth and the tooth adjacent to it. The
       bracing arm lies above the survey line of both teeth. The retentive arm also lies
       above the survey line of both teeth and then tapers to engage the undercut of
       the second tooth. It is more liable to distortion if its thickness is incorrect.

             If this clasp is made in gold alloy the uses is restricted to the premolars,
       but with chrome cobalt alloy along arm can be used and two molars can be
       clasped.

Indication:
          The clasp is used when the undercut on the tooth near the edentulous area
     is poor, while that on the adjacent tooth is suitable.



Advantages of extended arm clasp
        a. The clasp has splinting action.
        b. Distributes the lateral load over the two teeth.


F- The Double Aker Clasp

       The double Acker clasp is also called embrasure clasp, Compound clasp,
Butterfly , modified crib clasp, Bonwill clasp or Interdental clasp.



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   It consists of two Acker clasps arising from a common body and from the same
minor connector, which is located in the embrasure between the two clasped teeth.
   Indication
          1- on the dentulous side of unilateral edentulous cases (Kennedy class II or
             III having no modifications).
           2- Kennedy class IV (on the posterior teeth).
    It is used primarily to provide bilateral stabilization, and bracing, in addition to
retention. It also splints the two teeth


   The retentive arms of embrasure clasps are always of
the supra bulge type. Although double or single infra
bulge clasps have been used, they tend to create food
repositories and are therefore not the retainers of choice
except in rare cases.


   g- Anterior circumferential clasp




                            2- RPA clasp (RPC clasp)

                  Mesial Rest, Proximal plate and Aker arm ,
                                 (circumferential Clasp).
       The clasp is formed of:
   A mesial occlusal rest arising from a minor connector located in the mesiolingual
         embrasure,
   A proximal plate placed on the occlusal third of the distal surface of the abutment
         and properly extended towards the distolingual line angle of the tooth, in
         contact with a prepared guiding plane, and




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        An Aker circumferential retentive arm arising from the superior portion of the
             proximal plate. and extends around the tooth; tapered to engage the mesio-
             buccal undercut.
                       The rigid bracing portion of the arm should contact tooth only along
               superior border of the survey line. When an occlusal load is applied to the
               denture base, the retentive arm can move into the undercut because of the
               relief under its rigid section and release from the abutment tooth.


                 If a conventional Akers clasp is used, with the retentive arm coming off
          the proximal plate above the survey line and crossing the survey line in the
          middle of the tooth to engage the undercut then the vital releasing capability will
          be lost.


        Indication:
                    It is indicated in distal extension RPDs presented with shallow
             vestibule or severe tissue undercut that contraindicate the use of the gingivally
             approaching clasps.
        Advantages:
1.         The RPA assembly is designed with the rest on the mesio-occlusal surface of
     the tooth, permitting the other components to release from the tooth and drop into
     undercuts when occlusal loads are placed on the denture base. This in turn prevents
     tipping of the abutment.
2.         Absence of a lingual rigid reciprocal arm minimizes rotational forces falling
     on the abutment.


                                         3- RLS Clasp
                  (Mesial Rest, L-bar direct retainer and Stabilizer)
                  It is a lingually retained clasp assembly for distal extension removable
          partial dentures. This clasp assembly fulfills the biomechanical principles and
          the esthetic requirements of patients.




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The RLS clasp assembly consists of:


  1) A mesioocclusal rest.
  2) A distolingual L-bar direct retainer,
        located on the distal surface of
         the abutment tooth. Engages the
         distolingual undercut adjacent to
         the edentulous ridge.


  3) The distobuccal stabilizer (proximal plate): Reciprocate the horizontal force,
      transmitted to the tooth by the activated retentive tip of the direct retainer, The
      distobuccal stabilizer emerges from the framework distobuccally and ascends
      to the height of contour, then it diverges distally and/or lingually to complete
      the encirclement of the tooth.
      Cross-arch stabilization is provided by the minor connectors located
       lingually, and the L-stabilizers located buccally


Advantages:
  1. The mesio-occlusal rest reduces the anterior component of movement of the
     denture and reduces torque on the abutment tooth.
  2. A retentive clasp tip placed on the most distal part of the tooth will undergo a
     downward vertical movement and disengage as the distal extension base
     moves tissue-ward in function.



                            4- Back Action Clasp

  The back action clasp is a single arm clasp, provide single bracing only .

  The minor connector originates from the major connector. It starts at the of
      mesiolingual line angle.

  The bracing arm extends above the survey line on the palatal surface till the
      proximal surface, then starts its taper to engage a mesiobuccal undercut of
       0.01 of an inch.




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   The occlusal rest is located distally,and some times an additional rest could be
       employed on the mesial side to improve support.



Indications:

         (1)   The back action clasp is usually used on
      maxillary premolars and molars. Because of the
      natural tendency of upper teeth to incline buccally,
      they usually have undercuts on the buccal side.

       (2)     The clasp is sometimes used in posterior free-end
     saddle cases due to its flexibility and stress breaking action.
Disadvantages of back action clasp
The back action clasp is both biologically and mechanically unsound. it has the
following disadvantages:
   1. Excessive tooth coverage.
   2. Easily distorted because of length and difficult to adjust.
   3. Excessive display of metal, hence it is esthetically unsatisfactory.
   4. The occlusal rest is supported by the clasp arm and not by a rigid minor
      connector, hence the rest cannot function adequately.
   5. The clasp provides poor bracing and reciprocation.so it is contraindicated in
      unilateral partial denture
   6. Food is trapped between the palatal arm and the major connector due to
      insufficient space (clearance) between them.



                        5- Reverse back action clasp

           The Reverse back action is similar in structure to the back action but it is
    located in the reverse direction.
           The minor connectors originates buccally from the saddle starts at the
    mesiobuccal line angle and ends to engage a mesiolingual undercut of 0.01 or
    0.02 of an inch.
         The clasp is Frequently used on lingually tipped bicuspids. It also provides
    single bracing only. It has an additional esthetic disadvantage.

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                                       6- Ring Clasp
   The ring clasp is a single-arm clasp, indicated on tilted, isolated molars.
   It originates mesially and the single arm encircles nearly all the tooth surface
          resembling a ring.
   It is generally exhibiting a mesiobuccal undercut in case of upper molars and a
         mesiolingual undercut on lingually tilted lower molars. The clasp engages a
         0.02 or 0.03 of an inch undercut.
   The occlusal rest is located on the mesial marginal ridge.

   An auxiliary distal rest is preferably added to prevent further mesial tilting of the
       tooth.
   A reinforcing supporting strut arm located on the non-retentive side is usually
          considered to limit the flexibility of the clasp.

Disadvantages of ring clasp:
   (1) Excessive tooth coverage that may result in enamel
  decalcification and caries.
    (2)   Easily distorted because of length and difficult to adjust.
   (3) Reinforcing arm may cause marginal irritation and inflammation and
  may act as a food trap.

                                    7- Onlay Clasp


It is an extended occlusal rest with buccal and lingual clasp arms. The clasp may
originate from any point on the onlay that will not create occlusal interferences.
Indications:
1- when the occlusal surface of the abutment tooth is below the occlusal plane.
  If the onlay clasp is constructed of chrome alloy and is opposed by a natural tooth,
the occlusal surface should be constructed of acrylic resin or gold.



II- Gingivally Approaching Clasps




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      These clasps are also called Infra-bulge, I-Bar, Vertical Projection or Roach
clasps.

      The bar clasps approach the undercut or retentive area on the tooth from a
gingival-direction, resulting in a "push" type of retention. This push retention of bar
clasps is more effective than the "pull" retention characteristic of circum.
Disadvantages of bar clasps:-
     1- Greater tendency to collect and hold food debris.
     2- The increased flexibility of the retentive arm, it does not contribute as much
     to bracing and stabilization. Additional stabilizing units.


 The flexibility of the bar clasp can be controlled by the taper and length of the
approach arm.


Contraindication:

It is contraindicated if the undercut is more than 1mm or the depth of the buccal sulcus
is less than 4mm.




Component parts of clasp
1- Approach arm : It is a minor connector that joins body and retentive terminal of
clasp to framework.
2- Retentive clasp arm and retentive terminal: It must be flexible and located gingival
to the survey line.
3- Reciprocal clasp arm is usually in the form of a circumferential clasp arm and
rarely in the form of bar arm
4- Occlusal rest

Indications:
    -It is used mainly in unilateral and bilateral free end cases to minimize the
      torque on the abutments.
    -It provides better retention and better esthetic but less bracing than Aker's
    -It can utilize different amount of undercut.


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Contra-indications:
    - Deep cervical undercut on abutment or excessive tissues undercut. To avoid
        food impaction.
    - Shallow sulcus.


RULES FOR USE:-

   1- The approach arm of the bar clasp must not impinge on the soft tissues it is
       crosses. It is not desirable to provide an area of relief under the arm, but the
       tissue side of the approach arm should be smooth& polished.

   2- The approach arm should cross the gingival margin at a 90-degree angle.

   3- The approach arm must extend on the abutment tooth to the height of contour.
       The retentive terminal leaves the approach arm at that point and extends into
       the undercut area. The tip of the retentive terminal must be end toward the
       occlusal surface. (The approach arm contacts the tooth only at the height of
       contour).

   4- The bar clasp should also be placed as low on the tooth as possible while
       honoring the height of contour to reduce the leverage-induced stress to the
       abutment tooth.

   5- Functional depth of vestibule at least 5mm.

   6- Superior border away from gingival margin by at least 3mm.

   7- The approach arm must be tapered uniformly from it is attachment to the clasp
       terminal. It must never be designed to bridge soft tissue a undercut, to avoid the
       tapering of food & to avoid the irritation of cheeks or lips.

   8- The approach arm should taper gradually and uniformly from its origin to the
       retentive end.

   9- It must not bridge a soft tissue undercut to avoid food trapping and irritation .




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10- The tip of the retentive arm may be in the form of I.T.U.C or Y . One end of
   the T or Y engage undercut while the other end placed above the survey line
   the only function of this additional end is to encircle more than 180º of the
   tooth, if the retentive undercut is near to minor connector and occlusal rest.

11- The bar--type clasp is said to have a "push" type of retention (Trip action of
   the clasp). As this arm is relatively longer than occlusally approaching arm, it
   is considered as a more flexible arm. However, curvature of the arm in more
   than one plane minimizes this expected high flexibility.

12- Tripping action is attributed to clasp arms that engage the undercut directly
   from a gingival direction. Not all bar clasp arms have tripping action, since
   the retentive terminal may actually engage the undercut from an occlusal
   direction as is true with the "T" bar or modified "T" bar




Types of Bar Clasps

               1- The I-bar clasp (Roach clasp arm)

 The I- bar clasp consists of:

 A retentive clasp arm originating from the denture base• approaching the buccal

      undercut from a gingival direction. It provides retention only.

  A rigid reciprocal clasp arm on the opposite side of the tooth. This arm is
      usually in the form of a circumferential clasp arm and rarely in the form of a
      bar arm. This arm is located above the survey line. It provides bracing and
      reciprocation.

  An occlusal rest and a minor connector joining the rest with the framework.

    It is used on the distobuccal surface of maxillary canines for esthetic reasons.
      There is a definite danger involved in using this clasp. Because the only
      contact of the retentive clasp with the abutment tooth is the tip of the clasp,
      an area of 2-3 mm, encirclement and horizontal stabilization may be
      compromised.


a- T Clasp
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     The T clasp is used most often in combination with a cast circumferential
reciprocals arm.
Indications of T clasp:-
      1- The T clasp is used most frequently on a distal extension ridge where the
           usual undercut is on the distobuccal surface of the abutment tooth. When
           tissue ward forces occur on the denture base, the terminal clasp tip rotates
           cervically into a greater undercut, this reduces the torquing stresses to the
           abutment tooth.


      2- In class I or II R P D where the retentive undercut on the distobuccal surface
      of the abutment. This retention can best be secured by T clasp.
      3- The T clasp can also be used for a tooth-supported partial                denture
           when the retentive undercut is located on the abutment tooth adjacent to the
           edentulous space.
Contraindications:-
   1- The T clasp should not be used on a terminal abutment adjacent to distal
       extension base if the usable undercut is located on a fare zone of the abutment
       tooth.
   2- Also, this clasp can never be used if the approach arm must bridge a soft tissue
       undercut.
   3- T clasp should be avoided if height of contour of abutment tooth lies close to
       occlusal surface. Because a large space would be created between approach
       arm of clasp and tooth. Space would trap food. High position would also be
       unaesthetic.


   b- Modified T Clasp
The modified T clasp is essentially a T clasp with the nonretentive finger (usually
mesial).

   This clasp is most often used on canines or premolars for esthetic reasons.
The potential danger in its use is that encirclement, or 180-degree coverage, of the
abutment tooth may be sacrificed to esthetics.


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         Esthetics should always be considered when the partial denture is being designed,
     but its consideration must not supersede the necessity of making the prosthesis
     mechanically acceptable. An esthetically superior denture that leads to ultimate
     destruction of the remaining oral tissues is not in the best interests of the patient.


     c- Y Clasp
  The Y clasp is basically a T clasp; it's used when the height of contour on the facial
 surface of the abutment tooth is high on the mesial and distal line angles but low on
 the center of the facial surface.

          On occasion, careful recontouring of the enamel surface of the abutment tooth
 will permit the Y clasp to be converted to the standard T clasp.
    d- L clasp
  It is a modified T clasp.
    e-     U clasp
There are two bars effectively engage the undercut, retention will be improved.



                       2- The RPI clasp (Kratochvill’s system)

                              (Rest, Proximal Plate and I Bar)


      The RPI clasp is a current concept for bar clasp design, as the full “T” bar should
 not be used since it covers an unnecessary amount of tooth structures compared with
 the RPI clasp.


  Basically the clasp assembly consists of:


   1- A mesio-occlusal rest:
             A mesio-occlusal rest with the minor connector placed into the
           mesiolingual embrasure.




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2- A proximal plate:
   a- It is placed on a distal guiding plane, extending from the marginal ridge to
      the junction of the middle and gingival third of the abutment tooth.
   b- The proximal plate minor connector should contact approximately 1 mm of
      the gingival portion of the guiding plane in distal extension cases.
   c- The bucco-lingual width of the proximal plate is determined by the proximal
      contour of the tooth.
    - The proximal plate together with the mesiolingually placed minor
      connector provides stabilization and reciprocation of the assembly.
   3- The I bar arm:
      a-       It should be located in the gingival third of the buccal or labial surfaces
           of the abutment in 0.01 of an inch undercut.
      b-       The I-bar approaches the undercut in a vertical direction at the center
           of the abutment tooth.
      c-       It may be placed towards the mesial but not towards the distal to avoid
           torquing of the abutment tooth when a vertical load is applied on the distal
           extension base (.
      d-     The whole arm of the I-bar should be tapered to its terminus, with no
           more than 2 mm of its tip contacting the abutment.
      e-      The base of the I-bar must be located at least 4 mm from the gingival
           margin.
      f-      Slight relief is required where the arms crosses the gingival margin.




 Indications:


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   The RPI clasp is indicated:
      a-      In distal extension cases, as it provides a stress releasing action.
      b-      When tissue undercuts are not severe.


 Contraindications:
   The RPI clasp is contraindicated with:
        a-       Shallow vestibule (the base of the I-bar should be at least 3mm from
        the gingival margin).
        b-        High floor of the mouth which necessitates the use of lingual plate.
        c-        When buccal undercut is absent or only distobuccal undercut exists.
        d-        In cases with severe tissue undercut to avoid food or tissue trap.
        e-      If the facial surfaces of teeth are facial to the tissue surface, the RPA
        clasp may be used.


                                 3- The RII clasp

    This clasp is basically indicated for posterior teeth or a single isolated last
molar. The RII clasp is composed of:
a- Occlusal Rest (R) located on the side of the tooth near the edentulous area.
b- Two I bar arms (II): one arm Located on the lingual or palatal surface of the
    abutment above the survey line, this arm is usually rigid for bracing.
             The other arm is a flexible retentive arm located on the buccal surface of
     the abutment tooth. The retentive terminal uniformly tapered engages an
     undercut of 0.01 of an inch below the survey line (Fig.3-150).
  Support is provided by occlusal rest,
  Bracing is provided by mesial minor connector and rigid lingual I bar.
  Retention is provided by buccal I bar, and
  Reciprocation is provided by mesial minor connector and rigid lingual I bar.


                       4- The Ball and Socket clasp

  It is a bar type clasp, used when the tooth surface having no undercut.


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      The retentive arm is a round platinized gold wire, with a ball at one end.
       This end engages a dimple on the buccal surface of the tooth prepared in a
       gold inlay..



             5 - CLASPS UTILIZING PROXIMAL UNDERCUTS

 a- Infrabulge clasp (the DeVan clasp):

             It is designed so that the Lingual aspect may be open or plated.
             Two occlusal rests on each abutment are used. The bar arm arises from the
      border of the denture base, either as an extension of a cast base (C), or it may be
      in the form of wrought wire clasp attached to the border of a resin base. Wrought
      wire clasp arm could be used if additional flexibility is required (D)
             It has a small head that bears on the tooth interlay below the survey line.
      The De Van clasp should be reciprocated by a lingual or palatal strut which
      contact the tooth at the junction between the lingual or palatal & fare proximal
      surface. This strut end in a lingually or palatally placed occlusal, the primary
      occlusal rest being placed on the near proximal part of occlusal surface. This
      reciprocating arm may be replaced by an embrasure hook.

            The DeVan clasp is highly retentive and esthetically agreeable due to its
      proximal location. But food debris may be entrapped between the arm and the
      denture base.
Advantages of De Van clasp:-
1- It can used when a buccal or lingual survey line are unfavorable.
2- Good esthetics even when used on premolars& canine. Because, it is can be hidden
   behined the buccal convexity of the tooth.
3- Good retention/ due to the angle of approach of the clasp to the undercut which gives
   a marked trip action.
4- It is compact design in relation to the saddle periphery helps to prevent it is
   accidental displacement.




     b- Mesio-distal clasp


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   It may be used when clasping canines. specially when little undercut on the buccal
surface of canine, or to avoid the clasping of the buccal surface which is esthetically
displacing. This clasp is always cast in gold & embraces the canine on the mesial,
palatal & distal sides.

       The mesial surface of the canine should be cut or reduced to create a necessary
space. If a diastema is exists between the canine and lateral incisor this space
provides an accommodation for the mesial part of the clasp without reduction of the
mesial surface of canine.

 In free end saddle cases, it must be employed without using a stress breaker.

Advantages of mesio-distal clasp:

    1 It is accepted esthetically.

     2- Give good retention& grips the tooth rigidly.




               Comparison Between Occlusally and Gingivally
                              Approaching Clasps



            Both occlusally and gingivally approaching clasps are cast clasps
       achieving the same design principles, however, they exhibit the following
       differences:
 1. Retention:
             Gingivally approaching clasp gives better retention than occlusally
       approaching clasps through the trip action of the clasp, as it pushes toward the
       occlusal surface to resist displacement, while the occlusally approaching clasp
       pulls toward the occlusal surface to resist displacement.
 2. Bracing:



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             Since the occlusally approaching clasp arm generally has a rigid portion
      lying in contact with the non-undercut zone of the tooth, its bracing effect is
      greater than the gingivally approaching clasp.
 3. Caries Susceptibility:
             The incidence or caries under clasp arms may said to be inversely
      proportional to the efficiency of the patient's oral hygiene. If cementum is ex-
      posed, there is some risk of cemental caries with gingivally approaching arms.
              While the occlusally approaching clasp covers more of the tooth surface,
      this increases the susceptibility of enamel caries.
 4. Gingival Health:
             When properly designed, clasps are used in combination with adequate
      tooth support of the denture. Gingival health is rarely affected.
            Traumatic gingivitis, however, more often seen with gingivally
       approaching clasps, either as a result of inadequate relief of the clasp arm, or
       through its accidental displacement.


 5. Esthetics:
              The gingivally approaching clasp has sometimes to be preferred
       than the other, due its proximity to gingival margin, hence are less visible.
              However, in cases, where the gum is shown as in the gumy smile
       patients, the gingivally approaching clasp is even more noticeable than
       occlusally approaching clasp.
7-Tolerance:
             The gingivally approaching is less tolerated specially if excessive
       block-out is done leading to food and tissue trap.
8- indication:
             The occlusally approaching clasp is indicated in case of Tooth
       Supported RPD, when esthetic s not important because of its stabilizing
       ability.
             The gingivally approaching is indicated incase of Tooth- Tissue
       Supported RPD, because of its stress releasing action. And in case of Tooth
       Supported RPD when esthetic is the prime concern.

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Classification of Clasps according to the mode of construction and the
material used:
Clasps can be classified according to the material used into:
1 - Cast clasps
2 - Wrought wire clasps.
3 - Combination cast and wrought wire clasp.


1-Cast metal clasp:
                  a.   The cast clasp is either gold or cast chromium alloy.
                  b.   It is half round in cross section.
                  c.   It contacts tooth surface at an area.
                  d.   It flexes in one plane (to or away from tooth surface) only.
       Advantages of cast clasps:
              a.       They exhibit an accurate fit to tooth surface.
              b.     Can easily be varied in thickness, form and taper during their
              construction.


2- Wrought wire clasp
              a. The wrought wire is a buccal retentive arm. Usually made of either
                 0.7 or 0.8 mm round stainless steel, or gold alloy wires embedded
                   in the acrylic base.
              b. This type of clasp is extremely resilient, however, it possesses poor
                 stabilization properties.
              c. It flexes in two planes (to or away from tooth surface and up or
                 down parallel to tooth surface).
              d. It has line contact with tooth surface creating less friction.
              e. Due to its flexibility it can be easily distorted.
              f. Its common use is in acrylic dentures.


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Wrought wire clasps may be in the form of :
1-        Simple circlet clasp
      a. The clasp is either soldered to metal framework or embedded in the acrylic
       resin lining the denture base. The clasp is used on teeth adjacent to the
       edentulous area.
      b. It should pass 3-4 mm away from the proximal surface of the clasped tooth
       to allow for the adjustment of the denture during insertion.


2. Jackson-Crib Clasp (Modified Crozat Clasp)
      a. This is a completely encircling clasp with no free flexible terminal.
      b. It provides retention because those parts of the clasp, which are situated on
       the proximal embrasures of the tooth, are springy and grip the undercuts in
       these areas. It acts as a clasp and occlusal rest.
      c. It is used with acrylic denture and made of 0.7-mm gauge wrought wire.
      d. It indicated on molars and premolars when no edentulous space exists on
       either side of the tooth to be clasped.
      e. It starts at the point of attachment of the base on the lingual side and passes
       up to cross the occlusal surface and then down to the buccal surface along the
       gingival margin and then up again to cross the occlusal of the other contact
       point to gain attachment to the base of the lingual side.
1.        Split crip
When cut at the middle of buccal surface
2.        Half crip
When it does not reach the other embrasure.


Advantages of wrought wire clasps
     a.   Less tooth coverage as the clasp makes a line rather than an area of contact
      with the tooth surface.
     b. Minimum friction.


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                                                                               Direct retainers


     c. The clasp is highly flexible, hence can be used in distal extension bases
      requiring stress breaking action.
     d. Easily constructed.

     Wrought-wire direct retainer arms may be attached to the restoration by
     1- Embedding a portion of the wire in a resin denture base,
     2- By soldering to the fabricated framework, or
     3- By casting the framework to a wire embedded in the wax pattern.


    Wrought-wire retainer arm has been contoured to follow the design and is
incorporated into the wax pattern




3-Combination clasp
       It is essentially a cast clasp in which wrought wire has substituted the
buccal cast retentive arm. If this term is used the term wrought wire clasp is limited
to wrought wire retention arms reciprocated by acrylic or metal lingual or palatal
plates
       If the partial denture framework is to be constructed of gold or low-heat
chrome alloy, the wrought wire clasp can be incorporated into the framework
during the waxing step and the alloy can be cast directly to the wrought wire clasp.
If a high-heat chrome alloy is used, the wrought wire must be soldered to the
completed framework.
Indication:
- on an abutment tooth adjacent to a distal extension space when the usable
undercut on the tooth is on the mesiobuccal surface.
Advantages of the combination clasp
1-       Combines both the resiliency and flexibility of the wrought retentive arm
and stabilizing effect of the cast clasp.
                The clasp has a stress breaking action. The wrought wire acts as a
         stress equalizer preventing the undesirable forces created by the lever action
         of the retentive clasp tip from lifting or torquing the abutment tooth as
         downward forces occur on the denture base.



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             The greater flexibility of this clasp allows it to place in a greater or
       deeper undercut.
2- Adjustability:-
        The round wrought wire clasp can flex in all spatial planes, which allow it
to dissipate torquing forces exerted on the abutment tooth & to be adjusted in all
planes.
3- appearance:-
       The wrought wire clasp may be used in small diameters than the cast clasp.
Since it is round, light is reflected in such a manner that the display of metal is less
noticeable than with the border surface of the cast clasp.
4- Caries less:-
The round wire makes only a line contact with the surface of the abutment tooth.
This minimal contact of makes it is used in caries- prone mouths some what may
beneficial.
Disadvantages of combination clasp:-
1-     It does require extra steps in laboratory fabrication.
2-     It is also more prone to breakage or damage than a cast clasp.
3-    It can be easily distorted by careless handling by patients, who tend to
remove the partial denture from the mouth by lifting on the retentive portion of the
wrought wire clasp.
     Because of the increased flexibility of the retentive arm, it does not possess
the bracing or stabilizing qualities of most circumferential clasps. If stabilization of
the teeth or of the partial denture against horizontal forces is needed, the
combination clasp would not be a good choice.
     These disadvantages should not prevent the use of this clasp regardless of the
type of alloy being used for cast frame work. The technical problems are
minimized by selecting the beast wrought wire for this purpose.
The patient may be taught to avoid distortion of the wrought wire by explaining
that the fingernail should always be applied to it is point origin, where it held rigid
by casting.




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                                                                    Direct retainers




                       OTHER TYPES OF RETAINERS


                     Grasso’s clasp (VRHR clasp concept)
The VRHR clasp assembly consists of:-
1-     Distal occlusal rest supported by minor connector.
2-     Lingual Vertical Reciprocal arm originated from major connector.
3-    Horizontal Retentive arm fixed either to the major connector or to the
framework.
Each arising separately fram the denture base.
        This clasp design is especially useful on mandibular molars and premolars
that have heights of contour in the occlusal third of the crown.
        The reciprocal component of this clasp designed to contact the lingual
height of contour at the greatest mesiodistal prominence.
     The horizontal retentive arm is generally parallel to the occlusal plane&
placed completely below the height of contour with only the terminal third of the
clasp contacting the abutment tooth; the remaining two third is positioned slightly
out of contact with the tooth surface. The degree of the space between a rigid part
of the retentive clasp & the tooth surface is determined by the amount of the
undercut that usually fracture of mm.
  Advantages of VRHR clasp:-
1-     Make a minimal contact with the teeth.
2-     Providing continuous contact during insertion and removal of the
prosthesis.
3-     No need to developed lingual ledges.

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4-    Suitable for posterior teeth with high survey line .
5-    Placement of retentive arm is more esthetic
6-    Doesnot require preparation f guide line .
7-    The balance between the retentive arm and the reciprocal component
prevent the whiplash effect of the retentive arm.

                         NavasCampo (NC) clasp

      It is suggested by Navas & Campo. It is a special design for a tissue -
supported, distal extension RPD for patients who require a combined fixed
removable prosthesis and this system provides to overcome the esthetic problem,
retention, bracing, and support for distal extension base RPD with minimal damage
to the abutment teeth and the supporting tissues. This clasp is intended to minimize
loads on the abutment teeth during functions:


The “NC” design consists of:
-     The minor connector: connects a ball - shaped pin to the major connector,
and helps guide the RPD into place. It has no retentive properties and is free to
slide up and to down the prepared slot, acting as stabilizer. There are no vertical
stops on hard tissue because this is a soft tissue supported type of prostheses.
-      An active arm in close contact with the abutment tooth separates from it
under the forces of mastication, with the denture base forming a hollow space that
protects the marginal gingiva.
-     The retention is gained through a ball pin, which fit into machined grooves
in fixed partial denture. The ball shaped pin, serves as the guide for insertion and
removal of the prosthesis, it is made to rest midway along the superior and inferior
limits of the grooves.
-     Under the pressure of mastication, the NC clap is deactivated and the balls
can move downward along the transverse axis with a slightly rotational movement.
-     When the mouth is opened, the NC clasp is activated and the balls move
upward along the transverse axis with a slightly rotational movement.
-      The esthetic problem is solved because no metal is visible on the facial
surface of the arches. The size of the ball and gauged groove is shown in.



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    Retention is provided by the anatomical alveolar ridges and muscles and by
mechanical factors such as the NC clasp, which keeps the prosthesis joined to the
abutment tooth. Bracing is provided by the ball inside the groove, the well fitting
denture bases, and the proper placement and articulation of the teeth. In a tissue
supported type of denture,and Stabilization is achieved by a good bilateral balanced
occlusion.




                                  Oddo hinge clasp


              The Oddo hinge clasp modification is primarily
       indicated when anterior abutments have more than
       average labial inclination and, thus, a height of contour
       very near the 'nasal edge The hinge is opened, the
       prosthesis seated, and the hinge closed The tip of the bar
       clasp can be located in a much greater undercut than
       normal. The retentive tip is located in the gingival third of the tooth, and the
       body of the arm is hidden in the labial vestibule Relatively simple adjustments
       in the housing will compensate for minor wear The entire assembly can be
       replaced without remaking the RPD




       Lingual retention in conjunction with internal rests

It is emphasized that the internal rest is not used as a retainer but that its near-
  vertical walls provide for reciprocation against a lingually placed retentive clasp
 arm. For this reason, visible clasp arms may be eliminated, thus avoiding one of
 the principal objections to the extracoronal retainer.
Such a retentive clasp arm, terminating in an existing or prepared infrabulge area
 on the abutment tooth, may be of any acceptable design. It is usually a
 circumferential

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arm arising from the body of the denture framework at the rest area. It should be
  wrought, because the advantages of adjustability and flexibility make the wrought
  clasp arm
preferable. It may be cast with gold or low-fusing chromium-cobalt alloy, or it may
  be assembled by being soldered to one of the higher-fusing chromium-cobalt
  alloys. In
any event, future adjustment or repair is facilitated.
The use of lingual extracoronal retention avoids much of the cost of the internal
 attachment yet disposes of a visible clasp arm when
esthetics must be considered. Often it is employed with a tooth-supported partial
 denture only on the anterior abutments and, when esthetics is not a consideration,
 the posterior abutments are clasped in the conventional manner
One of the dentist's prime considerations in clasp selection is the control of stress
 transferred to the abutment teeth when the patient exerts an occluding force on
 the artificial teeth. The location and design of rests, the clasp arms, and the
 position of minor connectors as they relate to guiding planes are key factors in
 controlling transfer of stress to abutments.
Errors in the design of a clasp assembly can result in uncOntrolled stress to
 abutment teeth and their supporting tissues. The choice of clasp designs should be
 based on biologic as well as mechanical principles. The dentist responsible for
 the treatment being rendered must be able to justify the clasp design used for
 each abutment tooth in keeping with these principles.


                            Incisal cervical prong clasp
The retentive arm runs nearly vertically on the distal part of the tooth from
 distoincisal rest




                        Esthetic solutions in the smile zone

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                                                                       Direct retainers


AESTHETICS OF RPD IN RELATION TO RETAINERS:

Basic types of esthetic direct retainers:

•Intracoronal retainers (Internal attachments): It has better appearance since there is
 no need for buccal and labial clasp arm.

•Extracoronal retainers:

 Prefabricated extracoronal (attachment)

 Esthetic clasps:

Clasp showing may be overcome by the following:

1. Better to use posterior clasp.

2. Use of gingivally approached clasps better esthetically than

   occlusally approached clasps.

3. Designed to utilize the proximal and lingual retentive undercuts.

4. Better to use attachment (instead of clasps).

5. Esthetic solutions:

       Hidden in Teflon-in tube or plastic tube.

       hidden clasps

       Covered by porcelain.

       Made of tooth colored material (metal free clasps): Thermoplastic acetal,
        thermoplastic polycarbonate, thermoplastic Acrylic and thermoplastic
        Nylon.




A- Hiding Denture Clasps


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1- Mesiodistal grip clasps:
It engage only the mesial and distal surfaces of the tooth . They rely upon sound
enamel surfaces and long guiding planes.
2- The Equipoise Clasp :
It relies upon a mesial guide plane with clasp extending around to the distal surface .
3- The RLS lingually retained clasp:
Used for distal extension partial dentures which consists of mesio-occlusal rest a
distolingual "L" bar and distobuccal stabilizer .
4- Dual path or rotational path of insertion :
It involves rigid retentive components and the initial placement of one segment with
the denture being fully seated by rotating the denture into place .
5- Guiding planes :
Guide planes may reduce or eliminate the need for conventional clasp retention in
tooth-borne RPDs. Guide planes themselves serve to provide retention.
6- MGR clasp.
It is an esthetic extracoronal retainer for maxillary canines. Retention is provided by
19 gauges round l-bar and retentive dimple located at distobuccally on the tooth.
Reciprocation is provided by mesial groove or rest and distal proximal plate.
7- Estheti clasp:
The Estheti clasp is recommended for patients with required abutment teeth in the
esthetic zone (incisors and bicuspids). The Estheti clasp design may NOT be indicated
for maxillary canines if the patient is edentulous bilaterally in the posterior.
Advantages
Optimum esthetics,
no attachment maintenance cost.
It utilizes the proximal undercuts and encircles the tooth by 181°. Estheti clasp may be
in the form of Lclasp or C-clasp.
L-clasp: The design consists of the clasp arm extending from lingual minor connector
with an independent reciprocal rest. The L-clasp has greater rigidity than the C-clasp.
C-clasp: It consists of a modified back-action clasp with rest incorporated in clasp.
C-clasp has greater flexibility than L-clasp.
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8- Saddle lock:
The saddle-lock system eliminates facial clasp display while achieving natural
esthetics with superior stability and retention. Saddle lock eliminates facial clasps by
using the available mesial! distal concave surfaces of the abutment teeth for retention
instead of the buccal undercuts.
The benefits of saddle lock
Superior esthetics, without visible clasps,
improved retention with little or no adjustment,
easy vertical insertion that protects abutments,
applicable in most partial denture cases,
simple preparation procedures for less chair time.
Limitations
There is no metal horizontal shoe extension,
the retentive arm is short.
9- Spring clasp ( Twin-Flex technique)
              This consists of a wire clasp soldered into a channel that is cast in the
major connector. Because this clasp is flexible instead of rigid, it does not generate as
much torque when the distal extension is depressed. The ability to adjust this clasp and
its conventional path of insertion provides an excellent design option for retention
adjacent to an anterior edentulous segment.
       Disadvantages of this technique include extra thickness of the major connector
over the wire clasp tang, the extra laboratory steps with increased cost, and difficulty
in repairing the clasp if breakage occurs. (J Prosthet Dent 1997;77:450-2.)
10 - Internally braced clasp
       This design is especially suited for cases, in which anterior abutment tooth is a
crowned mandibular canine and is excellent for Kennedy Class III cases.
       In this crown, a deep cingulum wedge-shaped rest is prepared with occlusally
diverging walls and a rounded floor. An undercut is prepared in the gingivolingual
third of the crown to accept the retentive arm of the RPD. The rest and the clasp arm
emerge from the saddle to occupy their respective areas of the crown. The retentive



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arm engages the lingual undercut and the rest seats accurately in the wedge shaped
preparation.
       Esthetics is improved by the absence of a buccally placed retentive area.
Support is provided by the rounded floor and wedge-shaped walls in the prepared
crown. Retention is provided by the undercut. Bracing and reciprocation are provided
by the internal walls of the preparation.
       Disadvantages
       This design can be used only in teeth with adequate crown height.
       It is generally not applicable in maxillary teeth.
       The abutment tooth must be crowned


11- Equipoise System

        Esthetic retentive concept for distal extension situations proposed by J.J.
 Goodman. The Equipoise semi-precision "E" clasp and precision "C" & "L" clasp
 are specifically designed so that all masticatory forces are oriented down the long
 axis of the tooth.
The Equipoise Balance of Force Principle
      This is accomplished through the use of
 Equipoise Class II Lever design. The Class II lever
 design has the rest (fulcrum) opposite of the retentive
 tip of the clasp (resistance arm) and the denture base
 (the effort arm). The clasp arm always moves in the
 same direction as the denture base while directing all
 forces down the long axis of the retaining abutment
 tooth.
         Advantages
        The Equipoise principle of partial denture design protects, preserves and
 strengthens abutment teeth while directing all masticatory forces down the long
 axis of the abutment tooth. With the Class II lever design you always obtain
 stability during mastication and retention only when needed against dislodging
 forces.




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Equipoise RPD System:
     - Rests placed away from edentulous span

     - 1 mm vertical inter-proximal reduction between abutment and adjacent
         tooth.
     - Optional Bu- Li retentive groove at mid and gingival third junction on
       distal surface of abutment tooth.
     - The retentive clasp terminal extends from the mesial and circles around
       the lingual and distal surfaces of the tooth and engages the distobuccal
       undercut. It is kind to the abutment tooth as it disengages when the partial
       denture is in function.

Disadvantages

Lack of reciprocation and retention can be a problem. Goodman advocated
removal of 0.5 mm of tooth structure from adjacent teeth so that rigid metal of the
RPD framework can extend into the area and provides reciprocation.

The interproximal tooth reduction makes it a caries susceptible preparation.

Mesial proximal plate may introduce torque.

Potential loss of proximal space with a noncompliant patient.

Requires greater surveillance.

During processing, excess acrylic may be allowed to surround the clasp. When
this happens the clasp is not able to flex into the retentive undercuts. Therefore, the
clasp may not seat completely in the mouth or may place unfavourable forces on
the abutment tooth. 'Freeing up' the clasp after processing is difficult and time
consuming. To counter this, stalite spacer is placed around the clasp during
processing. This spacer can be easily removed during finishing and polishing
procedures.


   Equipoise Clasp(E-clasp)

   The E-clasp is a lingual back-action clasp
   that is fully reciprocated, vertically and
   horizontally.


    E-clasp Tooth Preparation

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Rest Preparation

     The occlusal rest is prepared with a
cylindrical diamond stone.

On bicuspids, the rests should be spoon-shaped and encompass 1/3 the
mesiodistal width of the tooth and at least 2/3 of the buccolingual width.

Rests on incisors are prepared over the cingulum or on the incisal edge of the
tooth. The cingulum rest should be at least 1 millimeter deep and one-half the
width of the tooth mesiodistally away from the edentulous area. The incisal
rest should be at least 1.5 mm deep and 1.5 mm wide.

Interproximal Preparation

An interproximal access of at least 1 mm is necessary to give the minor
connector enough strength to support a well contoured rest. This preparation is
made by removing 1/2 mm of enamel from the abutment and 1/2 mm enamel
from the adjacent tooth. A 1 mm tapered
diamond stone is recommended. Rubber wheel
or polish cut surfaces.


Equipoise C&E Milled Design

The C&E Milled Design features the application of a milled abutment crown (
1/2 degree milled undercut) with a precision c-rest ( for stabilization and
reciprocation) and conventional E-clasp ( for retension). This semi-precision
design shows no metal while maintaining proper contact with the adjacent
tooth.


The C&L Precision Attachment

The C&L Attachment was designed specifically
to fulfill Equipoise Class II Lever design
principles. The Counterpoise(C-rest) is a
precision made, pre-fabricated attachment
available in three shapes with corresponding
males. The male is made with a functional
clearance of .15 inches tolerance. The L-Spring is
a removable L- shaped band with ball-point
retention that allows for simplified chairside
replacement.


                                                                 Mostafa Fayad 46
                                                                     Direct retainers




    Impression Procedure

    A quality, single phase impression
    material is recommended. The
    impression tray and material should
    extend into the retromolar and
    tuberosity areas on distal extensions.




12- Esthetic clasp for maxillary canine:

         An esthetic modified circumferential clasp, which resembles a small Class
III gold inlay, is described. An ear-lobe-shaped pattern is made of casting wax
below the height of contour of the tooth and extends the connecting compound into
the embrasure. The lost wax casting process is used to cast the clasp in type-III
noble alloy; this is then soldered to the chrome-cobalt partial denture framework.
Disadvantage

Soldering becomes an additional step in the laboratory procedure,

success of the partial denture is dependant on the soldering procedure.




B - Masking the direct retainer
1- Acrylic or composite coating
A number of techniques that facilitate metal-resin bonding have been reportedly
used to mask the direct retainer with either acrylic or composite. The use of
composite resin to disguise metal clasps is in harmony with current esthetic trends.

                                                                     Mostafa Fayad 47
                                                                         Direct retainers


However, the technique has not been refined primarily because the composite
resins are designed for restorative purposes. Therefore, they are strong but rigid.
           The difficulty of using acrylic/composite resin to veneer RPD metals lies
in the difference between their abilities to flex and their coefficient of thermal ex-
pansion. Non noble metals possess strength and resist flexure. However, acrylic
and composites are subject to greater deformation from physical and thermal
conditions. The composite is brittle past its elastic limit. As a result the abilities of
metals and composites to plastically deform are incompatible. Therefore, the less
flexible the clasp, the more likelihood there is that the bond will endure.
           The various methods used to mask the metallic direct retainer are as
follows:
Macromechanical retention:
Retentive beads and meshwork have been used to retain facing of either acrylic or
composite resin.
Disadvantages

Bulk that is created by adding the veneer will enlarge the total size of the clasp
thus defeating the purpose of disguising the clasp,

bonding is unreliable.

GAP formation and micro leakage when used in combination with composites
Micromechanical retention:
It involves air borne particle abrasion. This helps to improve retention between the
alloy and the resin.
Disadvantages

Bond strengths obtained after the use of micro mechanical systems are insufficient
especially after thermal conditioning.


2- Silica coating:
          This technique is based on adhesion of resin to silane bonding agents.
These silanes, however, failed to bond directly to metals. The reason for such a
failure is the lack of preferred substrate and groups required for a good chemical
bond of silane to metal. Such end groups maybe Si-OH and AI-OH, which are not
readily supplied by the alloys used.
                                                                         Mostafa Fayad 48
                                                                         Direct retainers


         This new technique involves coating the metal with silica intermediate
layer (SiOx-C) that bonds to metal and also supplies the -OH group for silane
bonding. The tribochemical effect of air borne particle coated with silicic acid on
the alloy surface renders it amiable to silane bonding agents. This coating allows
the development of superior bond strengths to electro etching or chemical etching.
Hence, even in the presence of the flexing retentive clasps the bond strengths are
significant to prevent debonding.
Disadvantages
Lack of long-term controlled studies limits the use of this technique.
C- METAL-FREE CLASPS

1- Dental D clasps

They are the perfect solution to unsightly metal clasps either on chrome or acrylic
dentures and can be prescribed for new or existing dentures. Dental D comes in a
choice of shades to match the patients own teeth or pink shades to match the patients
gum. The Dental D clasps are very tough, flexible and does not distort.

2- Opti= flex invisible clasp partials

With the Opti= Flex acetyl resin clasps, metal-free, lightweight partial dentures that
provide natural esthetics and a comfortable fit can be designed. Using the Opti= Flex
Coating applied to metal clasps, it is possible to give new or existing metal partial
dentures a new esthetic appeal. It is available in 16 tooth-colored shades (matched to
the base Vita Shades) and hence Opti- Plex can meet every patient's esthetic
requirements.

3- Flexite plus cast thermoplastic

       Flexite Plus 'Flexible' partial dentures eliminate the use of metal, providing
patients with a metal partial denture alternative. Flexite Plus is fabricated from a
flexible thermoplastic material that is available in three tissue shades. The material is
monomer-free, virtually unbreakable, lightweight, and impervious to oral fluids.
Flexite Plus may also be combined with a metal framework to eliminate the display of
metal labial clasps.
                                                                         Mostafa Fayad 49
                                                                       Direct retainers


4- NaturalFlex: Based on acetyl resin technology.

Available in 20 shades with three pink hues. The tooth or tissue coloured resin clasps
though as slim as those made of metal provide superior strength. They are flexible and
light weight. They are also up to 20 times harder than restorations fabricated from
standard acrylic materials.

5- Proflex clear wire clasps:

Clear wire is an excellent new way to fabricate clear, strong, flexible clasps in
minutes. This new material and technique can be used to make T-bars, l-bars, Roaches,
Acers, and most other types of clasps. It can also be used to add or repair clasps in an
existing partial denture. It should be noted that the technician must have a good
working knowledge of partial design before trying to incorpo rate a Pro flex Clear
Wire technique into their work.

6- Smile-Rite partials:

Smile Rite is a high strength acetyl resin-polymer used for making tooth coloured
clasps on cobalt-chrome alloy partial frameworks.

The combination of Smile Rite with a metal frame gives patients the proven long-term
reliability of a cobalt-chrome alloy framework with the durability and esthetics of
Smile-Rite tooth coloured clasps. Existing metal frameworks can be retrofitted with
SmileRite clasps for esthetically conscious patients. Smile Rite is colour stable and is
resistant to staining and plaque buildup.

The high strength of Smile Rite makes it possible to fabricate the entire framework
metal free. The framework can be made from either tissue colour or tooth colour
monomer-free Smile-Rite acrylic.

7- DUET CLASPS

Estheti-fl ex 'Duet': Developed with the esthetically driven patient in mind, the Estheti-
Flex 'Duet' combines the support of a Vitallium or Titanium cast framework with the

                                                                       Mostafa Fayad 50
                                                                         Direct retainers


comfort of Estheti-Flex tooth coloured clasp system for the ultimate in function and
esthetics. The Estheti-Flex 'Duet' appliance is recommended for patients requiring cast
rests for support combined with Vita shaded or clear resin clasps for improved
appearance in the esthetic zone)

8- Themoflex thermoplastic clasps

       Thermoflex is an improved acetal resin system that brings the many benefits of
metal-free restorations without the pitfalls associated with acrylic)15]

Thermoflex is so flexible that it can flex around the largest tooth, and then use its
superior elastic memory to cling deeper into the undercut for a rigid functional hold.

It is a Hypoallergenic, monomer-free material ideal for patients with allergies or
patients that cannot tolerate a metal partial framework. It is hydrophobic; hence does
not absorb water or saliva.

Thermoflex has unsurpassed durability and it bonds well with conventional acrylics, as
well as, to itself, which means it can be repaired, relined or rebased. It is available in
19 shades, 16 tooth coloured and 3- tissue coloured. The Thermoflex partials are
injection molded using heat and pressure which makes the final product dense




                                                                         Mostafa Fayad 51
                                                               Direct retainers




                      Flexible tooth colored clasps




Combination of cast metal and flexible tooth colored clasps.
                       Acetal Tooth-colored Clasp




                            Check Mate Denture

Pain -less d enture sy stem by Dr.S akurai. Certain adjus tment with a
pilot d enture.
We can realize denture to be able to fit clos ely w ith high technique of
plas tic molding.




                                 FIN    Denture

Fin D EN TU RE s tick to the jaw when anterior lingual occlus al
press ur e.
Becaus e FIN D ENTU RE is attached w ith Fin V alve


                                                               Mostafa Fayad 52
                                                                     Direct retainers


and it is clinging to the jaw. Th is clingin g function ma ke patien t bite
who le apple.




           Clasp                                            under cut

           Aker's clasp                                     0.01 inch

           Ring Clasp                                       0.02 - 0.03 inch

           Back Action Clasp                                0.01 0.02 inch
           Reverse back action                              0.01 0.02 inch




Bios clasp system
In the Bios clasp system the retentive force of the clasp is related to the depth of
  undercut and the length of the clasp arm .
The retentive force of a clasp arm is dependent on the following factors:
- The length from its tip to its point of attachment
- The shape of its cross-section
- The metal alloy used
- The depth of the undercut



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The basis for all clasps is a standard wax shape. It has a uniform taper and its
 cross-section forms half of an elipse with a width-to-height ratio of 10:8.
The length of the clasp is measured with a device built similar to those used for
 measuring the mileage on maps. In order to form a clasp arm with the desired
 retentiveness after the depth of the undercut and the length ofthe clasp have been
 determined, it is only necessary to read from the table how many millimeters to
 cut from the tip of the standard wax shape.




Bios Clasp System
        In the Bios system the retentive force ofthe clasp is related to the depth of
 undercut and the length ofthe clasp arm. All clasps should exert almost the same
 retentive force.
        This standard shape has made it possible to draw up a table in which the
 retentive force, the depth of undercut, the clasp length, and the dimensions of the
 clasp crosssection are specified.
The retentive force of a clasp arm is dependent on the following factors:
     - The length from its tip to its point of attachment
     - The shape of its cross-section
     - The metal alloy used
     - The depth of the undercut
         The basis for all clasps is a standard wax shape. It has a uniform taper and
 its cross-section forms half of an elipse with a width-to-height ratio of 10:8.
The length of the clasp is measured with a device built similar to those used for
 measuring the mileage on maps. In order to form a clasp arm with the desired
 retentive¬ness after the depth of the undercut and the length ofthe clasp have
 been determined, it is only necessary to read from the table how many
 millimeters to cut from the tip of the standard wax shape.




                                                                      Mostafa Fayad 54
                                                                     Direct retainers


The Bios standard clasp arm shape serves as a basic element for all types of clasps.
The flexibility 01 a clasp arm is determined by how much length is removed from
the small end of the pattern.



The exact depth of undercut for the previously drawn
clasp tip is determined with a special measuring device.
The undercut depth can be read directly within a range of
0-1 mm.




Stress and its control by clasp design

 Retention should not be considered the prime objective of design:
      (1) The main objectives should be the restoration of function and appearance
          and the maintenance of comfort, with great emphasis on preservation of the
          health and integrity of all the oral structures that remain.
      (2) The retentive clasp arm is the element of the RP.D that is responsible for
          transmitting the most of the destructive forces to the abutment teeth. A
          removable partial denture should always be designed to keep clasp retention
          to a minimum yet provide adequate retention to prevent dislodgment of the
          denture by unseating forces.
      (3) Close adaptation and proper contour of an adequately extended denture base
          and accurate fit of the framework against multiple, properly prepared guide
          planes should be used to help the retentive clasp arms retain the prosthesis.
              By exploiting retentive potential in various widely separated areas of the
          mouth, both support and stability may be enhanced at the same time that
          stress is effectively reduced.


Biomechanical Considerations in Clasp Design
         1. The simplicity of the clasp: The simplest type of the clasp that will
          accomplished the design objectives should be employed




                                                                     Mostafa Fayad 55
                                                               Direct retainers


  2. Clasps should be designed to minimize interference with normal
    stimulation of gingival tissues and demote plaque formation• to preserve
    periodontal health.
  3. There should be at least 5 mm. clearance between vertical components,
   e.g. minor connectors, proximal plates, etc.,
  Note: The reason for the different distances of major connectors from
   gingival margins is that maxillary casts are beaded to insure positive
    adaptation of the major connector whereas mandibular casts are relieved to
    prevent contact of the major connector against the delicate mucosa.
  4. There should be at least 3mm. Clearance between the approach arm of
    bar clasps and the gingival margin.
  5. Maxillary major connectors comprising part of a clasp assembly should be
   located at least 6mm from the gingival margins.
  6. Mandibular lingual bars comprising part of a clasp assembly should be
    located at least 3mm from the gingival margin.
  7. Qualities of clasp:
        a- Clasp should have good stabilizing qualities, remain passive until
           activated by functional stress, and accommodate a minor amount
           of movement of the base without transmitting a torque to the
           abutment tooth. The more flexible the retentive arm of the clasp,
           the less stress is transmitted to the abutment tooth.
        b- As the flexibility of the clasp increases, both vertical and lateral
           stresses transmitted to the residual ridge increase.
8. Materials and type of alloy used in clasp construction:
   a. A clasp constructed of chrome alloy will normally exert greater stress on
      the abutment tooth than gold clasp, all other factors being equally. To
      compensate for this property, clasp arms of chrome alloys are constructed
      with a smaller diameter than a gold clasp would be to accomplish the
      same purpose.
   b. Wrought wire is more resilient than the same alloy of identical diameter
      and length in cast form, because of its internal structure.
9.Strategic clasp positioning (Location of clasps) as a method of stress control:


                                                                Mostafa Fayad 56
                                                                      Direct retainers


         o Clasps should be strategically positioned in the arch to achieve the
           greatest possible control of stress and leverages.
         o Clasps could be placed at each end of the denture, so that the resultant of
             their forces is near the center of gravity of the denture. Biologically, this
             clasping distribution is not well accepted, as more teeth are prone to
             coverage. Instead, two clasps diagonally placed can be used.
         o If two clasps are insufficient and the denture tends to rock about the line
           joining the two clasps, a third clasp placed as far as possible from the
           others is added.
         o Molars are the most suitable teeth for clasping due to their contour,
             strength and size, followed by premolars, canines then upper central
             incisors.
         o Incisors specially lower incisors and upper laterals are not preferred due
           to esthetic and mechanical reasons. Tooth supported dentures may
             require more clasps to distribute the load on more teeth.
Quadrilateral configuration:
              It is indicated most often for class III arches particularly when there is a
        modification space on the opposite side of the arch (Fig. 11-9). When four
        abutment teeth are available for clasping, and the partial denture can be
        confined within these four clasps, all leverage is neutralized.
Tripod configuration:
             It is used primarily for class II arches if there is a modification space on
        the dentulous site. When the distal abutment on one side of the arch is
        missing, the inevitable lever is created by the distal extension base. In this
        case, the leverage may be controlled, to some degree, by creating a triangular
        pattern of clasp placement.
Bilateral configuration (Kennedy class I):
             When two distal extension bases must be dealt with, the designer has
          little choice but to clasp the two distal abutments.
                  In this circumstance, the clasps exert little neutralizing effect on the
          leverage-induced stresses generated by the base, and they must be
          controlled by some other means.

Unilateral prosthesis

                                                                       Mostafa Fayad 57
                                                                       Direct retainers


            Leverage per se is not a problem with the unilateral type of edentulous
     span . However, torsional stress on the abutments is generated by the prosthesis
     because of its tendency to rotate in a buccolingual plane. The conventional
     solution is to cross the arch with a major connector and to clasp teeth on the
     contralateral side, thus making the prosthesis, in effect, bilateral in design.
     Ordinarily this is the preferred approach to the problem. If the unilateral design
     must be used, all four clasp arms should be made retentive in order to minimize
     the tendency of the prosthesis to rotate around a line that extends mesiodistally
     through the two abutment teeth.


11- Selection of Clasp form:
     The form of any clasp is determined according to the following factors:
         1-Position of the tooth.
                    Clasps on anterior teeth should be gingivally approaching.
              Occlusally approaching clasps on premolars should start distally to
              keep the body of the retentive arm on the distal half of the buccal
              surface to be less visible.
         2-Condition of the tooth.
                      Wrought wire and gingivally approaching clasps are preferred
              for teeth with questionable periodontal support.
         3-Position of the edentulous area.
                     In bounded areas, occlusally approaching clasps provide good
              retention, bracing and stabilization. In free-end areas, Flexible rather
              than rigid clasping is preferred to provide retention and allow slight
              movement of the denture base without stressing the abutments. The
              RPI, I-bar, RPA, RLS, combination clasps, back action, reverse back
              action or reverse circlet clasps can be used.
         4-Axial inclination of the abutment.
               Ring clasp is preferred on tilted molars to prevent further tilting.
         5-Position of occlusal rest.
                    Rests are placed near to bounded edentulous areas, and far from
              free-end areas.
         6-Position of retentive undercut.
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                                                                     Direct retainers


                    Retentive undercuts are selected far from bounded edentulous
              areas, and near to free-end areas.
           If the abutment tooth exhibits an undercut on the disto-buccal side, then
                  a reverse circlet clasp can be used.
           If the undercut is on the mesio buccal side, a combination wrought wire
                  clasp, RPI clasp or back action can be used.
           If the undercut is on the distolingual side, RLS clasp can be used.
           If precision attachments or rigid clasping are used to retain a class I
                  partial denture, a stress breaker should be used.
12- Leverage and Esthetics is clasp design:
                    A fundamental aspect of clasp design is that the arms should be
           placed as low on the crown, within limits, as the survey line will permit, in
           order to reduce the effect of leverage.
13- Number of the clasps:
                    The retention is not proportional to the number of clasps.
           Satisfactory amount of retention, is that required to keep or just to retain
           the denture in its place during function and rest.




                                                                     Mostafa Fayad 59
                                                                       INDIRECT RETAINERS



                               INDIRECT RETAINERS


 Rational for indirect retention
 Tooth-tissue supported partial dentures are subjected to vertical displacing forces
       acting in an occlusal direction. These forces may totally displace the denture if
       the direct retainers are not functioning adequately. However if the direct
       retainers are adequate, rotation of the denture around a fulcrum axis rather
       than total displacement occurs. This rotation is counteracted by the unit of the
       partial denture called "Indirect retainer".
 In tooth supported partial dentures; tissue away movement of the prosthesis is
       prevented by the action of direct retainers and rests placed on the abutment
       teeth (self indirect retainer).
 In mucosa supported partial dentures;(full palatal coverage) tissue away
       movement of the prosthesis is prevented by mechanical means (clasps) and by
       the action of physical means of retention on a well fitting denture base and the
       connector (direct indirect retention).


Definitions:
 Indirect Retention: The resistance to rotational movement of a tooth-tissue
      supported denture base and palatal major connector away from the denture
      foundation area when occlusal forces (sticky foods) are applied to the denture
      base.
 Indirect Retainers are “components of removable partial denture that are used to
    reduces the tendency of the denture to rotate in an occlusal direction about the
    fulcrum axis”.
  The fulcrum line (prothero 1916) is an imaginary line, connecting occlusal rests,
    around which a partial removable dental prosthesis tends to rotate under
    masticatory forces. The determinants for the fulcrum line are usually the cross
    arch occlusal rests located adjacent to the tissue borne components.
  It is a theoretical line passing through the point around which a lever functions
    and at right angles to its path of movement




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                                                                     INDIRECT RETAINERS



 Direct retainers are retaining elements (clasps) used to retain near ends of partial
   dentures. However, Indirect retainers are supportive elements (rests) used to
    retain far ends of partial dentures
 This movement of the saddle may be caused by the action of sticky food or by
   gravity in the upper jaw. Indirect retainers do not prevent displacement towards
   the ridge. This movement is resisted by the occlusal rest on the abutment tooth and
   by full extension of the saddle to gain maximum support from the residual ridge.
 The concept of indirect retainer is advanced by Dr W.E.Cummer as means of
   resisting rotational movement
       Movement of a distal extension base RPD in function can be summarized as
rotation around:

      The 1st fulcrum             The 2nd fulcrum                The 3rd fulcrum
      Horizontal plane             Sagittal plane                 Vertical plane
 extends through the two extends         through      the   located in the vicinity of
 principal abutments        occlusal rest on the terminal   the midline just lingual to
        (Fulcrum line)      abutment and along the          the anterior teeth.
                            crest of the residual ridge
                            on one side of the arch.
 controls the rotational controls the rotational            controls the rotational
 movement of the denture movements of the denture           movement of the denture
 in the sagittal plane      in the vertical plane           in the horizontal plane,
 -    denture      movement – rocking, or side to side,     - flat circular movements
 toward or away from the movements over the crest           of the denture.
 supporting ridge).         of the ridge).




       The degree and direction of the denture base movement are greatly influenced by
the quality of the supporting residual ridge, the design of the RPD and the extent of the
forces exerted on the denture during function




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                                                                          INDIRECT RETAINERS




Indications for Indirect Retainers
       Indirect retainers are used in removable partial dentures having one or more
   free extension bases as in Kennedy class I, class II and long span class IV.
      Indirect retainers may also be used in Kennedy class III where a long
   edentulous span is bounded with one distal abutment having guarded prognosis.
   The loss of this abutment would create a distal-extension base.

Functions of indirect retainers:

       The main function is to resist occlusally displacing forces acting on the free end
saddle by creating a resistance on the opposite side of the fulcrum axis.

Auxiliary Function of Indirect Retainer:
        1- Reduce anteroposterior tilting on abutment tooth, especially on an
        isolated tooth.
        2-    Aids in stabilization against horizontal movement of the denture.
        3-    Splints anterior teeth against lingual movement.
        4-    Acts as an auxiliary rest against vertical forces.
        5- Serves as a third point of reference when orienting the framework
        during reline procedures.
        6- It may provide the first visual indications for the need to reline an
        extension base partial denture. Deficiencies in basal seat support are
        manifested by the dislodgement of indirect retainers from their prepared rest
        seats when the denture base is depressed and rotation occurs around the
        fulcrum.

   The indirect retainer works as mechanical disadvantage. by incorporating indirect
   retainer in free end situation , the resistance to effort arm is increased.
   Mechanical disadvantage = resistance arm / effort arm
      = distance between clasp and IR / distance between point of effort and IR



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                                                                        INDIRECT RETAINERS




Factors Influencing the Effectiveness of Indirect Retainers
     Factors that influence the proper function of indirect retainers are:
1- Effectiveness of the direct retainers:
          For the indirect retainers to be effective, the direct retainers must prevent
     the rests and dentures from being lifted, as this lift causes displacement rather
     than rotation of the denture base..
2- Proper location of indirect Retainers:
     1- Well-supported indirect retainers should be placed as far from the fulcrum
        line as possible. The greater the distance, the more effective is the indirect
        retention.
     2- A perpendicular line projecting anteriorly from the fulcrum axis is the most
        effective location of indirect retainers and affords the best resistance against
        vertical dislodging forces.




     Although the most effective location of an indirect retainer is commonly in the
vicinity of an incisor tooth, that tooth may not be strong enough to support an indirect
retainer and may have steep inclines that cannot be favorably altered to support a rest. In
such a situation, the nearest canine tooth or the mesio-occlusal surface of the first
premolar may be the best location for the indirect retention, despite the fact that it is not
as far removed from the fulcrum line. Whenever possible, two indirect retainers closer to
the fulcrum line are then used to compensate for the compromise in distance.



3- Rigidity of the denture frame:
             The minor connector joining the indirect retainer to the framework
        should be rigid. Flexing of the connector multiplies rather than dissipates the
        applied forces.



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                                                                        INDIRECT RETAINERS


4- Effectiveness of the supporting surface:
     1. Indirect retainer in the form of rest should be placed in a definite, properly
        prepared rest seat that allows transmission of the forces along the long axis of
        the tooth without slippage of the rest or movement of the tooth.
     2. Indirect retainers should never be placed on weak teeth or on inclined
        surfaces.
5- The length, fitness and the extent of the distal extension base:
     1. Well fitted and adapted base provide more effective indirect retention.
     2. The shorter the base the more effective is the indirect retention.


Forms of indirect retainers:


          Indirect retainers may have one of several forms; each is effective in
     proportion to the degree of support and the distance from the fulcrum axis. These
     forms are


            A- Indirect Retainers Used In Mandibular Partial Dentures:


1- Auxiliary occlusal rests: This is the most common form of indirect retainers. It is
  placed on an occlusal of the tooth as far away from the fulcrum axis as possible on
  mesial marginal ridges of first premolars..
2- Canine extension from occlusal rests: A finger like extension arising from the
  principal premolar rest and placed on the prepared cingulum of the adjacent canine
  tooth. It indicated in long distal extension cases, as it is used instead of locating of
  the indirect retainers on an incisor tooth which may not be strong enough to support
  the denture




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                                                                          INDIRECT RETAINERS


3- Canine rests (cingulum rest): The canine rest is used as an indirect retainer in
  cases where the mesial marginal ridge of the first premolar is too close to the
  fulcrum axis.
4- Principal occlusal rest of modification area:
       The occlusal rest on the anterior abutment of modification space provides indirect
retention.

5- Auxiliary rests at the terminal ends of lingual plate or Kennedy bar:
       The continuous bar is a metal band passing continuously over the cingulum of
anterior teeth, ending at each side with terminal auxiliary occlusal or canine rests. The bar
itself is not considered as an indirect retainer because it is located on the unprepared
lingual surfaces of anterior teeth. However, the terminal rests on either side are the
components providing indirect retention.
6- Lingual plate or continues bar
       The bar itself is not consider indirect retainer as it is placed on un prepared tooth
surface , however the terminal rests on either side are providing indirect retention .
7- Embrasure hooks


              B- Indirect Retainers Used in Maxillary Partial Dentures:


     Auxiliary occlusal rests, canine extension from an occlusal rest, terminal rests of
the continuous bar and cingulum rests on maxillary canines are used as maxillary
indirect retainers. In addition, there are other forms of indirect retainers that are
supported by the palate, these are:
1) Cummer arm:
       It is a maxillary indirect retainer that extends either from the denture base or
from a palatal major connector and rests on a canine tooth. This type exerts excessive
load on the supporting tooth causing movement of the tooth labially. It is also liable to
distortion.



                                                                                 Mostafa Fayad 6
                                                                          INDIRECT RETAINERS


2)      Palatal arm
        It is an extension of the palatal major connector on the opposite sides of the
fulcrum line. The projections may initiate bad tongue habits, interfere with speech,
and are liable to cause irritation of the palatal mucosa underneath the end of the arm..


3)      Anterior palatal bar
        The anterior palatal bar is a maxillary major connector provides indirect
retention for a posterior denture base as in Kennedy class I and II. However, the
anterior palatal bar is not well tolerated by some patients because it crosses the rugae
area.
4)      Posterior palatal bar
        The posterior palatal bar is a maxillary major connector that gains support from
the posterior palatal region. It acts as an indirect retainer for long span class VI
denture bases
5)      Palatal strap and Rugae support
        The anterior palatal strap is a maxillary major connector, which may provide
indirect retention for class I and II bases because it covers a considerable area of the
hard palate. However, tissue support is less effective than positive tooth support .
C) Indirect Retainers Used in Maxillary and mandibular Partial Dentures


     1- indirect retention from major connector
        In tooth tissue support partial denture in which the indirect retention is achived
by covering the tissue areas anteriorly for support. As rugae support.
        Well fitting denture bases of upper class I RPD connected by broad palatal
plate seldom need anterior indirect retainers. Physical retention gained by the bases
and connector, and physiologic retention affected by upward thrust of the tongue
retain the posterior ends of the denture. This is actually direct retention that
compensates absence of clasps at posterior ends .
     2- Direct-indirect retaintion


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                                                                        INDIRECT RETAINERS


       Some times the reciprocal arm of direct retainer located anerior to the fulcurum
line and act as indirect retainer


   3- Modification areas
If occlusal rest on the secondry abutment is far from the fulcurum line it can act as an
indirect retainer




I- Indirect retainers placed on tooth structure:
1-Auxillary occlusal rest
2- Canine extension from occlusal rest:
3- Canine (cingulum) rests:
4- Secondary lingual bar:
5- Cummer arm:


II- Indirect retainer placed on the palate (for maxillary denture only)


1- Palatal arm:
2- Anterior palatal bar:
3- Posterior palatal bar:
4- Rugae support:
5- Palatal strap:




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                                                                                  Attachments in RPD


         Attachments And Their Use In Removable Partial Denture
Is a retainer consisting of two or more parts, one part is connected to a root, tooth or implant
and other part to the prosthesis.

A precision attachment is an accurately fitting interlocking device for fixing removable

restoration to the natural teeth

• Many names have been given to describe these attachments as male and female, patrix

and matrix, key and keyway, parallel, frictional, internal and slot attachment.

Requirements for success
– A well motivated patient with good oral & physical health

- A good level of knowledge of attachment & team work between the clinician & technician

- Regular adjustment of the attachment & relining of the prosthesis

- The patient must be aware of the cost and time required for this type of treatment

Indication of Precision Attachments
There are several situations in which the use of attachment is indicated

- use of resilient attachment to relieve stress.

¬- To accommodate mal-aligned fixed partial denture abutments.

- Esthetics in case of horizontal or vertical bon loss of abutment teeth

- Support in case of “RPD, free end saddle, splinting , over denture

Contra indication
a - Abutment not suitable for attachment retainer

- short clinical crown - Narrow bucco-lingual crown

-Large pulp horn       -Insufficient bone support

b - Improper mucosal condition

-No room for attachment (vertical and horizontal)


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                                                                                   Attachments in RPD


- Inflammation       - No bone support ( wiry ridge)

c-        Greater coast to the patient.

Advantages of precision attachment:-
        1- Better esthetics due to the labial or buccal clasp arms on canines or premolars are not
     required.

        2- Vertical and horizontal lodes are applied more directly to the abutment teeth than by
     clasps or rests. This advantageous only if the supporting structures of this tooth are perfect.

       3- The efficiency of retention is not affected by the contour of the abutment tooth.

       4- The number of the component of the denture is reduced and hence tolerance should be
     better.

        5- When used with lower free end saddles, posterior movement of the denture is
     prevented.

       6- Their use may be indicated when retentive clasp arm reciprocation can not be achieved.

       7-Positive retention and stability

       8- Reduced bulk of the prosthesis

Disadvantages of precision attachment:-
       1- Extensive preparation of all abutment teeth, with construction of the necessary crown
       or onlays.

       2- When the crowns of the abutment teeth are small or short, this attachment can not be
       used.

       3- Teeth with large pulps can not be used.

       4- It can not be used for free end saddle due to rigidity of the union between the tooth and
       saddle.

       5- Owing chair and laboratory time involved and the high coast of the attachments.

6-        No sufficient space for accommodation

7-        Expensive cost and need highly qualified technicians



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                                                                                    Attachments in RPD


         1- Since the principle of the internal attachment does not permit horizontal movement,
all horizontal, tipping, and rotational movements of prosthesis are transmitted directly to the
abutment tooth. The internal attachment therefore should not be used in conjunction with
tissue support distal extension denture base unless some form of stress breaker is used
between the base and the rigid attachment.

        2- The Intracoronal attachment engages the vertical walls built into the crown of the
abutment teeth to created frictional resistance to removal.

Classification of attachments
1 – according to manner of fabrication :-

         A ) semi – precision attachment             B – Precision attachment

2 – according to location

         A ) Intra coronal attachment                   B ) Extra coronal

        C ) Radicular / intraradicular stud type        D )Bar type         E) Auxillary

3 - According to behavior during action

A ) class I :- -rigid , non resilient attachment             -used with bounded saddle

               - -Frictional grip intra coronal attachment

               -e.g. : - -Dalbo bar unit , -non resilient dalbo stud attachment ,- non resilient Ceka

B ) class II :- - Allow for vertical resiliency         -used with short free end saddle

            -e.g.:- schatzman intra coronal attachment, dalbo extra coronal attachment,

           CEKA extra coronal attachment , dalbo stud attachment , CEKA stud attachment

C ) classIII :- - allow for hinge movement             - used with long span free end saddle

               – e.g. :- -dalbo extra coronal attachment , resilient dalbo stud attachment,

                       resilient CEKA stud attachment

D )class IV :- - allow for hinge & vertical movement         - used with long span free end saddle

                -eg :- -as class III

E) class V :- -vertical & hinge movement as well as buccolingual rotation

              -used with long span free end saddle


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                                                                                  Attachments in RPD




4- According to retention manner

A) Frictional :-

. Is resistance to relative motion oe two or more surface s in intimate contact with each other

. E.g. :- The Beyeler attachment

. Caution :- if attachment is over polished , frictinal retention may be lost

B) Mechanical :-

. Is resistance to the relative motion of two or more surfaces due to a physical under cut

. E.g. :- The Hannes Anchor attachment

.Caution :- if the plunger of the a   achment doesn̕t engage the female undercut there will be no
Mechanical retention

C) Frictional & Mechanical

. Combines both features of frictional& mechanical retention

E.g. :- The Score-PD attachment

d)Magnetic :-

. is the resistance to movement caused by a magnetic body that attracts certain materials by
virtue of a surrounding field of force produced by the motion of its atomic electrons and
alignments of its atoms

Caution :- it does not provide lateral stability and contra indicated for flat ridges

e) Suction : -

Is a force created by a vacuum that causes a solid object to adhere to a surface .

E.g. :- a well fitting denture

Caution :- Most removable restoration require a periodic check of tissue condition and if
deficiency occur reline it




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                                                                                  Attachments in RPD




1 – according to manner of fabrication :-

      A) semi – precision attachment

             - It is fabricated in the lab by the direct casting of wax pattern, plastic, or
             refractory pattern

              - they are considered " semi – precision" since in their fabrication they are
             subject to inconsistent water/powder ratio , burn out temperature , and other
             variables so resultant component varies to a small degree

             Advantages: -

             1 – Economy ( low cost)

             2 – Easy fabrication

             3 – Ability to be cast in a wide choice of alloys without the problem of co
             efficiency differences between the cast and machined alloy

             Disadvantages: -

             1 – liable for dimensional changes during casting (less accuracy)

             2 – difficult to repair

Blatterfein classified the laboratory-fabricated attachments according to their
occlusal outline form into:

(a) Locking types Semiprecision attachments. These includes:

i- Dovetail rest system.

ii- Circular rest system.

(b) Non-locking types Semiprecision attachment: In the form of rectangular rest
system.




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                                                                       Attachments in RPD


B) Precision attachment

     - They are ready made & their component are maintained in special meta alloys
     under precise tolerance & these tolerances are within 0,01mm

     - One component is soldered to metal crown & other to frame work

     - They are very accurate and easily repair

     According to retention mechanism between the two components of the
     attachments, two types are available:

     (a) The active friction grip attachments: These include an adjustable spring. This is
     usually accomplished by designing a split patrix so that part of it forms a leaf
     spring, which can be opened to compensate wear to give retention

     (b) The active snap grip attachments: In this group, the active element consists of
     a spring -loaded plunger, a split ring or U-spring, which engages in a prepared pit
     or groove.



     Advantages: -

     1 –give a splinting effect & less wear on abutment

     2 – The load fall down with the long axis of the abutment

     3 – Standard parts which allow the component to be interchangeable

     4 – Not affected with the contour of the abutment

     5 – More tolerated by the patient

     6 – Eliminate the food stagnation

     Disadvantages: -

     1 – Extensive preparation to abutment

     2 – Need long chair side time

     3 – Wear & lose retention by time

     4 – Very expensive


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                                                                                 Attachments in RPD


2 – According to location :

        A ) Intra coronal attachment

    Usually called as an internal attachment or a precision
a   achment. It is developed by Dr Herman E.S.Chayes in 1906.

An intracoronal attachment is one which is contained within the
normal contours of the crown portion of a natural tooth. The
placement of the attachment requires that the abutment tooth be restored with a full or partial
coverage (3/4) crown.



    Made of

         I- Matrix ( metal receptacle) : -

           *usually contained within the normal or expanded contour of the crown of abutment

           *it may also be attached to the fitting surface of denture framwork

         II- Patrix ( closely fitting part ) :-

                *usually attached to pontic or denture framwork

                *it is always solid (not hollow)

  - Their function is to provide positive direct retention for a partial denture. They may prove
more retention than the clasp, but the clinical situation in which they are used required careful
assessment and the standard of the patient oral hygiene must be good. OSBORNE

-    It is supply in two forms : readymade attachment (Precision attachment) or Fabricated
by the dental technician (semi – precision attachment )

        Design:- - Support is achieved by floor of matrix

                  - Bracing is achieved by walls of matrix

                 - Retention is achieved by friction

            - An intracoronal attachment usually requires a box preparation to allow the
            attachment to fit within the crown contour. if it is not possible to create a box
            preparation that will totally incorporate the female element , then extra coronal
            attachment should be considered

                                                                                    Mostafa Fayad 7
                                                                        Attachments in RPD


Advantages:-

   1 – stress fall near the long axis of the tooth

   2 – excellent support & bracing

Disadvantages:-

   1- Not used with young patient

   2 – Not used with short crown



Types

    A) Universal Intra Coronal Attachment

         - The IC attachment is a popular spring loaded retaining attachment that
        provides free movement for abutment protection without requiring an
        abutment crown.

        -    The IC a achment requires a 180 degree reciprocal lingual arm. The
        attachment consists of a male anchor and female inlay.

         - It is made of a stainless, chrome-alloy like those used for casting partials. It
        will not tarnish or corrode, and when properly installed, will not malfunction
        even after years of wear.

        - Other benefits include no pulpal involvement, no gingival retraction before
        impressions, easy to adjust at the chair, and this is a reversible procedure.

    B ) McCollum attachment

        - retention by frictional grip

        -rigid used with bounded saddle

    C) Crisman's attachment

         Retention by friction & mechanical through :-

         1 – Active friction grip ( friction)

         2 – Active snap grip { mechanical - more retention}


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                                                                                   Attachments in RPD


               - rigid, used with bounded saddle

        D ) schatzman's attachment

               - retention by active snap grip       ( frictional & mechanical )

               - resilient so used with free end saddle

               - the patrix is attached to a spring to increase resiliency

   B ) Extra coronal

     - Extracoronal Precision attachments are normally resilient to
    allow free movement of the prosthesis to distribute potentially
    destructive forces or loads away from the abutments to
    supportive bone and tissue. Three distinctive movements are
    defined in function:     (1) Hinge,

                               (2) Ver    cal, and

                               (3) rota   onal

    - The fewer abutments remaining, and the weaker the abutments are, the greater the
    need for resiliency or free movement to direct the forces away from the abutments to
    the supportive bone and tissue via the base of the prosthesis.

    Indication

    - Retaining abutments are small to avoid over-contoured intracoronal attachment
    abutments and/or pulpal exposure

    - used for patients with limited manual dexterity, or the prosthesis has a difficult path
    of insertion and removal.

    Design:-

    - The matrix or patrix is attached to outside contour of abutment

    Advantages:-

    1 – The normal tooth contour can be maintained

    2 – Minimal tooth reduction & the possibility of devitalizing the tooth is reduced

    3 – The path of insertion is easier for patient with dexterity problems


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                                                                              Attachments in RPD


       4- Intracoronal females in retaining abutments will collect food and present problems
       when the patient attempts to seat the intracoronal retained prosthesis.

       Disadvantages:-

       - It is ,however , more difficult to maintain hygiene with extra coronal attachment and
       patients should be instructed on the use of dental floss and hygiene accessories.

       Types

       A ) Dalbo attachment ( ball & socket ) :-

             - the patrix is attached to the abutment

             - the ball "patrix" give a hinge movement & the spring
             in the matrix give a vertical resiliency

             -so it can be used with a free end saddle

       B ) Ceka attachment

              - The Traditional Ceka and Ceka Revax systems
             provide for hinge, vertical, and rotational movements
             to provide maximum abutment protection.

             - Each attachment consists of three angulations of
             plastic female profiles with precision metal insert,
             male spring pin, and retention component. The three angulations allow the user to
             design the case for the patient’s needs.

             - The matrix is attached to the abutment , -the patrix has a split in it's center to
             enhance friction , - a spacer ring can be placed between matrix & patrix to increase
             vertical resilience

Adhesive prosthetic techniques are innovative methods for employing extracoronal
attachments. They enable cobalt chrome appliances to be retained without
clasps therefore achieving optimum aesthetics .

The adhesive units are retained on the abutment teeth by micropreparations in
the enamel

The metal surface is coated with silicate and silane to bond the resin adhesive to the adhesive
anchor. The enamel should be conditioned using conventional techniques.



                                                                                Mostafa Fayad 10
                                                                            Attachments in RPD


   C ) Radicular / intraradicular stud type

        - Stud precision attachments are primarily used on roots and implants for retaining
        removable partial dentures or over dentures. All stud attachments MUST be
        parallel to each other to provide ease of insertion and removal and reduce wear
        potential.

        - Do not engage labial soft tissue undercuts with the denture base flange, as this
        will alter the path of insertion and cause excessive wear and servicing
        requirements.

        - Stud attachments are low in profile to reduce leverage upon the retaining
        abutments, are easy for patient hygiene maintenance, allow physiologic
        independent movement of abutments, and are easy to service

        advantages :-

           - that they promote better oral hygiene .

           -the crown root ratio is also enhanced with the low profile of the stud type
           attachment

        indication :-

           1 – used with remaining root or v. short crown

           2 – used with over denture

           Types

           A ) Extra radicular type

                1 ) Dalbo a   achment-:

                   - the patrix is attached to remaining root

                   -the matrix got fingers that are protected using a Teflon ring

                   -Teflon ring provide compressibility during function

                   - A new over denture attachment system that allows the user to replace
                    both the male (threaded sphere) and female. The females engage the
                    undercuts of the sphere to allow for superior retention and less wear on
                    the height of contour.


                                                                              Mostafa Fayad 11
                                                                   Attachments in RPD


       - Components are less than 4mm in ver        calheight.

       - types :- - resilient type ( fabricated with spacer ) , -non- resilient type(no
        spacer used)

    2 ) Ceka stud attachment :-

    The patrix has attached to remining root

    - patrix has asplit to increase the friction

    - -types :- -resilient type - non resilient type

    - The new Ceka Revax (M2):-

     is the smallest fully adjustable and serviceable stud attachment system.
    This adjustable spring pin attachment may be utilized as a traditional stud
    (with cast copings), or inverted as an intraradicular connector for over
    dentures or removable partial dentures on roots and implants.

    - It may be used for a resilient or tissue born prosthesis, or for a
    combination abutment and tissue supported prosthesis. The small size
    allows for usage when space is at a premium--ideal for ‘close bite’
    situations. Clinical, laboratory, and servicing are routine procedures that are
    adaptable to the individual’s needs and/or techniques. Space requirements
    for the Revax (M2) are 3.8mm in height, and 3.4mm in diameter.

    - Tradi   onal Ceka Axial (M3)

    The tradi onal Ceka Axial has been in use for over 30 years. As a result, it is
    one of the most widely used attachments in the world. It is much like the
    Ceka Revax Axial, but for one major difference--the Ceka requires 0.45 mm
    more ver cal clearance. When space is available, select the tradi onal M3
    Ceka as it is stronger and easier to service.

B ) intra radicular type

    1 ) Zest anchor

     Zest concepts: lowering the fulcrum (force
application), the intradicular female (inside root), and the
easy replacement of the male.

    - Advancements allow the male to freely rotate and

                                                                     Mostafa Fayad 12
                                                                            Attachments in RPD


           move within the housing or denture cap

               - the wide band on the male allows for increased retention and reduced
           wear (less bending and breakage), the female has a titanium coating for
           hardness and a smoother internal surface

               The males may be placed "chairside." The female may be used with a cast
           coping or directly placed into a root. -There are two sizes--regular (4.0 mm
           height, 3.8 mm width) and mini (2.3 mm height, 3.3 mm width)



   D )Bar type

    indication:-

        1 - overdentures, to connect between 2 roots

        2 - removable par       al dentures to connect between 2 teeth

        3 - implant prosthesis

        4 – in case in presence of few teeth or long edentulous area

        - Bars may be rigid or resilient, permitting free movement of the prosthesis to
        direct forces away from the retaining abutments to the supportive bone and tissue.

    The shape of the bar is indicated by

    the amount of room available.

    the shape of the alveolar ridge.

    the type of construction.

          the round plasti-wax bar, more easily bent to follow the alveolar crest. Do not
        engage labial soft tissue undercuts with the denture base flange, as this will alter
        the path of insertion and cause excessive wear and servicing requirements.



    Bar systems are generally in one of three types:

            1. Prefabricated ‘Dolder’ type



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                                                             Attachments in RPD


                    Dolbar bar unit                   Dolbar bar joint

               rectangular cross section            oval in cross section

                             Rigid                        resilient

             strong (Ceramic) abutment                weak abutment




                                      Regular            Mini

2. Plastic ‘Ackermann &Hader’ type

                  Ackermann                               Hader

              oval in cross section                   Key hole shape



   used in curved arch as can follow the ridge curvature & be used in anterior
   maxilla the matrix is the bar & the patrix is the sleeve

   * Hader attachment:- the most popular of all bar systems due to its
   economy and simplicity.

    *advantage :-

   1 - superior stability,

   2 –retention

   3 - abutment splinting                                             Ackermann
   Clips



3. Round ‘Clip" bars and riders



                                                                Mostafa Fayad 14
                                                                              Attachments in RPD


A round bar is useful in situations where the bar must be bent to accommodate the ridge
anatomy, or in close-bit situations.




                    Round Bar



        E) Magnet



        F) Locator Root

                    The Self-Aligning feature of the LOCATOR attachment allows a patient to
                    easily seat their overdenture without the need for accurate alignment of the
                    attachment components.

                    o Long Lasting--good for 110,000 inser     on cycles!

                    o Self-Aligning--patient can bit prosthesis to place!

                    o Patented Dual Retention

                    o Unique Pivoting Denture Cap

                    o Choice of Retention--5, 4, 3, and 1.5 lbs

                    o Extra-Radicular Design

      G ) Auxillary attachment

             - they include component such as plunger , hingers & screws these types of
             attachment must be incorporated into the design of the prosthesis

             *types:-

             1) plungers

             2 ) screw units

                    -used in Fixed removable partial denture

                                                                                Mostafa Fayad 15
                                                                   Attachments in RPD


      -the anterior part of denture is fpd & posterior part is screwed to it

3 ) hinged flanges ( swing lock p .d ) :-

    -labial flange is connected from one side by a joint & a lock on other side

    - used with R.p.d where labial under cut is found

    -so in much R.p.d , labial undercut & teeth interdental area are used to
    increase retention

    - Usually made of co /cr to splint weak abutment

    indication & adv of swing lock p .d :-

    1 – Splinting of weak abutment 2 –unfavorable tooth contour

    3 – Unfavorable so        ssue contour       4
                                                 – for maxilla facial cases

    5 – for arch with expected further extraction

    Contraindication:-

    1 – shallow labial vestibule             2 – expensive

    3 – un co-opertive patient               4 –where esthetic are needed

4) Distal Stress Equalizers (DSE)

 - The DSE Hinge is intended for use on bilateral clasp
retained free end removable partial dentures to reduce
loading or torquing of abutments. The small size is easy to
work with and eliminates multiple inventory requirements.
The unique design provides for easy freeing after casting
and provides total lateral stability.

 - For patients, it allows patient comfort and abutment protection by allowing
independent unilateral function eliminating torquing leverage on the abutments
on the nonfunctioning side. The miniaturized size allows utilization in short vertical
spaces and provides for good esthetics.

5) Telescopic prosthesis with isoclip attachment or spring loaded plunger.

6) Sectional denture prosthesis with Mechanical locking -PW Bolt or Frictional
resistance PW split post.

                                                                      Mostafa Fayad 16
                                                                            Attachments in RPD




    Overview attachments used in :-

    A ) R.P.D : -

    1 ) extracoronal a       achment       2 ) intracoronal a       achment

    3 )bar a       achment                 4 ) auxillary a     achment

    B )partial over denture :-

    1 ) stud a      achment                 2 ) bar a   achment

    c ) implant supported partial denture :-

    1 ) extracoronal a       achment       2 ) stud a   achment

    3 ) screw on

 Treatment planning
     A) Intra oral assessment

    intra oral examination should include assessment of the soft & hard tissues.

    The teeth should be assessed for :-

    a – caries                                               d– mobility & angulation

    b – vitality                                             e- clinical crown length

    c – bone support                                         f- crown root ratio

    A thorough periodontal , occlusal & radiographic examination is also required to
    complete intra oral assessment


    periodontal examination :-

           a full periodontal assessment should be carried out this should include full
           arch pocket charting , an assessment of oral hygiene status & a full
           radiographic assessment of bone support as fixed or removable prosthesis
           may influence the pattern of health & disease of periodontium .



                                                                              Mostafa Fayad 17
                                                                    Attachments in RPD


pre - prosthetics treatment :-
         Hard &soft tissue problems such as : -
               A – poor gingival contour
               b – soft tissue hyperplasia
               C – in adequate crown length
                d – bonitori & high frenal attachment
         After initial pdl therapy has been completed any surgical treatment should be
         carried out next
   prosthetic consideration :-
              - the possible design features with regard to retainers & fram work
         design should always be thought by the dentist & technician with both the
         surveyed diagnostic casts mounted on an articulator & patient present
              - the selection of abutment teeth is influenced by 3 factors :-
         1 – the number & distribution of the remaining teeth
         2 – adequacy of p d l support
         3 – analysis of occlusion




                                                                      Mostafa Fayad 18
                                                                            Stress breaker


                                       Stress breaker

     It is a device, which allows movement between the denture base and the retainer
to reduce lateral and tipping forces on abutment teeth. It is also called "Stress
director" or "Stress equalizer".

     The term articulated prosthesis is applied to a broken-stress partial denture.


      Strain on the abutment teeth is minimized through:
      1. Broad tissue coverage,
      2. The use of functional basing.
      3. Use of narrow teeth and harmonious occlusion.
      4. Placing the artificial teeth on the anterior two-thirds of the base.
      5. Correct choice of direct retainer. Using a flexible clasp causes less
          transmission of torque due to the release of stresses which occur when the
          clasp tends to deform. This principle is fulfilled by stress breakers.


Indications:
   1- When internal attachments are used.
   2- In distal extension removable partial dentures to distribute the load between the
      abutment teeth and the ridge.
   3- In cases exhibiting weak abutment teeth and well formed ridges.
Advantages:
   1- Decrease horizontal forces acting on the abutment teeth thus it preserve alveolar
      support of these teeth
   2- Distribute the stress between the abutment teeth and the residual ridge.
   3- Prevent the quick damage of abutment teeth if relining is needed but not done.
   4- Providing physiological stimulation of bone which prevent bone resorption.
Disadvantages:
   1- Difficult to construct and expensive.
   2- Concentration of vertical and horizontal forces on the ridge may increase ridge
      resorption.

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                                                                            Stress breaker


   3- If relining is not done when needed it will leads to the increase of ridge
      resorption.
   4- Less tolerated by the patient.
   5- Flexible connectors may be bent and distorted.
   6- Some split connectors pinch the underlying soft tissue or tongue as they open
      and close under function.
   7- The effectiveness of indirect retainers is reduced or eliminated.
   8- Repair and maintenance of any stress breaker is difficult.
   9- All mechanical devices that are free to move in the mouth may collect debris
      and become unclean.


Types of stress breakers:
        Type I - Those utilising a hinge or moveable joint.
        Type 2 - Those utilising flexible connection


   1- Type 1 Stress-breakers : Those having a movable joint between the direct
retainers and the denture base.
      This joint may be in the form of hinges, sleeves and cylinders or ball and socket
   devices. They are necessary when internal attachment is used , but can also be used
   with clasp.
      The joint allows vertical and hinge movement of the base to prevent direct
   transmission of tipping forces to the abutment. Dalbo extra-coronal retainer and
   Chrisman intra-coronal retainer are examples of this group.


2- Type 2 Stress-breakers : Those having a flexible connection between the direct
retainer and the denture base. (The articulator partial denture design) These include :


a- Wrought wire connectors:
      Double lingual bars of wrought metals, one supporting the
clasps of other components and the other supporting and connecting
the distal extension bases. They may be united at midline by soldering.


                                                                          Mostafa Fayad 2
                                                                               Stress breaker




Torsion bars
These may be used in the design of a lower partial denture
carrying bi-lateral free-end saddles. Bars extend anteriorly
from the clasp units on each side to join a lingual bar near
the mid line. Flexibility can be controlled by varying the
cross-section of the torsion bars, the method of construction (cast or wrought) and the
material of construction (normally gold alloys or cobaltchromium alloys).
       Disadvantages are associated with the use of the torsion bar structure in that the
double bar system is liable to trap food and cause irritation to the tongue.


b- Split major connectors: (used with long saddle)
       This includes split bar major connector and split plate
major connector. The major connector is split into two portions,
upper rigid part which carries the clasp units, and lower slightly
flexible part which attached to the saddle.
       Forces applied to the base pass anteriorly along the lower
bar and then along the more rigid upper bar reaching the abutment. Tipping forces are
thus dissipated by the flexibility of the lower bar and through the distance traveled.

   -   Split casting modifying the lingual plate: a split of appropriate length is made at
       the inferior border of the plate. The saddle is joined to the more flexible part of
       the plate. The lower part must be flexible in the vertical direction, than
       horizontal direction, so that the appliance will have lateral rigidity to distribute
       horizontal force widely. This design applied in long class II cases.

   Disadvantages: The slit opens slightly in function and theoretically is liable to trap
either the tongue or food particles. With a long saddle, however, the slit is anteriorly
placed and in this position may be intolerable to some patients. The patient using
dental floss can clean the slit easily.




                                                                          Mostafa Fayad 3
                                                                           Stress breaker


c- Mesial placement of occlusal rests
This offers the simplest available approach to stress-breaking. The degree of stress-
breaking achieved is, though, much less than that available where more complex
devices are employed. It may be used in the design of either upper or lower dentures.
By positioning the rest of the clasp unit on the mesial instead of on the distal fossa of
the abutment tooth and by using a minor connector to link the rest to a major
connector (for example, a lingual bar) some flexibility may be introduced into the
clasp unit/saddle link




   -   The use of semi-flexible bar: (used with short saddle)

           This is more applicable with short saddles, it involves mesial placement of
   an occlusal rest. The occlusal rest is placed on the far zone of the abutment tooth.
   The abutment is rigidly clasped, and joined to the clasp onto the opposite dentulous
   side by a rigid connector (lingual bar). The saddle is joined to the retainer unite by
   a semi-flexible bar that allows some movement and provides stress breaking action.
   An embrasure clasp is usually used on the dentulous side.

   - A lingual bar connector with a flexible distal extension:

   The lingual bar connector used to join two saddle is distally extended on each side
   and then recurved along the residual ridge to allow attachment into the matrix resin
   of the saddle. The support is design on mesial aspect of the abutment to increase
   the length of the bar and better distribute the load.




                                                                         Mostafa Fayad 4
                                                                    Stress breaker


d- Clasps having stress breaking action:
1. Gingivally approaching resilient I-bar clasp.

2. Occlusally approaching clasp having resilient retentive wrought gold wire arm
(Combination clasp).

3. Back-action clasp.

4. Reverse back-action clasp.

5. Extended-arm clasp.

6. Ring clasp.

7. Wrought wire clasp.

8. RPI clasp.

9. RPA clasp.




                                                                 Mostafa Fayad 5
                               ARTIFICIAL TEETH

     Selection of artificial teeth for form• colour and material is made easy by the

presence of natural teeth.

FUNCTIONS:

     1. Cutting, chewing and grinding of food.

     2. Restoration of esthetics.

     3. Functional performance as speech.

     4. Maintaining both the horizontal and vertical occlusal relations and
       maintaining the proper temporo-mandibular joint function.

     5. Preserving the remaining oral structures by preventing over-eruption
       and drifting of the remaining natural teeth


DESIRABLE CHARACTERISTICS


     1. Have the color(shade), translucency, size, shape, and characterization
     similar to the natural teeth they replace.
     2. Be easily shaped with conventional dental burs.
     3. Be easily characterized with conventional dental stains.
     4. Have a hardness and abrasion resistance similar to the opposing enamel or
     dental material.
     5. Chemically bond to the denture base material or RPD alloy to which they
     are attached.
     6. Be resistant to staining by oral fluids and microorganisms
     7. Be chemically inert.
     8. Be odorless and tasteless and not pick up odors or tastes from oral fluids.
     9. Have a surface which is dense to avoid harboring oral fluids and
     microorganisms.
     10. Be capable of being cleaned by customary oral hygiene technics and
     materials.
     11. Be of low initial cost and inexpensively repaired or replaced.
     12. Be capable of being repaired and replaced by customary dental technics
     and materials.
     13. Be strong enough to resist the forces which will be applied.
     14. Not soften or warp in hot water or conventional denture cleansing
     solutions.
Bonding between the teeth and the denture base
1- Mechanically
2 - Chemically
3 - Chemomecanical
4 - Acid etching microretention
5 - Silnation (tribo-chemical method): combination of chemical bonding and acid
etching

Types of tooth replacements

    Artificial teeth may be attached to denture bases in one of the following
          manners

  1) COMMERCIALLY AVAILABLE DENTURE TEETH:

             Acrylic resin or porcelain teeth attached to denture bases by an
          intermediate layer of acrylic resin. Mechanical attachment in the denture
          base may be accomplished by loops, mesh or nail heads retention.
a- Porcelain teeth are mechanically retained to the denture bases. The
     posterior porcelain teeth are attached by acrylic resin in their
     diatoric holes, while the anterior teeth are attached by acrylic resin
     around retentive pins located on the lingual surfaces of teeth.

b- Acrylic resin teeth are retained by chemical union with the acrylic
  resin covering metallic denture bases during laboratory processing
  procedures.

c- Reinforced acrylic pontics (RAP): RAP is made of modern cross-
linked copolymers. It is a solid, hard plastic which provides good
esthetics and shade control and provide better attachment to the metal
base compared to cementation.
d- Metal reinforced denture teeth
  They are prosthetic teeth constructed from denture teeth. The facial
portion of a denture tooth attached to the framework with a tooth-
colored resin. Retentive loops,beads, or posts are used to mechanically
attach the tooth to the framework. The tooth may also be adhesively
bonded to the framework
e- Acrylic resin teeth with amalgam stops
  This type of teeth is used to slow and control the occlusal wear when
the acrylic teeth is opposite by porcelain or natural teeth as in case of
single denture. The amalgam stops can be inserted when the teeth are
balanced on the articulator before delivery to the patient, or they can be
inserted after a period of patient use so the individual wear pattern of a
generated occlusion is apparent.
f- Acrylic resin teeth with gold occlusal surfaces
             Gold occlusal surfaces are considered the best material to oppose
          natural teeth as in case of single denture.
             One or more occlusal surfaces on each side of the denture can be
          casted in gold to stop the abrasion of the acrylic teeth and protect the
          opposite teeth from abrasion. This type of teeth is impractical for most
          patients because it is expensive and takes more time for fabrication.
          g- IPN resin
             This material consists of an unfilled, highly cross-linked, inter-
          penetrating polymer network. The wear resistance of this material is
          higher than that




             A                                                c




                          b



              Mechanical means of attachment of teeth to metal base.


INDICATIONS:
1. When a processed plastic base will be used to attach the prosthetic teeth to the
framework.


CONTRAINDICATIONS:
1. Where there is insufficient space occlusal/incisalgingival or mesiodistally for a
denture tooth-plastic base combination.
a) Less than 5 mm between the occlusal plane and the edentulous ridge.
b) Single tooth edentulous space.
2. Where protrusive or lateral occlusal guidance will be on the prosthetic teeth.
3. When available denture teeth do not satisfy esthetic or occlusal requirements. In
these situations a custom made prosthetic tooth is necessary.


ADVANTAGES:
1. Denture teeth are prefabricated by several manufactures.
2. There is a large selection of shades, sizes, and shapes. An acceptable denture
tooth can
usually be found.
3. Available in plastic and porcelain.
4. Can be easily adjusted (particularly plastic) to fit the framework, available
space, existing occlusion, and desired size and shape of the tooth.
5. There is great flexibility of arrangement of denture teeth.
6. The denture tooth arrangement can be tried in the patient's mouth to preview the
esthetics of the completed denture.
7. Replacement of denture teeth on a processed plastic base is fairly easy and rather
inexpensive.


DISADVANTAGES:
1. Plastic and porcelain denture teeth may fracture where as metal prosthetic teeth
will not.
2. Plastic denture teeth are not as abrasion resistant as metal prosthetic teeth.
3. Cannot be used in small spaces, or where occlusal guidance will be on
  2) PROCESSED PLASTIC TEETH


Processed plastic teeth are custom made prosthetic teeth processed from tooth
colored heat polymerized acrylic resin. They are attached to the framework by
retentive mesh, loops, beads, or posts. They may be used with or without a
processed plastic base.


INDICATIONS:
1. A posterior edentulous space which is too small occlusal/incisal- cervically or
mesiodistally for a denture tooth.
2. Where available denture teeth do not satisfy the esthetic or size requirements.


CONTRAINDICATIONS:
1. Where a simpler prosthetic tooth-denture base combination may be used.
2. As anterior prosthetic teeth (custom facings are used because of superior
esthetics).


ADVANTAGES:
1. Can be utilized in very small spaces.


DISADVANTAGES:
1. Difficult to obtain esthetic shade match with processed plastic teeth.
2. Processed plastic teeth abrade more than commercial available denture teeth.
3. A wax try-in is not possible.
3)      ACRYLIC         RESIN       OR   PORCELAIN      FACINGS       (STEEL’S
        BACKING):

           a- Readymade facings
           Facings      used       on    RPDs   are
     manufactured prosthetic teeth consisting of
     two parts: a veneer of tooth colored porcelain
     or plastic (the FACING) and a BACKING
     made of a plastic material.
           The backing is incorporated into the
     wax-up of the framework. The facing and
     backing are related by a slot and groove. The
     facing is cemented onto the framework with a
     dental adhesive.
           Because of their many disadvantages and the advent of custom made
     facings using light-cured composite resin materials, the use of commercially
     purchased facings is being phased out of RPD prosthodontics.


           b- custom made facings

           Acrylic resin or porcelain facings are cemented to metal backings.
     The metal backing forms the lingual half of the tooth and is an extension
     from the partial denture framework. Tooth replacements in the form of
     facings are fabricated by the laboratory and cemented by the dentist at the
     time of denture insertion.

           This causes difficulty in obtaining satisfactory occlusion and lack of
     providing adequate contours, adding to the unesthetic display of metal at
     gingival margin.
             A modification of this method is the attachment of ready-made acrylic
      resin teeth to the metal base with acrylic resin of the same shade. This is
      called pressing on a resin tooth and is not the same as using acrylic resin
      for cementation. It is particularly applicable to anterior replacements, since it
      is desirable to know in advance of making the casting that the shade and
      contours of the selected tooth will be acceptable. After a labial index of the
      position of the teeth is made, the lingual portion of the tooth may be cut
      away or a posthole prepared in the tooth for retention on the casting.
      Subsequently the tooth is attached to the denture with acrylic resin of the
      same shade. Because this is done under pressure, the acrylic resin attachment



DISADVANTAGES:
1. Not as esthetic as denture teeth because the backing shows through the veneer.
2. A wax try-in is difficult.
3. If occlusion is placed on the backing the refractory cast must be mounted on an
articulator so the occlusion can be developed in the wax pattern for the framework.
4. Limited selection of sizes, shapes, and shades.
5. Selection more difficult than for denture teeth because there is no mold guide.
Selection is made from mold chart with sizes indicated.
6. More difficult to obtain than denture teeth.
7. Subject to fracture (particularly porcelain).


                                                   Steel’s Backing
  4) Tube teeth

                Acrylic resin or porcelain tube teeth are prepared by drilling a channel
        from the base of the tooth upward to form a tube. A metal post casted with
        the partial denture framework is specially designed for the attachment of the
        tube teeth. The tube teeth is fixed to the post by cement.

                Tube teeth are usually used as single tooth replacements, where a
        maximum of three teeth are used.


INDICATIONS:
1. Single tooth edentulous spaces which preclude the use of a processed plastic
base.
2. Short (occlusal/incisal cervical) edentulous spaces in conjunction with a metal
base. The tube tooth will be cemented to the post, not attached by a processed
plastic base.
Anterior tube teeth are usually butted to the edentulous ridge; posterior tube teeth
usually have metal facial and lingual finish lines


CONTRAINDICATIONS:
1. Where a denture tooth processed plastic base may be used.
2. Where the occlusion must be on metal.
3. Where the space is too narrow or too short for a denture tooth. A metal pontic,
custom made facing, or processed plastic tooth is used in these situations.


DISADVANTAGES:
1. Subject to fracture.
2. No wax try-in possible to preview the esthetics of the completed denture.
3. No chemical bond between the tube tooth and the framework. The 4-Meta luting
cements show promise when bonding denture teeth to the metal framework.




             A tube tooth. A metal post casted with the partial denture framework specially designed for
             the attachment of the tube teeth.

   5) Braided post
        It is similar to tube teeth , both forms depend on a centrally located reinforcement strut , however
the method used for strut configuration re significantly different .

        A braided post is created by twished two small diameter wax ropes around one another in a helical
fashion the frame work then casted . the acrylic resin tooth is attacted to the frame work using heat or self
cure acrylic resin

   6) Metal teeth

                     Metal teeth are usually used as replacements of posterior teeth where
           space is limited for the attachment of an artificial tooth. Second molars
           may be replaced as part of partial denture casting as a space filler to
           prevent migration of an opposing second molar. The metal teeth are
           esthetically unsatisfactory, difficult to attain any occlusal adjustment and
           are abrasion resistant; hence occlusal contact should be held to a
           minimum to avoid damage to the periodontium of the opposing teeth.
                      Metal teeth• self cleansing pontic.



Metal teeth with acrylic window

       In cases of reduced space and esthetic requirement the buccal surface
  of the pontic is removed and tooth couloured acrylic is packed into the
  buccal surface

 * Replacements with chemical bonding

    Recent developments provide means of direct chemical bonding of
    acrylic resin to metal frameworks without using loops, mesh or
    mechanical locks.

    1- Sections of a metal framework that are to support replacement teeth
    can be roughened with abrasives and then treated with a vaporized silica
    coating. On this surface an acrylic resin bonding agent is applied,
    followed by a thin film of acrylic resin to act as a substrate for later
    attachment of replacement acrylic resin teeth or for processing of the
    acrylic resin tissue replacements.

    2- A second method of fusing a microscopic layer of ceramic to the
    metal is accomplished by a process referred to as tribochemical coating.
    This system involves sandblasting the metal framework with a special
          silica particle material, Rocatec-Plus. Silica from these particles is at-
          tached to the framework by impact. A silane is added to this ceramic-like
          film to form a chemical bond between the silicate layer and the denture
          base acrylic resin.

           3- Denture base acrylic resins formulated with 4-Meta are also available
          and provide a mechanism of bonding acrylic resin to metal.




INDICATIONS:
1. A posterior edentulous space which is extremely small mesiodistally or
occlusocervically.


CONTRAINDICATIONS:
1. Anterior edentulous spaces.
2. Where a simpler or more esthetic type prosthetic tooth may be used.


ADVANTAGES:
1. Can be used where other prosthetic teeth can not.
2. Have all the advantages of cast metal such as permanence of form, wear
resistance, dense surface, etc.


DISADVANTAGES:
1. Not as esthetics as other types of prosthetic teeth even when veneered with tooth
colored plastic.
2. All the disadvantages of metal such as hardness, wear of opposing teeth and
tooth materials, etc.
3. May require that the refractory cast be mounted in an articulator to develop the
occlusion of the pontic.

4. No wax try-in possible.




                      Acrylic Resin Versus Porcelain Teeth



PORCELAIN DENTURE TEETH


Porcelain denture teeth have the following advantages in comparison to
plastic denture teeth:
1. More esthetic.
2. More dense surface which is hard, abrasive, resistant, less prone to stains and
easier to clean.


Porcelain denture teeth have the following disadvantages in comparison to
plastic denture teeth:
1. Harder therefore transmit more force.
2. More abrasive, particularly when the glaze is broken. Should be used opposing
porcelain surfaces only.
3. More brittle. More apt to crack, chip and fracture.
4. Adjusting (grinding) to fit the framework and opposing occlusion is more
difficult.
5. Do not chemically bond with plastic.
         Must be mechanically attached to the denture base. The retentive pins and
diatorics limit the amount of tooth modification which can be done. The tooth-base
interface will eventually stain because of the ingress of bacteria and fluids into the
space.
6. An objectionable "clacking" noise may be heard when porcelain teeth occlude
with enamel, cast metal or porcelain surfaces of opposing teeth.


PLASTIC DENTURE TEETH


Plastic denture teeth have the following advantages in comparison to
porcelain denture teeth:
1. Easier to adjust to fit the framework, space limitations and existing occlusion.
2. Chemically bond with plastic making a one piece denture tooth-plastic base
combination.
3. Softer so forces are dampened.
4. Will not abrade opposing enamel, amalgam, or cast metal restorations.
5. Can be restored with cast metal occlusal surfaces and amalgam restorations.
6. Less noise from tooth contact.
7. Can be custom “stained” to match the color and characterization of the natural
teeth.


Plastic denture teeth have the following disadvantages in comparison to
porcelain denture teeth:
1. Less hard. Will have more occlusal wear and may be abraded by brushing with
an abrasive cleaner.
2. Less esthetic.
3. Surface is more porous and will stain easier.
4. More difficult to remove wax from tooth during the wax-up of the denture.
5. More difficult to finish and polish denture.




THE CHOICE OF PORCELAIN OR PLASTIC DENTURE TEETH
       Plastic denture teeth are used on RPDs almost exclusively because the
available space precludes the use of porcelain denture teeth. The esthetics of plastic
denture teeth is acceptable and their advantages far outweigh their disadvantages.
The Portrait IPN teeth by Dentsply have greatly improved esthetic characteristics.

               Acrylic Teeth                                Porcelain Teeth

 - Have strong chemical bond with             -Less efficient mechanical bonding with
 denture bases.                               denture bases.

                                                  Tendency to fracture specially in
 - Tough, having good resistance to          patients having heavy biting force.
 breakage hence are used in closed bite
 cases and narrow space.                       - Require adequate space to ensure strong
                                              bonding.

 - Resilient, causing less trauma to
                                              - Hard.
 residual ridges.

                                              - Chip during grinding. Excessive grinding
 Can be altered by grinding to fit limited
                                              may alter the diatoric holes and causes
inter-ridge space.
                                              difficulty to restore the highly polished surface.

 - Light in weight.                           - Heavy weight.

 - Have tendency to stain and change in
                                              - Resist staining.
 colour.

 - Have tendency to excessive wear, thus
                                              - Resist wear and maintain occlusal vertical
 affecting both vertical and horizontal
                                              dimension.
 occlusal relations.

 - Rebasing dentures is not easily done ,     - Teeth can be easily separated facilitating
 as it is difficult to remove teeth.          rebasing procedures.
 - Can be used opposing gold
 restorations as they cause minimum       - Cause wear in opposing gold restorations.
 amount of wear.

                                          - Clicking sounds



Selection of prosthetic teeth


             A)        SELECTION OF ANTERIOR TEETH


 1- Color (shade) of the teeth selection

      - The selection of a suitable color for the teeth is a simple procedure by
   using a shade guide. For single or partial denture the shade must be
   harmonized with the remaining natural teeth.

      - The artificial teeth should be moistened before marching it with a shade
   guide.

      - Natural light is better than artificial light.

      - Avoid fatigue by providing intermittent rest to the eyes.

2- MOULD SELECTION

- The artificial teeth should be in harmony with the facial feature and natural
teeth.

- Space regaining measurements (e.g. proximal slicing or crown fabrication) are
considered when the edentulous apace is decreased due to migration of natural
teeth.

3- Selection of material for anterior teeth
1-      Acrylic denture tooth

2-      Porcelain denture tooth

3-      Inter changeable facing

4-      Tube teeth

5-      Pressed on / post



              B ] Selection of posterior teeth

1- The selection of the proper tooth-size or mold is based on:
   - The capacity of the ridge to receive and resist the forces of mastication.

     - The space available for the teeth.

     - The esthetic requirements.

2- Shade

      The shade of the posterior teeth should be in harmony with the shade of
the natural teeth. The maxillary bicuspids may be slightly lighter than the other
posterior teeth but not lighter than the anteriors.

3- Occlusal form

The ridge form can be used as an index for the amount of cusps angulation. The
ridge form can be used as an index for the amount of cusp modification.

The available three major groups of occlusal forms are:

- Anatomic teeth of 30, 33 degrees cusps or more.

- Semi-anatomic teeth of 20 degrees cusps.

- Non-anatomic of 0 degree, cuspless teeth (flat teeth).
The anatomic teeth give greater efficiency and bilateral balance. They are
commonly used for patients having normal ridge relations and well- developed
ridges.

Advantages of non-anatomic teeth

1- They are more adaptable to universal jaw relations and class II and class III
jaw relationships.

2-     They are more easily used in cross-bite situations.

3-     They permit long centric freedom.

4-    They give the patient a sense of freedom as they do not lock the mandible in
one position only.

5-     They eliminate horizontal forces that may be more damaging than vertical
forces (less bone resorption).

6-     No need for adjustable articulator and setting is easier.

7-    Balance can be obtained through balances ramp, compensating curve or
pleasure curve.

The non-anatomic teeth offer less masticatory efficiency. However, they may be
used in the following cases:

- Cross-bite relationship.

- Flat ridge.

- Knife-edge ridges.

- Patients with T.M.J problem or neuromuscular in-coordination.

- Large inter-ridge space.

- Milling type of chewing pattern.
4- Selection of material for artificial teeth
     Artificial teeth may be:

1-      Acrylic denture tooth

           - Acrylic resin teeth with amalgam stops.

           - Acrylic resin teeth with gold occlusal surface

           - IPN resin.

     2- Porcelain denture tooth

     3- Tube teeth

     4- Metal tooth

     5- Pressed on acrylic

     6- Braided post

Factors Influencing the Selection of Posterior Teeth

The selection of the size and form of posterior teeth is influenced by

1)    The size and form of the remaining natural teeth which acts as a guide for
tooth selection.

2) The cusp height of the remaining natural teeth which determines whether to
use cusped or non cusped teeth.

3)   The condylar inclination A steep condylar inclination requires the use of
cusped posterior teeth.

4)    The condition of the remaining residual ridge, where a flat ridge
necessitates the use of flat (cuspless) teeth.

5)     The amount of available space determines the size of the replacement
teeth.

6)      Type of tooth material present in any restoration in the mouth.
                                                                 DENTAL SURVEYOR


                     THE DENTAL SURVEYOR
       Surveying is the procedure of locating and delineating the contour and
position of the abutment teeth and associated structures before designing a
removable partial denture. The instrument utilized for surveying is termed the
dental surveyor .

       The dental surveyor is an instrument used to survey the abutment teeth
and associated structures.

The survey line

       The survey line or the height of contour is a line encircling a tooth
designating its greatest circumference at a selected position determined by the
dental surveyor. The area of the tooth above this line is non-undercut area and
the area below is the undercut area.

        Undercut: An undercut is formed when the base of an object is smaller
than its top. Undercut on abutment teeth is a dig or a burrow lie below the height
of contour.

       The primary purpose of surveying is to plan the design necessary to
fabricate a removable partial denture which can be easily inserted in the mouth
and retained in place during function.

      Dr. A. J. Fortunati was the first to demonstrate the advantages of using a
mechanical device to map the contours of the abutment teeth. At a 1918 clinic in
Boston, Fortunati replaced the steel analyzing rod of a “Bridge Parallelometer”
with a graphite rod, then accurately traced survey lines of the greatest
convexities of the teeth.

       Around 1920, Dr. Chayes developed the Parallelometer. This instrument
could be used both intraorally and at the laboratory bench to ensure parallelism
of precision attachments. The instrument also could be used to identify non-
parallel and/or undercut surfaces of prepared teeth.

Types of dental surveyors
       There are two types of dental surveyors: electronic and mechanical. The
electronic surveyors are complicated and expensive and their use is restricted to
research and large commercial dental laboratories.

      The original Ney surveyor was introduced in 1923

       A recently designed surveyor dramatically exposes undercut areas by
projecting a beam of laser light. Some of these modifications are applied to the


                                                               Mostafa Fayad - 1 -
                                                                     DENTAL SURVEYOR


 newly developed surveyors which have been already introduced to the dental
 market be feb.2008 and of these trends:

        *The Da Vinci is distinguishes by its dual, multi-jointed arm design,
 allowing the user to effortlessly switch between the primary milling, drilling arm
 and the secondary tapping, surveying arm.

        Microsurveyor Compass (Denstply Sankinkk, Tokyo,
 Japan) from Japan is a small hand-held surveyor. It establishes
 the path of insertion by tilting its vertical arm rather than its
 cast holder.

        Micro analyzer: it is a surveying instrument for measuring the amount of
 under cut electronically.

        Stress –o- graph : it is type of surveyor with two vertical tool holder.



 Parts of the dental surveyor
 The principal parts of the Ney surveyor are as follows:

1.      Horizontal Platform on which the base is moved.

2.      Base equipped with a lock screw, on which the table swivels by ball and
  socket joint, permits movements of the table in all directions.

3.        Survey Table (cast holder): to which the cast is attached، it is equipped
  with a clamp to lock the cast in place‫ ؛‬the table can be tilted in any horizontal
  plane to help in analyzing the model in relation to vertical plane. The surveying
  table consists of a top and a base joined together by a ball and socket joint which
  permits tilting of the top in any direction. A lower locking device is used to fix
  the tilt of the top part. The top of the table is equipped with a clamp to lock the
  cast in place.

4.      Vertical arm that supports the superstructures.

5.      Horizontal arm with spindle housing and a tightening screw, from which
  the surveying tool suspends.

6.      A surveying arm (spindle): It drops from the horizontal arm and
  moves vertically at right angles to the base. It can be fixed at the desired
  height by a locking device. The lower end of the spindle arm contains a tool
  holder and a tightening screw to fix the tool.

7.      Paralleling Surveying tools that will be used for surveying:


                                                                   Mostafa Fayad - 2 -
                                                                            DENTAL SURVEYOR


A- Analyzing rod: is a rigid metal rod used for diagnostic purposes in the
selection of the path of placement.

B-Carbon marker: is used for the actual marking of the survey lines on the cast.
A metal shield is used to protect it from breakage.

C- Undercut gauges: are used to measure the extent of the horizontal undercuts
that are being used for clasp retention. Usually there are three sizes: 0.01، 0.02
and 0.03 of an inch.

D- Wax trimmer is used to trim excess wax that may be inserted into those
undercut areas, which are to be obliterated.

E- Reinforcing sheath : It is a metal sheath (usually half round) used to
maintain the carbon marker from breakage.




Ney dental surveyor               Jelenko (Wills) surveyor               Williams surveyor



Parts of the dental surveyor: 1.Horizontal Platform، 2.Vertical arm، 3. Horizontal arm، 4. Table
with clamp، 5. Base، 6. Mandrel (spindle)، 7. Storage compartment for storing the tools، 8.
Tightening screw، 9. Screw to lock spindle, 10. locking screw for tilt top, 11,Rack for
accessories.



        The most widely used dental surveyors are the Ney and the Jelenko , they
differ principally in

1- In Jelenko surveyor: by loosening the nut at the top of the vertical arm, the
horizontal arm may be made to swivel. The objective of this feature, originally

                                                                          Mostafa Fayad - 3 -
                                                                   DENTAL SURVEYOR


designed by Dr. Noble Wills, is to permit freedom of movement of the arm in a
horizontal plane rather than to depend entirely on the horizontal movement of
the cast.

To some this is confusing because two horizontal movements must thus be
coordinated. For those who prefer to move the cast only in a horizontal
relationship to a fixed vertical arm, the nut may be tightened and the
horizontal arm used in a fixed position.

2- The vertical arm of the Jelenko surveyor is spring mounted and returns to the
top position when it is released. It must be held down against spring tension
while it is in use. The vertical arm on the Ney surveyor is retained by friction
within a fixed bearing. The shaft may be moved up or down within this bearing
but remains in any vertical position until again moved. The shaft may be fixed in
any vertical position desired by tightening a set screw.

To some it is a disadvantage. The spring may be removed, but the friction of
the two bearings supporting the arm does not hold it in position as securely as
does a bearing designed for that purpose.

3- Reinforcing sheath present in Ney surveyor used to maintain the carbon
marker from breakage.

4- Jelenko surveyor has one undercut gauge with different ends but the Ney
surveyor has three different undercut gauge with different sizes.

4-Williams surveyor has Gimbal stage table that is adjustable to any desired
anterior, posterior, or lateral tilt. Degree of inclination can be recorded for
repositioning of cast at any time. Distinct advantage of this table over universal
tilt table is that center of rotation always remains constant. Superstructure of this
surveyor consists of jointed arm and spring-supported survey rod, all
components of which can be locked in fixed position if desired. This surveyor is
perhaps best suited for placement of internal attachments rather than for cast
analyzing and other purposes.



Because the shaft on the Ney surveyor is stable in any vertical position it may be
used as a drill press when a handpiece holder is added. The handpiece may thus
be used to cut recesses in cast restorations with precision by using burs or
carborundum points of various sizes in a dental handpiece.




                                                                  Mostafa Fayad - 4 -
                                                                   DENTAL SURVEYOR


Objectives of surveying


  Surveying of both the study and the master casts is essential for proper
diagnosis، designing and treatment planning. Surveying of the master cast
follows mouth preparations. The objectives of surveying are:

 1.    Permit an accurate charting of the required restorative procedures and
      mouth preparations.

 2.     Determine the most acceptable path of placement and removal which;

                a. Allows easy placement of the prosthesis and free from any
              interference .

               b. Avoids impingement of oral mucosa.

               c. Provides adequate clasp retention.

               d. Satisfies the requirements of guiding planes،

               e. Provides the best esthetic requirements.

 3.     Delineate height of contour (survey line) on the abutment teeth .

 4.     Determine soft، bony or tooth undercuts and areas of interferences that
      should be blocked out or eliminated.

 5.     Identify and measure tooth undercuts that may be used for retention and
      locate the flexible components in their position below the survey line of the
      tooth.

 6.     Determine the relative parallelism of teeth surfaces that act as guiding
      planes.

 7.     Recording the cast position in relation to a selected path of placement for
      future reference (tripoding or scoring).

 8.     Trimming blockout material on the master cast parallel to the path of
      placement prior to duplication.




                                                                  Mostafa Fayad - 5 -
                                                                   DENTAL SURVEYOR


PURPOSES OF SURVEYOR
       The surveyor may be used for surveying the diagnostic cast, recontouring
abutment teeth on the diagnostic cast, contouring wax patterns, measuring a
specific depth of undercut, surveying ceramic veneer crowns, placing
intracoronal retainers, placing internal rests, machining cast restorations, and
surveying and blocking out the master cast.

A - Surveying the diagnostic cast
1. To determine the most desirable path of placement that will eliminate or
minimize interference to placement and removal.

2. To identify proximal tooth surfaces that are or need to be made parallel so that
they act as guiding planes during placement and removal.

3. To locate and measure areas of the teeth that may be used for retention.

4. To determine whether tooth and bony areas of interference will need to be
eliminated surgically or by selecting a different path of placement.

5. To determine the most suitable path of placement that will permit locating
retainers and artificial teeth to the best esthetic advantage.

6. To permit an accurate charting of the mouth preparations to be made. This
includes the preparation of proximal tooth surfaces to provide guiding planes
and the reduction of excessive tooth contours to eliminate interference and to
permit a more acceptable location of reciprocal and retentive clasp arms. using
an undercut gauge to estimate the amount of tooth structure that may safely
(without exposing dentin) be removed ( marking these areas on the diagnostic
cast in red).

7. To delineate the height of contour on abutment teeth and to locate undesirable
tooth undercut areas that are to be avoided, eliminated, or blocked out. This
will include areas of the teeth to be contacted by rigid connectors, the location of
non retentive reciprocal and stabilizing arms, and the location of retentive clasp
terminals.

8. To record the cast position in relation to the selected path of placement for
future reference.




                                                                 Mostafa Fayad - 6 -
                                                                  DENTAL SURVEYOR


B- Contouring wax patterns
      The surveyor blade is used as a wax carver so that the proposed path of
placement may be maintained throughout the preparation of cast restorations for
abutment teeth.

      Guiding planes on all proximal surfaces of wax patterns adjacent to
edentulous areas should be made parallel to the previously determined path of
placement. Similarly, all other tooth contours that will be contacted by rigid
components should be made parallel.

      The surfaces of restorations on which reciprocal and stabilizing
components will be placed should be contoured to permit their location well
below occlusal surfaces and on non retentive areas.

        Those surfaces of restorations that are to provide retention for clasp arms
should be contoured so that retentive clasps may be placed in the cervical third
of the crown and to the best esthetic advantage.

C- Surveying ceramic veneer crowns
      The surveyor is used to contour all areas of the wax pattern for the
veneer crown except the buccal or labial surface.

       Before the final glaze is accomplished, the abutment crowns should be
returned to the surveyor on a full arch cast to ensure the correct contour of the
veneered portions or to locate those areas that need recontouring. The final glaze
is accomplished only after the crowns have been recontoured.

D- Placement of intracoronal retainers (internal attachments)
      1. To select a path of placement in relation to the long axes of the
abutment teeth that will avoid areas of interference elsewhere in the arch.

       2. To cut recesses in the stone teeth on the diagnostic cast for estimating
the proximity of the recess to the pulp (used in conjunction with roentgenograph
to estimate pulp size) and to facilitate the fabrication of metal or resin jigs to
guide the preparations of the recesses in the mouth.

      3. To carve recesses in wax patterns, to place internal attachment trays
in wax patterns, or to cut recesses in castings with the handpiece holder

       4. To place the keyway portion of the attachment in the casting before
investing and soldering; each keyway must be located parallel to the other
keyways elsewhere in the arch



                                                                Mostafa Fayad - 7 -
                                                                    DENTAL SURVEYOR


E- Placement of internal rest seats
       The surveyor may be used as a drill press, with a dental handpiece
attached to the vertical arm by a handpiece holder. Internal rest seats may be
carved in the wax patterns and further refined with the handpiece after casting,
or the entire rest seat may be cut in the cast restoration with the handpiece. It is
best to carve the outline form of the rest seat in wax and merely refine the
casting with the handpiece.

        Internal rest seats may be made in the form of a non retentive box, a
retentive box fashioned after the internal attachment, or a semi retentive box. [In
the latter the walls are usually parallel and non retentive, but a recess in the floor
of the box prevents proximal movement of the male portion. Small round burs
are used to cut recesses in the floor of the rest seat . Tapered or cylindrical
fissure burs are used to form the vertical walls].

       The ball-and socket, spoon-shaped occlusal or non interlocking rest
should be used in distal extension partial denture designs. The use of the dove-
tailed or interlocking internal rest should be limited to tooth-supported
removable restorations, except when it is used in conjunction with some kind of
stress-breaker between the abutments and the movable base.

F- Machining cast restorations
       With handpiece holder attached axial surfaces of cast and ceramic
restorations may be refined by machining with a suitable cylindrical
carborundum point. Proximal surfaces of crowns and inlays, which will serve as
guiding planes, and vertical surfaces above crown ledges may be improved by
machining, but only if the relationship of one crown to another is correct.

G- Surveying the master cast
1. To select the most suitable path of placement by following mouth
preparations that satisfy the requirements of guiding planes, retention,
noninterference, and esthetics

2. To permit measurement of retentive areas and to identify the location of
clasp terminals in proportion to the flexibility of the clasp arm being used.

 Retention depend on (a) the flexibility of the clasp arm, (b) the magnitude of the
tooth undercut (the magnitude of the angle of cervical convergence below the
point of convexity), and (c) the depth the clasp terminal is placed into this
undercut




                                                                  Mostafa Fayad - 8 -
                                                                    DENTAL SURVEYOR


 3. To locate undesirable undercut areas that will be crossed by rigid parts of
 the restoration during placement and removal; these must be eliminated by
 blackout

 4. To trim blockout material parallel to the path of placement before
 duplication

 Principles and Rules for Surveying

1. By surveying the prosthesis goes smoothly into place without interference

2. All casts are originally surveyed with the occlusal-plane parallel to the base of
    the surveyor (zero tilt).

3. When the surveyor blade contacts a tooth on the cast at its greatest convexity، a
    triangle is formed, the apex of the triangle is at the point of contact of the surveyor
    blade with the tooth, and the base is the area of the cast representing the gingival
    tissues. The apical angle is called the angle of cervical convergence. This will
    indicate the areas available for retention and the existence of tooth and other tissue
    interference to the path of placement.

4. A cast in a horizontal relationship to the vertical arm represents a vertical path of
    placement; a cast in a tilted relationship represents a path of placement toward
    the side of the cast that is tilted upward.

5. Any areas cervical to the height of contour may be used for the placement of
    retentive clasp components, whereas areas occlusal to the height of contour may
    be used for the placement of non-retentive, stabilizing or reciprocating
    components.

6. Whenever possible, undesirable undercuts and areas of interference are removed
    during mouth preparation by recontouring teeth or making necessary restorations.

7. The location of the undercut area can be changed by tilting the cast anteriorly or
    laterally.

8. Deciding the tilt of the cast depends on path of placement and removal.

9. A combination between two tilts could be used.

10. An anterior tilt is sometimes preferred in distal extension bases this increases
    resistance to vertical displacement by the denture base by engaging undercuts
    distal to abutment teeth.




                                                                   Mostafa Fayad - 9 -
                                                                      DENTAL SURVEYOR


11. The retentive tips of clasps must engage undercuts, which are present, when the
     cast is surveyed with the occlusal plane parallel to the base of the surveyor، i.e.
     undercut areas should be present at both zero tilt and the new tilt

12. The retention on all principal abutments should be as nearly equal as possible.

13. Without guiding planes, clasp retention will either be detrimental or practically
     nonexistent.




 Uniform clasp retention depends on depth (amount) of tooth undercut rather than on
 distance below the height of contour at which clasp terminus is placed.




 The fallacy of attempting to create retentive undercuts by tilting the cast on the
 surveyor

A.      No retentive undercut on the buccal surface of the abutment.

B.      The cast is tilted to create an under-cut.

C.      The clasp tip engages this created undercut.

D.     During mastication the dislodging force will be perpendicular to the
 occlusal plane and since the retentive undercut is not present, in this plane, the
 prosthesis is dislodged.




                                                                   Mostafa Fayad - 10 -
                                                                         DENTAL SURVEYOR




                                               D



Clasps designed at tilt are ineffective without development of corresponding guide planes to
resist displacement when restoration is subject to dislodging forces in occlusal direction.




Step by step procedures in surveying and determination of
the path of placement:
       a)      Placement of the cast: The cast is attached to adjustable
      surveyor table by means of the clamp provided, in a horizontal position
      (zero ti1t).

       b)     Guiding planes: Analyze the proximal abutment tooth surfaces
      with the surveyor-analyzing rod. Alter the cast position
      anteroposteriorly until their proximal surfaces are in parallel relation
      to one another or near enough that they can be made parallel by
      recontouring. The end result should provide parallel proximal surfaces that
      may act as guiding planes.

       c)     Retentive areas: By contacting buccal and lingual surfaces of
      abutment teeth with the surveyor blade, the amount of retention existing
      below their height of convexity may be determined. This is best
      accomplished by directing a small source of light toward the cast from
      the side away from the dentist. The angle of cervical convergence is best
      observed as a triangle of light between the surveyor blade and the apical
      portion of the tooth surface being studied .

              Alter the cast position by tilting it laterally until similar retentive
       areas exist on the principal abutment teeth.

        If only two abutment teeth are involved, as in a Kennedy Class I partially
      edentulous arch, they are both principal abutments. However, if four
      abutment teeth are involved (as they are in a Kennedy Class III,
      modification 1 arch), they are all principal abutments, and retentive areas


                                                                       Mostafa Fayad - 11 -
                                                                    DENTAL SURVEYOR


     should be located on all four. But if three abutment teeth are involved (as
     they are in a Kennedy Class I I , modification 1 arch), the posterior
     abutment on the tooth-supported side and the abutment on the distal
     extension side are considered to be the principal abutments, and retention
     needs to be equalized accordingly. The third abutment may be considered
     to be secondary, and less retention is expected from it than from the other
     two.

       An exception is when the posterior abutment on the tooth-supported side
     has a poor prognosis and the denture is designed to ultimately be a Class I.
     In such a situation, the two stronger abutments are considered to be
     principal abutments.

              In tilting the cast laterally, it is necessary that the table be rotated
       without disturbing the anteroposterior tilt previously established.



      d) Interferences: It should be noted that areas of interference to proper
     placement of clasp arm can be eliminated by reshaping tooth surfaces
     during mouth preparations.

       If there is bilateral soft، bony or tooth interferences that may prevent the
     insertion and removal of rigid connector, surgery and/or recontouring of
     lingual tooth surfaces may be unavoidable. If interference is only
     unilateral, change the path of insertion at the expense of guiding planes and
     retention.

      e)     Esthetics: If a choice between two paths of equal merit, one
     permits a more esthetic placement of clasp arms than the other, that path
     should be preferred.

      f) After selection of the proper path of insertion, the cast is secured in
     place before the following steps are made
1. Drawing of the survey line

The analyzing rod is replaced with a carbon marker and the survey line is drawn
on abutment teeth.

2. Location of the clasp terminals

       The carbon marker is removed from the tool holder and the suitable
undercut gauge is fixed in the holder. The undercut gauge is placed in contact
with the tooth to be clasped with its shaft touching the tooth surface at the survey


                                                                 Mostafa Fayad - 12 -
                                                                        DENTAL SURVEYOR


line. The head will indicate the undercut area where the clasp will terminate. A
sharp pencil is used to mark this point.

      It is preferable that undercuts be present on both zero tilt and lateral tilt to
avoid creation of apparent undercuts. Retentive terminals located in apparent
undercuts will be displaced by occlusally displacing forces.

3.Blocking the undesirable undercuts

      The undesirable undercuts especially on the proximal surfaces are filled
with wax. The wax trimmer is fitted in the tool holder to trim the excess wax.

4.Tripoding or scoring the cast to preserve the established cast tilt.

      All these steps are performed while the master cast is still mounted on the
survey table without changing the tilt.



                                         Recommended method for manipulating dental
                                    surveyor Right hand is braced on horizontal arm of
                                    surveyor، and fingers are used, as illustrated, to raise
                                    and lower vertical shaft in its spindle. Left hand
                                    holding cast on adjustable table slides horizontally on
                                    platform in relation to vertical arm. Right hand must
                                    be used also to loosen and tighten tilting mechanism
                                    as suitable anteroposterior and lateral tilt of cast in
                                    relation to surveyor is being determined.




Recording the cast position:
        Preserving the established cast tilt in relation to the selected path of
insertion and repositioning of the cast on the surveyor table to its original
position is performed by rather of the two methods .

 Tripoding:

        Tripoding is done by drawing three widely separated cross marks on the
tissue side of the cast lingual or palatal to the remaining natural teeth while the
cast and the vertical arm is locked at a certain vertical height. The cast can be
repositioned to the same tilt by allowing the analyzing rod to touch one of the
cross marks, the spindle is then locked at this vertical height and the tilt of the


                                                                     Mostafa Fayad - 13 -
                                                                   DENTAL SURVEYOR


cast is modified until the rod touches the three cross marks. Then locking the
surveyor table.




                                                          A, Tripoding the cast




 Scoring : analyzing rod method

Two sides and the dorsal aspect of the base of the cast are scored with a sharp
instrument held against the surveyor blade. By tilting the cast until all three lines
are parallel to the surveyor blade, the original tilt can be re-established.



                                                             B, Scoring the cast




                                                                Mostafa Fayad - 14 -
                                                                    DENTAL SURVEYOR


                          Path of Placement (Insertion)
         It is the specific direction in which a prosthesis is placed on the abutment
teeth.

       The path of insertion of the partial denture is "The direction of
movement in which a prosthesis moves from the point of initial contact with the
supporting teeth to the terminal resting position where the occlusal rests are
seated and the denture base is in contact with the tissues".

      The path of removal of the partial denture is "The direction of
movement of the restoration from its resting position to the last contact with the
supporting teeth". It is the reverse of the path of insertion.

         Types of path of insertion

         1. Single path

       Two or more parallel axial surfaces on abutment teeth which can be used
to limit the path of insertion and improve the stability of a removable prosthesis.
Guide surfaces may occur naturally on teeth but more commonly need to be
prepared.

         2. Double path

       Two distinct paths of insertion will be employed for a sectional, or two-
part denture illustrated here by a diagram in the sagittal plane of a Kennedy
Class IV denture. The abutment teeth on either side of the saddle are not shown.

         3. Multiple path:

       Multiple paths will also exist where point contacts between the saddle of
the denture and the abutment teeth are employed in the ‘open’ design of saddle.

         4. Rotational path

       A single path of insertion may be created if sufficient guide surfaces are
contacted by the denture; exist mostly in bounded saddle.

        Multiple paths of insertion will be exist where guide surfaces are not
utilized where the abutment teeth are divergent or where point contact between
the saddle and the abutment teeth is employed.




                                                                 Mostafa Fayad - 15 -
                                                                       DENTAL SURVEYOR


    Factors Affecting Path of Insertion of the Partial Denture

    1-Interferences: The prosthesis must be designed so that it may be placed and
    removed without encountering any tooth or tissue interferences.

    Interferences may be eliminated during mouth preparation by either:

            a) Changing the path of placement.

            b) Relief of the denture.

            c) Alters tooth Contours with restorations.

            d) Extraction.

            e) Surgery to remove interfering structures as bony exostosis, tori or
            undercuts.

            f) A combination of any one of the above.

    2-     Retentive undercuts

          Retentive undercuts must be present on the abutment teeth, both at the
    horizontal (zero) tilt and at the tilt of the selected path of placement, to counteract
    any dislodgment of the denture in that direction.

           Those undercuts should be equal in depth and should also permit the
    location of clasp tips in the gingival third of the tooth. The tilt is normally
    changed to lower the height of contour on an abutment tooth so that the clasp
    arms, retentive or reciprocal, can be positioned no more occlusal than the
    junction of the gingival and middle third of the tooth. This position is more
    esthetic and lowering the torque forces transmitted to the tooth by the clasp

-         Retentive clasp arms must be located so that they lie in the same
    approximate degree of undercut on each abutment tooth. Clasp retention is no
    more than the resistance of metal to deformation.

-          Retention should be the minimum acceptable only to resist reasonable
    dislodging forces.

-            Retentive surfaces may be made by altering tooth contours or by
    placing cast restorations with similar contours.

-          The size of the angle of convergence will determine how far into that
    angle a given clasp arm should be placed. Retention will depend on the location
    of the retentive part of the clasp arm, not in relation to the height of contour, but
    in relation to the angle of cervical convergence.


                                                                    Mostafa Fayad - 16 -
                                                                  DENTAL SURVEYOR


-      Retention may be obtained by one or two means:

1- Change the path of placement to increase or decrease the angle of cervical
convergence of opposing retentive surfaces of abutment teeth.

2- Alter the flexibility of the clasp arm by changing its design, its size, and
length or the material of which it is made.



3-     Health of teeth used as abutment

       For example, in tooth-bearing dentures, if the molar is weaker than the
bicuspid, an anterior tilt may be advisable, in order to place the clasp on the
stronger tooth.

4- Esthetics:

        The retentive area should be selected with the most esthetic clasp
location. The most esthetic placement of artificial teeth is made possible with
less clasp metal and less base material displayed.

      A vertical path of placement is necessary when missing anterior teeth
must be replaced to avoid modifying the natural teeth.

5- Guiding planes:

        Guiding planes are formed by two or more parallel axial surfaces on
abutment teeth which can be used to limit the path of insertion and improve the
stability of a removable prosthesis. Guide surfaces usually need to be prepared.

      Proximal tooth surfaces that bear a parallel relationships to one another
must either be found or be created to act as guiding planes during placement and
removal of the prosthesis.




When anterior teeth must be replaced with partial denture vertical path of placement
may be necessary to avoid excessively altering abutment teeth and supplied teeth.




                                                                Mostafa Fayad - 17 -
                                                                     DENTAL SURVEYOR


Selection of the Path of Insertion
        The most favorable path of insertion is that perpendicular to the
occlusal plane, Survey analysis should start first with the occlusal plane parallel
to the base of the surveyor (zero tilt). This path is preferred because most
patients tend to seat their dentures under biting force. However, this inclination
(zero tilt) may not be convenient with respect to the factors affecting selection of
the path of insertion.

       Thus, if undercuts are present but not efficient at the zero tilt and if
displacement of the prosthesis is anticipated with the least displacing forces,
another path of insertion should be decided. This is achieved either by:

       1- A rotating or curved path: In this path one section of the prosthesis is
seared first and the remainder is then rotated into position.

       2- Tilting the cast to:

            a-        Create suitable undercuts.

            b-        Equalize undercuts on both sides of the arch.

            c-        Place the clasp tips in a better esthetic position.

The path of placement may also be slightly off of the zero tilt to allow for
reduction in the amount of undercut when rigid minor connectors contacting
guiding planes are planned to help in providing retention.

       Since the path of dislodgment resulting at the end of each masticatory
cycle tends to pull the denture on a direction perpendicular to the occlusal plane,
therefore, undercut areas should be present at both zero tilt and the new tilt,
Gross inclination of the cast to create apparent undercuts should be avoided.




                                                                  Mostafa Fayad - 18 -
                                                                           DENTAL SURVEYOR




                 Blocking Out and Relief of the Master Cast:
        After the establishment of the path of placement and the location of
undercut areas on the master cast, any undercut areas that will be crossed by
rigid parts of the denture (which are every part of the denture framework except
the retentive clasp terminal) must be eliminated by block out.

       In the broader sense of the term, blockout includes not only the areas
crossed by the denture framework during seating and removal but also (1) those
areas not involved that are blocked out for convenience; (2) ledges on which
clasp patterns are to be placed; (3) relief beneath connectors to avoid tissue
impingement; and (4) relief to provide for attachment of the denture base to the
framework.

      Severe undercuts in retromylohyoid or buccal regions of the cast have to
be blocked-out to prevent possible distortion of duplicating mould when the
master cast is removed.




                                                    All guiding planes areas must be parallel
                                                to the path of placement and all other areas
    All guiding planes areas must be parallel   that will be contacted by rigid parts of
to path of placement and all other areas that   framework must be made free of undercut by
will be contacted by rigid parts of dentures    parallel blockout. Relief also must be
frameworks must be made free of undercut        provided for the gingival crevice and
by parallel blockout.                           gingival margin.




                                                                        Mostafa Fayad - 19 -
                                                                  DENTAL SURVEYOR


PARALLELED BLOCKOUT, SHAPED BLOCKOUT, ARBITRARY
BLOCKOUT, AND RELIEF

Paralleled blockout

   1. Proximal tooth surfaces to be used as guiding planes.

   2. Beneath all minor connectors.

   3. Tissue undercuts to be crossed by rigid connectors.

   4. Tissue undercuts to be crossed by origin of bar clasps.

   5. Deep interproximal spaces to be covered by minor connectors or
      linguoplates beneath bar clasp arms to gingival crevice.

Shaped blockout

         1. On buccal and lingual surfaces to locate plastic or wax patterns for
            clasp arms.

         2. Ledges for location of reciprocal clasp arms to follow height of
            convexity so that they may be placed as cervical as possible
            without becoming retentive.

         3. Ledges for location of retentive clasp arms to be placed as cervical
            as tooth contour permits; point of origin of clasp to be occlusal or
            incisal to height of convexity، crossing survey line at terminal
            fourth, and to include undercut area previously selected in keeping
            with flexibility of clasp type being used

Arbitrary blockout (Smoothed arbitrarily with wax spatula)

         1. All gingival crevices

         2. Enough to just eliminate gingival crevice Leveled arbitrarily with
            wax spatula

         3. Gross tissue undercuts situated below areas involved in design of
            denture framework

         4. Tissue undercuts distal to cast framework

         5. Labial and buccal tooth and tissue undercuts not involved in
            denture design




                                                                Mostafa Fayad - 20 -
                                                              DENTAL SURVEYOR


Relieving the Master Cast:

             1. Beneath lingual bar connector.

             2. Areas in which major connectors will contact thin tissues such
                as hard areas so frequently found on the lingual surface of the
                mandibular ridges and elevated median palatal raphes.

             3. Beneath framework extensions onto ridge areas for attachment
                of resin bases.




                                                            Mostafa Fayad - 21 -
                                                                   DENTAL SURVEYOR


                              SURVEY LINES
      A SURVEY LINE is a line produced on a cast by a surveyor or scribe
marking the greatest prominence of contour in relation to the planned path of
placement of a restoration.1

       A survey line marks the HEIGHT OF CONTOUR (greatest prominence)
of a tooth or bony prominence AT THE SELECTED PATH OF PLACEMENT
of the denture (TILT OF THE CAST). If the tilt of the cast is changed (changing
the path of placement of the denture) the height of contour (survey line) will
change.

       IDENTIFYING SURVEY LINES

       Survey lines are marked on a cast by first orienting the cast in the cast
holder at the tilt indicating the path of placement for the denture and then sliding
the cast holder along the surveyor table so that the cast surface is lightly rubbed
against a carbon marker held in the chuck in the spindle of the surveyor .

       Survey lines are marked on non-polished metal and non-glazed porcelain
crown surfaces with a carbon marker in a similar fashion.

       Survey lines are marked on wax patterns for crowns by dusting the
surface with zinc stearate or powdered white wax, then sliding the cast holder on
the surveyor table so that the surface of the wax pattern is lightly rubbed against
an analyzing rod held in the chuck in the spindle of the surveyor.

       Survey lines are marked on polished metal and glazed porcelain crown
surfaces in a similar manner substituting a layer of disclosing medium
(i.e.Occlude, Die Mark, etc.) on the surface of the crown.

       USES OF SURVEY LINES

       Survey Lines on Teeth

       The survey line on the facial and lingual of abutment teeth is important in
selecting clasps and planning the modifications of the teeth necessary for the
selected clasps.

      The survey line on the proximal tooth surface is important to minor
connector design.

      The survey line on non-abutment teeth involved in the RPD design is
important in selecting and designing major and minor connectors.




                                                                Mostafa Fayad - 22 -
                                                                   DENTAL SURVEYOR


              Survey Lines on Bony Prominences

        Survey lines are marked on all bony and soft tissue prominences located
in the area of the denture. These lines are important in the selection, location,
and design of major and minor connectors, and bar clasp approach arms,

       CLASSIFICATION OF SURVEY LINES

       Blatterfein divided the buccal and lingual surface of the tooth adjacent to
the edentulous area into two halves by a line passing through the center of this
surfaces along the vertical axis of the tooth .

       The area closer to edematous area called near zone and the area away
from the edematous area called far zone.

       Survey lines can be classified as:

           High survey line

           Medium survey line

           Low survey line

           Diagonal survey line.

       High survey line :

       High survey line passes from the occlusal third in the near zone to the
occlusal third in the far zone. When a high survey line is present, the undercut
will be deep and hence a wrought wire clasp which is more flexible should be
used.

      It is commonly found in inclined teeth and in teeth with a larger occlusal
diameter compared to its diameter at the cemento-enamel junction.

       Medium survey line

        It passes from the occlusal third in the near zone to the middle third in
the far zone – Either Aker's or Roach clasp is used for teeth with a medium
survey line. Aker's clasp is preferable. During survey, the cast should be tilted
such that maximum number of teeth have a medium survey line.

       Low survey line

       This survey line is closer to the cervical third of the tooth in both near and
far zone. A modified T-clasp is used for teeth with low survey lines.




                                                                 Mostafa Fayad - 23 -
                                                                  DENTAL SURVEYOR


        It is common in teeth with marked inclination, when it is associated with
a high survey line on the opposite side. The retentive clasp tip cannot be placed
in such cases, because the undercut will be very close to the gingiva and difficult
to maintain oral hygiene.

       In such cases one of the following designs can be followed.

           A bracing or reciprocal arm is placed along the low survey line and
            a retentive wrought wire clasp is placed to engage the undercut on
            the opposite side.

           Extended clasp can be used.

           Re-contouring the tooth with a crown can be done.

           Proximal undercut can be used for retention.

       Diagonal survey tine

        This survey line runs from the occlusal third of the near zone to the
cervical third of the far zone. Here, a reverse circlet clasp is used. It is more
common on the buccal surfaces of canines and premolars. It can be managed by
using reverse action (hair pin) or ring type Aker's clasp (occlusally approaching)
, or L or T type roach clasp (gingivally approaching).




                                  Undercuts


       The term undercut, when used in reference to an abutment tooth, is that
portion of a tooth that lies between the height of contour and the gingivae.

       When used in reference to other oral structures, it means the contour or
cross section of residual ridge or dental arch that would prevent the placement of
a denture.

        Generally, a small amount of undercut 0.02 inch (0.375 mm) or less is
sufficient for retentive purposes.

       The gingival retentive zone : It is triangular area bounded by horizontal
flange and vertical arm of undercut gauge and tooth surface.

       Depth of under cut: the horizontal measured by undercut gauge


                                                               Mostafa Fayad - 24 -
                                                                 DENTAL SURVEYOR


      Distance of undercut: the vertical distance between the flange of undercut
gauge and survey line

      Retention depend on

      (a) the flexibility of the clasp arm,

       (b) The magnitude of the tooth undercut (the magnitude of the angle of
cervical convergence below the point of convexity), and

      (c) The depth the clasp terminal is placed into this undercut

Partially edentulous mouth has many undercut areas that result due to:

    a- Bulbous shape of the crowns of natural teeth resulting in buccal and
    lingual undercuts.

    b- The inclination of the long axes of teeth in relation to a vertical line
    drawn from the occlusal surface, resulting in undercut on the proximal
    surfaces of these teeth.

    c- The inclination of soft tissues or bone to a vertical line drawn from the
    occlusal surface resulting in soft tissue or bony undercuts.

    d- Proliferation of soft tissues covering the edentulous ridge due to the
    rapid pattern of bone resorption .



The undercuts might be:

1) Desirable undercuts:

       Desirable undercuts are used for retaining the partial denture against
dislodging forces. Discerning the angle of cervical convergence is important in
developing uniform retention through clasps.

2) Undesirable undercuts:

      Undercuts other then those used for retention are considered undesirable
and should be eliminated. This done by

           Blocking out the undercut with wax on the master cast .

           preparation and reduction of the tooth surface in the mouth

           Placing properly contoured crown restoration




                                                              Mostafa Fayad - 25 -
                                                                DENTAL SURVEYOR


The under cut may be classified into

      True undercut : which present in relation to analizing rod and in relation
to undercut in opposite side. Desirable undercuts must be present at the path of
placement of the RPD.

       False undercut: Tilting the cast away from the path of placement of the
RPD may create undercuts, but these are FALSE UNDERCUTS because they do
not provide retention (resistance to movement of the prosthesis away from the
tissues along the path of placement and removal of the denture) since they are
not present along the path of placement and removal of the denture.

       The amount of undercut is measured in hundredths of an inch, with the
gauges allowing measurements up to 0.03 inch. Theoretically the amount of
undercut used may vary with the clasp to be used up to a full 0.03 inch.
However, undercuts of 0.01 inch are often adequate for retention by cast
retainers.

        Tapered wrought-wire retention may safely use up to 0.02 inch without
inducing undesirable torque on the abutment tooth, provided the wire retentive
arm is long enough (at least 8 mm). The use of 0.03 inch is rarely, if ever,
justified with any clasp. When greater retention is required, such as when
abutment teeth remain on only one side of the arch, multiple abutments should
be used rather than increasing the retention on anyone tooth.

                              Guiding planes
       Guiding planes are flat axial surfaces in an occluso-gingival direction on
the proximal or lingual surfaces of teeth. They are made parallel to the path of
placement, help in guiding the prosthesis during placement and removal.

       They are prepared on the enamel surface after the path of Insertion is
selected according to the other three factors.

      A guide surface should be produced by removing a minimal and fairly
uniform thickness of enamels usually not more than 0.5 mm, from around the
appropriate part of the tooth. It should extend vertically for about 3 mm and
should kept far from the gingival margin

       They are 2 - 4 mm in height, and extend bucco-lingually according to the
width of the component that is contacting them.

       Guiding plane surface should be like area of cylindrical object. It should
be continuous surface unbounded by even rounded line angle.



                                                             Mostafa Fayad - 26 -
                                                                    DENTAL SURVEYOR


       Minor connector contacting guiding plane surface has same curvature as
does that surface. From occlusal view it tapers buccally from thicker lingual
portion, thus permitting closer contact of abutment tooth and prosthetically
supplied tooth. Viewed from buccal aspect, minor connector contacts enamel of
tooth on its proximal surface about two-thirds its length.




        Prevention of clasp deformation; without guide surface the patient may
tilt or rotate the denture on removal causing the clasp to flex beyond their
proportional limit

       A guide surface allows a reciprocating component to maintain continuous
contact with a tooth as the denture is displaced occlusally. The retentive arm of
the clasp is thus forced to flex as it moves up the tooth. It is this elastic
deformation of the clasp, which creates the retentive force.

       Increased stability is achieved by the guide surfaces resisting
displacement of the denture in directions other than along the planned path of
displacement.




Components of the denture that contacts the guiding planes during
placement are:

I-Those contacting proximal surfaces:

a.     The minor connector that joins the clasps to the saddle.

b.     Proximal plates that are used with I-bar or RPI clasps.

II. Those contacting axial (lingual) surfaces:



                                                                  Mostafa Fayad - 27 -
                                                                  DENTAL SURVEYOR


a.     Reciprocal clasp arms.

b.     Lingual plates that act as reciprocal arms.

c.     Minor connectors that join the auxiliary rests to the major connector.



The benefits of the guiding planes include

1- Guide the prosthesis for easier path of placement and removal.

2- Eliminate detrimental strain to the framework components and minimize
   wedging stresses on the abutment teeth (Fig.6-10).

3- The frictional contact of the prosthesis against these parallel surfaces can
   contribute significantly to the overall retention of the prosthesis، and
   assisting the reciprocal clasp arm to perform its intended function.(Fig.6-11)

4- Aid in stabilizing the prosthesis against horizontal stress (Fig.6-12). Guiding
   planes are particularly effective when the edentulous spaces are tooth
   bounded.

5- Well-prepared guiding planes tend to reduce undercuts between the proximal
   surface of the teeth and the minor connectors of the partial denture, thus
   making the prosthesis more hygienic.

6- A properly prepared guiding plane lowering the height of contour of the
   proximal surface of the tooth permits the placement of some of the rigid
   portion of the clasp closer to the gingival margin of the tooth. This
   provides a more esthetic and biomechanical advantages (How).



Guiding planes and the distal extension base:

        For bounded base a well-engineered guiding planes are contacted by the
proximal plates of the framework as the prosthesis is inserted and removed, thus
horizontal wedging is virtually eliminated. and all transverse stresses transmitted
to the tooth are effectively neutralized.

       In contrast to this the creation of a flat distal surface on the abutment
tooth next to an edentulous space in distal extension case has the effect of
magnifying the stress that the denture base transmits to the abutment as the base
moves in function.




                                                               Mostafa Fayad - 28 -
                                                               DENTAL SURVEYOR


       A pronounced guiding plane is not recommended for the abutment
tooth that supports a distal extension base to decrease the stress that the
denture base transmits to the abutment as the base moves in function.

       The interface between the tooth surface and the clasp should be such that
a slight degree of movement of the base and the clasp is permitted without
transmitting torsional stress to the tooth.

       Enough flattening of the distal surface of the tooth should be
accomplished to reduce the amount of the undercut between the minor connector
and the abutment tooth.




A) For bounded base a well-engineered guiding planes are contacted by the
truss arms of the framework. B:F، the proximal plates engages the bottom of 1 to
2 mm. of guide plane and is meant to vertically disengage with extension base
loading




                                                             Mostafa Fayad - 29 -
                                                               DENTAL SURVEYOR




Diagrammatic illustration showing comparative width of the proximal plates for
differently contoured teeth. (A). Proximal plate (p) relatively wide due to the
square contour of the 2nd bicuspid. (B). Proximal palate (p) relatively narrow
due to the tapering contour of the 1st bicuspid.



         Guiding planes are most effective when they are :

           parallel

         Include more than one common axial surface (e.g. proximal and
          lingual surfaces)

         Are directly opposed by another guiding plane (e.g. facing guiding
          planes in a modification space)

         Are placed on several teeth

         Cover a large surface area (long and/or broad)

         Should be at least 1/2 to 1/3 of the axial height of the tooth
          (generally a minimum of 2 mm in height).

         Guide planes for distal-extension cases should be slightly shorter to
          avoid torquing of the abutment teeth.

         Lingual guiding planes for bracing or reciprocal arms should be 2-4
          mm and ideally be located in the middle third of the crown, occluso
          - gingivally.




                                                             Mostafa Fayad - 30 -
                                                      LABORATORY PROCEDURES




LABORATORY PROCEDURES FOR FRAMEWORK CONSTRUCTION


    The construction of metallic removable partial dentures comprises both
clinical and laboratory steps that are done following the sequence shown in the
previous table.

The laboratory steps include:
   1- Construction of the study cast
   2- Primary surveying the study cast
   3- Construction of a customized tray
   4- Construction of the master cast
   5- Surveying of the master cast
   6- Drawing the design on the master cast
   7- Preparation of the master cast
         a) Spraying the master cast
          b) Beading the maxillary master cast
          c) Waxing the master cast:
              Blocking-out the undesirable undercuts
             Relief
             Tissue Stops
             Formation of internal finishing lines
   8- Duplication
   9- Waxing the framework on the refractory cast
   10-Sprueing the Framework
   11-Investing the sprued pattern
   12-Burnout of the wax pattern
   13-Casting the partial denture framework
   14-Finishing and Polishing of the framework
   15-Fitting the framework to the cast
   16-Processing of acrylic resin.




                                                                  Mostafa Fayad 1
                                                           LABORATORY PROCEDURES



    1-Construction of the study cast:
           It is a positive reproduction of the form of the dental arch. It is obtained
    by pouring the preliminary impression using dental stone to avoid abrasion or
    fracture during handling. It should accurately reproduce the remaining teeth,
    residual ridge and the adjoining structure.

    Uses of diagnostic cast:
           Maxillary and mandibular diagnostic casts can be mounted using an
    inter-occlusal registration record to serve the following purposes:
       1 Diagnosis and treatment planning
       2 Evaluation of the occlusion and the need for any occlusal adjustments.
       3 Surveying and design drawing.
       4 Provides information on the need for mouth and abutment preparations.
       5 Case presentation and patient discussion.
       6 Patient records for future reference.
       7 Construction of special tray.

    2-Primary surveying the study cast:
        The study cast is surveyed using a dental surveyor to:
-         Permit an accurate charting of the required mouth preparations.
-         Determine desirable and undesirable undercuts.
-         Determine proximal tooth surfaces used as guiding planes.
-         Determine the best path of placement and removal of the prosthesis.


    3-Construction of a customized tray:
-         Acrylic resin is the material of choice but shellac tray may be used.
-         Spacer is adapted to the cast and trimmed to the proper peripheral
    outline. It is made of two layers wet asbestos. Wax or clay might also be used.
           The wax spacer is omitted on the buccal shelf of bone in the mandible in
    order to gain more support from this 1ry stress bearing area.
-
     4-construction of the master cast:
         After mouth preparation the final impression is recorded. The impression
    is poured in hard stone to obtain the master cast.
       The master cast is obtained by pouring the final impression using type IV
    (extra hard) dental stone because of its superior properties such as higher
    abrasion resistance, higher strength and less dimensional changes.



                                                                         Mostafa Fayad 2
                                                      LABORATORY PROCEDURES


   The cast is then allowed to final set 40 to 60 minutes before it is separated.
Proper trimming is also essential.
   The master cast should be duplicated into working cast with the same type
of stone) type IV). The procedures from now on will be carried out on the
working cast while keeping the master cast as a reserve should any damage
occurs. However, the terms master cast and working cast will be used
synonymously.
   Uses of master cast
          1 Construction of record blocks for jaw relation record.
          2 Second surveying in the same tilt of the first surveying.
          3 Design drawing as has been planned for.
          4 Preparation and duplication into refractory cast.

5- Surveying of the master cast:
  The master cast is surveyed to determine:
     1- Determine the most acceptable path of placement and removal which is
       free from any interference and، satisfy the requirements of guiding
       planes، retention، noninterference and esthetics.
     2- Determine soft، bony or tooth undercuts and areas of interferences that
       should be blocked out or eliminated
     3- Determine the relative parallelism of teeth surfaces that act as guiding
        planes.
     4- Identify and measure tooth undercuts that may be used for retention and
        locate the flexible components in their position below the survey line of
        the tooth.
     5- Aid in determining restorative procedures and mouth preparation.
     6- Delineate height of contour (survey line) on the abutment teeth.
     7- Trimming blockout material parallel to the path of placement prior to
        duplication.
     8- Recording the cast position in relation to a selected path of placement
        for future reference (tripod).
6-Drawing the design on the master cast:
     The outline form of the partial denture framework is carefully drawn on
       the master cast guided the design present on the study cast.




                                                                   Mostafa Fayad 3
                                                    LABORATORY PROCEDURES



7-Preparation of the master cast:
    The master cast should be modified prior to its duplication as follows:
       a) Spraying.
        b) Beading.
        c) Blockout.
        d) Relief.


    a) Spraying the master cast:
    The working cast is sprayed with sealer spray for the following purposes:
       a) Protection of the cast and drawn design from scratching,
       b) Providing the cast with smooth surface before duplication.
       c) Preventing the cast from absorbing the water of the colloid (agar)
    duplicating material.

    b) Beading the maxillary master cast:
        Beading is accomplished with a small spoon excavator by scraping
    along the anterior and posterior borders of the major connector.
        Beading depth and width should not exceed 0.5 to 1 mm and should
    fade out (beveled) as the gingival margins or a prominent area in the
    midline of the palate are approached.
         Beading on the borders of maxillary major connectors serves to
    prevent food particles from collecting beneath the framework and
    producing discomfort to the patient. The beading is also used by
    prosthodontists to help in transferring the major connector design to the
    investment cast.
        Beading is not done along the borders of the mandibular major
    connectors because of the thin underlying mucosa that cannot tolerate
    positive contact.
        The aim of beading is to:
    a) Compensate for metal solidification shrinkage and hence, ensures
    positive contact of the metal with palatal tissues.
    b) Prevent food particles from collecting under the RPD.
    c) Better for pronunciation.
    d) Help in transferring the design to the refractory cast.




                                                                  Mostafa Fayad 4
                                                      LABORATORY PROCEDURES



     c) Waxing the master cast:


      1- Blocking-out the undesirable undercuts:
              The elimination of undesirable undercuts on the master cost
          before duplication has different forms: paralleled blockout, shaped
          blockout and arbitrary blockout. There are three patterns of block out


        Paralleled blockout
      The blockout wax is trimmed parallel to the path of insertion and
  removal by using the wax trimmer surveyor tool while the cast is positioned
  in the predetermined tilt. It is done in the following areas:
-     Proximal tooth surfaces to be used as guiding planes
-     Beneath all minor connectors
-     Tissue undercuts to be crossed by rigid connectors
-     Tissue undercuts to be crossed by origin of bar clasps
-       Deep interproximal spaces to be covered by minor connectors or
    linguoplates beneath bar clasp arms to gingival crevice


    Shaped blackout
      It is done in the form of ledges on the buccal and lingual surfaces of
  abutment teeth. It will help in proper positioning and carving of the clasp
  arms.
-     On buccal and lingual surfaces to locate plastic or wax patterns for clasp
  arms.
-     Ledges for location of reciprocal clasp arms to follow height of convexity
  so that they may be placed as cervical as possible without becoming retentive
-     Ledges for location of retentive clasp arms to be placed as cervical as
  tooth contour permits; point of origin of clasp to be occlusal or incisal to
  height of convexity, crossing survey line at terminal fourth, and to include
  undercut area previously selected in keeping with flexibility of clasp type
  being used.

    Arbitrary blockout (Smoothed arbitrarily with wax spatula)
     This will cover the undercuts that may interfere with removal of the
  duplicating material otherwise it may be subjected to tearing or distortion.
  This includes:
-    All gingival crevices
-    Enough to just eliminate gingival crevice Leveled arbitrarily with
  wax spatula


                                                                   Mostafa Fayad 5
                                                              LABORATORY PROCEDURES


  -    Gross tissue undercuts situated below areas involved in design of
    denture framework
  -    Tissue undercuts distal to cast framework
  -    Labial and buccal tooth and tissue undercuts not involved in denture
    design

      2-Relief
          It is done for creating a space between the metal framework and the cast
  as in the following areas:
-        Beneath lingual bar connectors or the bar portion of linguoplates
  when indicated
-        Areas in which major connectors will contact• thin tissue such as hard
  areas so frequently found on lingual side of mandibular ridges and elevated
  median palatal raphea.
-       Beneath framework extension onto ridge areas for attachment of resin
  bases

      3-Tissue Stops:
            Tissue stops is done by removal of two small squares of 2 mm,
       usually an anterior and posterior, of relief wax at the distal end the
       edentulous ridge. It provides stability of the framework during clinical
       work and during acrylic resin processing.
            They will result in metal projections resting on ridge areas. Hence,
       the framework maintains its position while being subjected to the pressure
       of packing later on.




 Arrows indicate three small “nail head” minor connectors in which individualized impression
    trays may be attached when secondary impression is used.




                                                                             Mostafa Fayad 6
                                                        LABORATORY PROCEDURES



     4-Formation of internal finishing lines:
                  Internal finish lines are carved in the relief wax covering the
            edentulous ridge at the metal resin junction. This line is trimmed with
            blade held at 900 to the cast surface in order to produce a sharp
            junction having a uniform depth of at least 1mm.


8- Duplication
       Duplication is the procedure of accurately reproducing a cast.The
modified master cast is duplicated to form a refractory cast made of investment
material.
   A duplicating flask is used for this procedure. The most commonly used
material for duplication is the reversible hydrocolloid agar agar. The solid
agar material is heated to melt and then cooled to 55 degree C to be poured
gently into the duplicating flask that contains the modified cast. The flask is put
in a shallow container filled with one inch water to allow the agar to cool from
the bottom upwards (compensation for gelation shrinkage).
   This duplication is essential to:
   A) The stone of the master cast can not withstand the high temperature
during casting.
   B) The stone cast will not allow thermal or hygroscopic expansion to
compensate for casting shrinkage.
   C) The stone material is not porous and will not allow for gas to escape
during burnout of the wax pattern.
   Duplicating flask is metal case that consists of:
        a)Bottom.
        b)Ring.
           c)Feeding top.
        Ticoniurn duplicating flask is used because of its simple design and
reliability in controlling shrinkage.

                                                    1- Ticoniurn duplicating flask is
                                                       used because of its simple de-
                                                       sign and reliability in
                                                       controlling shrinkage.




                                                                       Mostafa Fayad 7
                                                                 LABORATORY PROCEDURES




                                                 3- After setting of the colloid material,
2- Securing the master cast to the base of the
                                                    remove the base of the flask and retrieve
   duplicator with clay or utility wax. After
                                                    the master cast by prying with two plaster
   placing the pouring reservoir, flow the
                                                    knives where the clay or wax is placed
   melted colloid.
                                                    for stability.




4-Mix the investment material.                   5- Pouring of the refractory material in the
                                                    mold.




6- Break the hydrocolloid away from the          7- Drying the refractory cast.
    cast.




8- Immersing the refractory cast into            9- Cooling the dipped wax on absorbent
    molten bees wax, to provide sealing.             paper.




                                                                                  Mostafa Fayad 8
                                                LABORATORY PROCEDURES


Refractory cast is a cast made of material that will withstand high
     temperature without disintegration and when used in partial denture
     casting, has expansion to compensate for metal shrinkage.

Duplicating colloids are capable of being re-used many times. They must
    be cleaned and melted after each use. They may be prepared and
    stored in automatic duplicating machine. If this machine is not
    available, a double boiler can be used to prepare the colloid for
    duplication.
            The clean colloid can be cut into small pieces and re-heated
    in this double boiler to a fluid consistency. When cooled to working
    temperature, it will be cool enough to flow easily without melting
    the blockout wax. A 630C is a suitable working temperature.

Investment material is used for making the refractory cast. The type of
     investment depends on the type of the alloy used.

                Gypsum-bounded investment is used for low heat alloys
        (Type IV Gold + Ticonium)
                phosphate-bound investment is used for high heat alloys
        (vitallium and nobilium). A special liquid is needed with
        phosphate-bonded investment.

             Investment materials must be measured and mixed accurately
     according to the manufacturer instructions, to ensure that the
     expansion of the metal during burnout will match the shrinkage of
     the alloy.
             When the refractory material has completely set, the cast is
     removed from the colloid mold and placed in drying oven at 180 –
     200o F for half to one hour. The cast is then either dipped into bees
     wax at 280 - 300 0F for 15 seconds or sprayed while it is still warm .

 Spraying the cast is done for the following purposes:
  - To provide a smooth and dense surface.
  - To allow for better adherence of the wax or plastic patterns.
  - To prevent scratches of the cast.
  -




                                                             Mostafa Fayad 9
                                                   LABORATORY PROCEDURES



9- Waxing the framework on the refractory cast:
    Design transfer: Before the actual waxing can begin• the design must
       once again be drawn by transferring from master cast.
    Materials: Waxing the framework is done by contouring wax, preformed
        wax patterns or preformed plastic patterns to form the pattern of the
        removable partial denture framework. These patterns have almost
        replaced freehand waxing.
    Wax pattern specifications for partial denture components:




                                                               Mostafa Fayad 10
                                                          LABORATORY PROCEDURES



  10- Sprueing the Framework:
          Sprueing: It is the process by which wax, metal or plastic form sprues
  are attached to the wax pattern, to provide an entrance or pathway channel to
  the mold space and to serve as a reservoir of metal during casting procedure.
          There are certain general basic principles which should be followed:
      1 It should be attached to the most bulky portion of the wax pattern.
      2 The thickness of the sprue should be larger than that of thickest part of
      the wax pattern
      3 The diameter of the sprues should increase gradually from inside
      outward.
      4 The pathway should be smooth and direct. No sharp angles are allowed
      throughout the course of the spure.
      5 Reinforce all junctions with additional wax to act as reservoirs and
      avoid constrictions
       Types of Sprueing:
1- Single Sprueing (horizontal Sprueing): it has a limited application• it is used
   in small castings.
2- Multiple Sprueing: Is used in big castings and has three forms:
              a- Top (direct) Sprueing.
              b- Inverted( bottom- indirect) Sprueing.
              c- Horizontal (rear)Sprueing.


       1) Top Sprueing
                 It consists of the sprue originating from the top of the wax
             pattern.The sprue has a diameter of a pencil, it consists of a main
              wide central sprue from which narrower auxiliary sprues run to each
              corner of the wax pattern. Done for majority of maxillary cases.
       2) Inverted Sprueing:
                   In which the base of the refractory cast should have a hole in
              its center. A cone-shaped metal sprue of suitable size is placed into
              the hole. Auxiliary sprues are then placed between the main sprue
              and the thick sections of the wax pattern.




                                                                       Mostafa Fayad 11
                                                     LABORATORY PROCEDURES


                By this method of Sprueing, contraction of the metal during
           cooling tends to pull the casting towards the model rather than away
           from it. Done for majority of mandibular cases
    3) Horizontal Sprueing:
         In which sprueing is from the posterior edge of the casting. Used
           with complete cast palatal major connector




      Single Sprueing.                           Inverted Sprueing




A central hole prepared to receive the       Horizontal Sprued pattern.
central sprue.


11- Investing the sprued pattern:
       Casting investment is a process of covering or enveloping of the sprued
 wax pattern by an investment material before casting. It is performed in order
 to enclose a mold resulting from the burn-out of the pattern.
      When the wax pattern and sprues are burned out, a space will be created
 where a molten metal is forced to take the same shape of that pattern.


      Investing a partial denture wax pattern therefore consists of two
 components:
 a) The refractory investment cast upon which, the wax pattern has been
 performed




                                                                     Mostafa Fayad 12
                                                           LABORATORY PROCEDURES



b) The outer cast investment surrounding the cast and pattern. This portion is
confined by a ring (cylinder), winch is made of metal. The ring will not be
removed till the end of casting procedure. It should be lined with a wet layer
of cellulose to allow for both setting and thermal expansion of the investment.




    Investment provides the following purposes
1- Strength necessary to hold forces exerted by the entering stream of
molten metal until solidification of the metal occurs.
2- Smooth surface for the mold cavity so that the final casting will require
as little finishing as possible.
3- An avenue of escape for most of the gases entrapped in the mold cavity
by the entering stream of molten metal.
4- Investment together with other factors provide necessary compensation
for contraction of the metal from the molten to the solid State.


   Casting investment material!!
  It is a refractory material in which the mold is made!
  Gypsum bonded casting investment material!
  ! This material can be used for casting gold alloys
  ! The expansion of the mold counteracts the casting shrinkage gold alloys!
  ! It can be burnt out at 7040C (13000F) without breakdown!
  Phosphate -Bonded Casting Investment Material!
  ! This material is used for casting chromium-cobalt alloys.
     It can!counteract the casting shrinkage of chrome cobalt alloys!
     It can be burnt out to 10370 C without breakdown.




  Technique of Investing the Refractory Cast:
      1) Line the investment ring with one layer of strip substitute asbestos.
           Leave about 7 mm short of sprue end.


                                                                        Mostafa Fayad 13
                                                          LABORATORY PROCEDURES


         2) The refractory cast is dipped into slurry water to moisten its
            surface. This wetting keeps the dry cast from taking up water from
            the investment material mix.
         3) Mix Investment and distilled water according to the manufacturer’s
            instructions. Al-ways add powder to water.
         4) Investment mix is applied in two coats (two-part mold):
         a) First Coat (3 to 4 mm) painted on to ensure that no air bubbles are
            trapped.
         b) Second Coat: After the initial set of the paint on . The investment
            mix is poured into the investment ring around the pattern. The cast
            should be centered in the ring with at least 1/4 inch from the sides
            of the ring.


REMENBER

        - The investment ring is lined with one layer of asbestos casting ring
liner. The liner should be 6:7 mm shorter than the ring at the crucible end to
act as a lock against investment rotation inside the ring. The asbestos
permits for the escape of hot gases and allows space for investment
expansion.
      - The refractory cast is dipped in slurry water to moisten its surface
and to prevent it from absorbing water from the investment material.
       - The pattern is painted with a wetting agent to allow the outer
investment to adhere to the pattern.


                                                          Top Ring


                                                          Asbestos Substitute


                                                          ¼   inch    clearance    of
                                                          Asbestos Substitute


                             Investing the wax pattern.




                                                                       Mostafa Fayad 14
                                                        LABORATORY PROCEDURES



    12-Burnout of the wax pattern:
               It is the elimination of the wax by heat of the invested pattern to
          prepare the mold to receive the molten metal.


       The burn out procedures serves the following functions:
        Dries the investment (Driving off moisture from the mold)
        Burning , vaporization and elimination of the wax pattern, thus leaving a
         cavity.
        Thermal expansion of the mold to compensate for contraction of the
         metal on cooling (solidification).


                The investment is placed in the burn out furnace with the sprue
          hole downwards. The investment should be moist before starting the
          burn out cycle to allow the investment to heat uniformly.
                The burnout should start in a cold oven, and then the temperature
          should be slowly increased to 12500F over a period of two hours. This
          temperature is maintained for half an hour (heat soaking).
                 The time and temperature required to eliminate the wax should
          be according to the Manufacturer’s instructions.
-         Burnout furnaces are either electric or gas and must be vented to allow
    the noxious fumes that result from the burnout, to escape the work area.
    Modem furnaces are controlled electronically to permit time/temperature
    relationship to be set exactly to the alloy manufacturers specifications. With
    these modern furnaces, over and under-heating are avoided.


    13- Casting the partial denture framework:
          Casting is to produce an object in a mold.
          Mold is a cavity in which metal is cast.
          Crucible is a container made of porcelain used for melting metal. It
              sustains high degrees of temperature.
          Casting Procedure:
                       The method of casting will vary according to the alloy and
                equipment used. All methods use force to inject the molten alloy
                quickly into the mold cavity. This force is usually centrifugal.


                                                                    Mostafa Fayad 15
                                                      LABORATORY PROCEDURES


                    Molten metal is faced into the pre-heated mold by the use
             of centrifugal force casting material. Heat and force to the metal
             during casting are critical.
                 Heat applied to melt the metal may be applied by a blowtorch
           using gas and air, gas and oxygen, acetylene, electrical conduction,
           or induction.


      Recovering the Casting:
               When the casting step is completed, the mold is removed
           from the machine and allowed to cool according to the
           manufacturer’s instructions. The outer layer of the investment is
           broken off by tapping it with a wooden mallet or a hammer.
                The first layer of investment is then removed by stiff brush
           under running water. Sandblasting machine is used to remove any
           remaining investment. The casting can now be examined for de-
           fects.


14- Finishing and polishing of the framework:

      Finishing the framework; is to refine its surface. It is accomplished by
           cutting the sprues carefully using separating disks and grinding off
           excess metal flashes by suitable stones Rubber abrasive wheels,
           disks and points are used to refine the surface.


      The following precautions should be maintained
           1- Avoid overheating of the framework by continuously soaking it
              in cold water. Overheating may cause warpage of the casting.
           2- Avoid undue pressure to the sprues or the casting. This is
              accomplished by using high speed hand piece.


      Polishing the framework
                   It is making its surface smooth and glossy. Polishing is
             accomplished first by smoothing the surface of the casting by
             coarse disks and stones, followed by finer forms. Final polish is


                                                                 Mostafa Fayad 16
                                                    LABORATORY PROCEDURES


             attained by polishing compounds on felt wheels and high speed
             lathe in chrome cobalt castings and by rouge on felt wheels for
             gold castings.

      Finishing and polishing chrome cobalt castings should be done with
           special high speed equipments (sand blasting and electrolytic
           polishing).


      Hard heat treatment of gold castings
                When the gold casting has been quenched in water, it is
          removed from the investment in a soft and most ductile condition.
          All grinding and finishing operations are performed while it is in
           this condition. After finishing and just before final polishing, it
           should be heat hardened as follows:

              1.Stabilize the furnace at the desired temperature 600-7000F for
                 yellow gold castings and 800o F for white gold alloys.
              2.Place the casting on a metal tray in the furnace and allow to
                 heat soak for l5 minutes.
              3.Remove the tray with the casting and leave it to bench cool.
                 Heat treatment will produce from 85% to 100% of the
              strength of gold casting and will prevent the possibility of
              warpage.


                 N.B.: Chrome cobalt alloys cannot be heat hardened. They
              originally have satisfactory physical properties.


15- Fitting the framework to the cast:
         The casting is checked for accuracy on the master cast. Any
    point of interference should be ground until the casting fits properly
    on the cast. The casting is now ready for try-in in the patient’s
    mouth.


16- Processing of acrylic resin
             The acrylic is processed in the conventional manner.


                                                                Mostafa Fayad 17
                          LABORATORY PROCEDURES




!!              !!




          !!
                     !!




           !!
                     !!




     !!




                                   Mostafa Fayad 18
                                                                       LABORATORY PROCEDURES




            CLINICAL AND LABORATORY PROCEDURES
                   FOR RPD CONSTRUCTION
                  Clinical procedures                                  Laboratory procedures

1-    Diagnosis and treatment planning:
     - Extra and intra-oral examinations.
     - X-ray Examinations.
     - Examination of each arch separately.
     - Examination of both arches.
2-    Making primary impression: With an elastic
      material as alginate impression material in a       a- Pouring the impression in stone plaster to
      perforated stock tray.                                   construct a study cast.
                                                          b- Surveying the study cast.
3- Mouth Preparation which includes                       c- construction of the special tray on the study
   a–Conservative,    periodontal      and     surgical        cast.
     treatment.
   b-Preparation of occlusal rest seat, guiding planes
     and probable recontouring of abutments.

4-Making the final impression either with                 d-Pouring the final impression in stone plaster to
A-Alginate impression material in case of tooth                 construct a master cast.
    supported partial dentures.                           e- Surveying the master cast to draw the survey
B-Functional impression in case of tooth and tissue             line on abutment teeth and to determine the
    supported partial dentures.                                 path of placement of the partial denture.
                                                          f- Drawing the design of the partial denture.
                                                          g- Preparation of the master cast for duplication
                                                              1.Blocking the undesirable tooth undercuts in
                                                                wax.
                                                              2.Establishing the relief areas in wax.
                                                              3.C-Making the ledges in wax.
                                                              4.Blocking the tissue undercuts.
                                                          h-Duplication of the master cast into a refractory
                                                                cast (investment cast). This is done by the use
                                                                of agar-agar material in a duplicating flask.
                                                          i- Construction of the wax pattern on dried
                                                                refractory cast.
                                                          j-Spruing, investing, wax elimination (burn out)
                                                                and casting in metal (gold or Chrome cobalt
                                                                alloy)
                                                          K-Pickling, finishing and polishing the metal
5-Testing the framework on the master cast and then             framework.
     try in of the metal in the patient’s mouth.

6- Functional impression with framework in mouth
     in distal extension partial denture cases.           l-Pouring of the functional impression, and
                                                               construction of wax blocks.
7- Jaw relation registration and tooth selection.
                                                          m-Mounting the cast on an articulator and setting-
                                                             up of artificial teeth
8- Try-in of the waxed partial denture.
                                                          n- Flasking and Processing in acrylic resin.
9- Delivery and final adjustment.                         o- Finishing and polishing the acrylic denture.
10-Periodic check-up and relining when necessary.




                                                                                       Mostafa Fayad 19
                                                Diagnosis of partially edentulous patients


                 EXAMINATION, DIAGNOSIS

               AND TREATMENT PLANNING

Objectives of any prosthodontic treatment:
(1) The elimination of disease;

(2) The preservation, restoration, and maintenance of the health of the
remaining teeth and oral tissues (which will enhance the removable partial
denture design);

(3) The selected replacement of lost teeth for the purpose of restoration of
function in a manner that ensures optimum stability and comfort in an
esthetically pleasing manner.

Indications for a removable in preference to a fixed partial denture

 A. Edentulous areas too long for a fixed prosthesis.

 B. Need to restore soft and hard tissue contours.

 C. Absence of adequate periodontal support.

 D. Structurally or anatomically compromised abutment teeth.

        1. Lack of clinical crown height.

        2. Lack of sound tooth structure.

        3. Unfavorable position, contour or inclination.

 E. Need for cross-arch stabilization. F. Eed for an extension base.

 G. Anterior esthetics.

 H. Physical and emotional problems precluding fixed partial dentures.

 1. Attitude and desires of patient.

 J.   Ease of plaque removal from the natural teeth and partial de ture.




                                                                    Mostafa Fayad 1
                                                   Diagnosis of partially edentulous patients


BASIC CRITERIA FOR PATIENT SELECTION

A.    Acceptable emotional and physical health.

      1.        Basic health observations. 2.       Complete health history.

B.    General physical and mental capacity to tolerate a prosthesis.

     1. Previous number of prostheses. 2.           Physical handicaps.

C.    Degree of patient motivation.

            1. General personal appearance.

            2. Past oral hygiene habits and response to sug¬gested change.

            3. Patient's desire to preserve remaining teeth and surrounding
            structures.

            4. Physical and mental capabilities to augment motivation.

            5. Patient's response to scientific evidence.

D.    Patient's comprehension of pote - tia success or failure of treat¬ment.

E. Types and amounts of drugs or med-ications the patient co sumes
including alcohol and tobacco.

F.    Patient's dietary habits.

G.    Periodontal health.

H.    Oral indices of tissue tolerance.

           Indicate the capacity of supporting structures to resist mechanical
           forces.

           1.    Muco-osseous (ridge) resistance. Bone index of the residual ridge
           (reaction of bone after extraction and ridge loading),

           2.   Dento-alveolar (abutment) resistance. Bone index around the
           abutment teeth (reaction of bone to increased force).

           3.   Soft tissue resistance to biological or mechan¬ical irritation.

I.    Oral manifestations of pathology.

J.    Consultations with other medical and dental specialists.


                                                                       Mostafa Fayad 2
                                               Diagnosis of partially edentulous patients


PURPOSE AND UNIQUENESS OF TREATMENT

        The purpose of dental treatment is to respond to a patient's needs.
Although there are similarities between partially edentulous patients,
significant differences exist making each patient, and treatment, unique.

       The delineation of each patient's uniqueness occurs through the patient
interview and diagnostic clinical examination process. This includes four
distinct processes:

(1) Understanding the patient's desires or chief concerns/complaints regarding
their condition (including its history) through a systematic interview process.

(2) Ascertaining the patient's dental needs through a diagnostic clinical exam.

(3) Developing a treatment plan that reflects the best management of the
desires and needs (unique to their medical condition or oral environment).

(4) Appropriately sequenced execution of the treatment with planned follow
up.

Complex treatment planning often requires two appointments.

The first appointment includes

    a preliminary oral examination (to determine the need for management
     of acute needs),

    a prophylaxis,

    full-mouth radiographs,

    diagnostic casts, and

    Mounting records if baseplates are not required.

The follow-up appointment includes

    mounting of the diagnostic casts (when baseplates and occlusion rims
     are needed),

    a definitive oral evaluation,

    review of the radiographs to augment and correlate with clinical
     findings,

    arrangement of additional consultations where required,

                                                                   Mostafa Fayad 3
                                                Diagnosis of partially edentulous patients


I- FIRST DIAGNOSTIC APPOINTMENT

      A. Patient interview:

      B. Cursory (initial) examination

      C. Oral prophylaxis

      D. Collecting diagnostic data: • Photography • Radiography • Casts

II-SECOND DIAGNOSTIC APPOINTMENT

      A-Definitive oral examination:

      B-Radiographic survey

      C-Analysis of mounted diagnostic casts:

      D. Consultation requests:

      E. Development of treatment plane.

III-TREATMENT PLANE IN RPD




Prosthodontic Diagnostic Index ( PDI ): see classification

The American College of Prosthodontists (ACP) has developed a classifi cation
system for partial edentulism based on diagnostic findings.




                                                                    Mostafa Fayad 4
                                                Diagnosis of partially edentulous patients


A ] PATIENT INTERVIEW

1- Structure of interview:

      HISTORY TAKING

  1.Personal history                            5.Frequency of dent examinations.

  2.Chief complaint                             6.Previous dental treatment.

  3.Phy health and medical history.             7. Habits and type of Diet.

  4.Psychological health.                       8. Patient expectations

2- Objectives:

       a. Establishing of a rapport:

       We should meet the mind of the patient before we meet his mouth.

       b. Gaining insight into the psychological makeup of the patient
     (patient attitude):

       De Van stated, "Meet the mind of the patient before meeting the mouth
     of the patient". Hence, we understand that the patient's attitudes and
     opinions can influence the outcome of the treatment.

          Dr. MM House proposed the first one in 1950, which is widely
       followed. House's Classification Based on patient’s mental attitude,

                  The philosophical patients. (Well adjusted and easygoing)

               The exacting patients. (Precise in everything they do)

               The hysterical patients. (Are emotionally unstable and

               convinced that they will never be able to wear a prosthesis)

               The indifferent patients. (are uncooperative)



                                                                    Mostafa Fayad 5
                                                   Diagnosis of partially edentulous patients


         c. Evaluating the systemic disturbances that may affect the
       patient’s treatment:

               These systemic disturbances include the following:

                Diabetes                                      Pemphigus vulgaris

                Arthritis                                     Epilepsy

                Paget’s disease                               Cardiovascular diseases

                Acromegaly                                    Cancer

                Parkinson’s disease                           Transmissible diseases

       Systemic disturbances that can have a significant effect on the treatment
of the patient include the following:
    Diabetes: multiple small abscesses and poor tissue tone frequently
        accompany uncontrolled diabetes. The diabetic patient often has
        excessive rate of bone resorption, hence, frequent relining may be
        necessary. And reduced salivary output, which significantly reduced the
        ability of patient to wear prosthesis with comfort, and increases the
        possibility that caries will occur.
    Vitamin deficiency which cause inflammation and bleeding of the
        gingiva and fissures in the corners of the mouth.
    Oral Malignancies: The most common oral complications of radiation
        and chemotherapy for malignancies are mucosal irritation, xerostomia
        and bacterial and fungal infections. Tissues having bronze colour and
        loss of tonicity are not suitable for denture support. Once the dentures
        are constructed, the tissues should be examined frequently for
        radionecrosis.
       Blood disease e.g. anemia; patients have pale mucosa, sore and red
        tongue and gingival bleeding.
    Transmissible diseases; e. g. hepatitis and tuberculosis pose a
        particular hazard for the dentist, patients and dental auxiliaries.

                                                                       Mostafa Fayad 6
                                             Diagnosis of partially edentulous patients


 Diseases of the Joints: patients with osteoarthritis affecting the finger
   joints may find it difficult to insert and clean dentures. With limited
   mouth opening and painful movements of the jaw, it becomes necessary
   to use special impression trays. It may also become necessary to repeat
   jaw relations and make post-insertion occlusal adjustments due to
   changes in the joint.

 Cardiovascular Diseases: Cardiac patients will require shorter
   appointments.

 Diseases of the Skin: Skin diseases like Pemphigus have oral
   manifestations, which vary, from ulcers to bullae. Such painful
   conditions make the denture use impossible without medical treatment.

 Neurological Disorders: Diseases such as Bell's palsy and Parkinson's
   disease can influence denture retention and jaw relation records. Add
   sufficient bulk to buccal surface contour of maxillary RPD to support
   flaccid muscles.
 Climacteric Conditions :Climacteric conditions like menopause can
   cause Tendency to gag, burning sensation, xerostomia, vagueareas of
   pain, taste alterations , glandular changes, osteoporosis and psychiatric
   changes in the patient.
 Pernicious anaemia :       Xerostomia , disturbance of taste sensation,
   Susceptibility to denture trauma.
 Chronic pulmonary disease : Shortness of breath,wheezing, increased
   respiratory rate, persistent cough and Occlusal vertical dimension is
   difficult to record because of patient ’ s tendency to mouth breathe.
 Salivary gland disorders : Xerostomia, painful and burning mucosa




    d . Evaluating the drugs that can affect prosthodontic treatment:



                                                                 Mostafa Fayad 7
                                          Diagnosis of partially edentulous patients


           These drugs include the following:

           *Anticoagulants

           *Antihypertensive agents: cause decrease in salivary flow

           *Endocrine therapy: cause sore mouth and discomfort

           *Saliva-inhibiting drugs

           *Dilantine: cause gingival enlargement

  e. Dental history:

      The cause of teeth loss: If the teeth were lost because of caries,
        special emphasis will have to be placed on oral hygiene
        procedures. If the teeth were lost because of periodontal disease,
        every effort must be made to discover and eliminate its cause.

      If a removable partial denture has been constructed previously for
        the patient, it is important to learn as much as possible about the
        patient' experience during and following treatment.

      Expectation of treatment: If the patient has unrealistic expectation
        e.g. a removable partial denture without major connector crossing
        the palate) the patient expectation should be changed through
        education.

      Chewing habits: The patient is asked about the preferred and non
        preferred side for chewing. This will determine the amount of
        support, retention and bracing of the denture on each side.

      Para functional habits: clinching and bruxism has adverse effect
        on the denture supporting structures.

f. Ascertaining patient’s expectations of treatment, assessment of
patient motivation and attitudes towards dentures:


                                                              Mostafa Fayad 8
                                                   Diagnosis of partially edentulous patients


      The patient's attitudes and psychological status of the patient have
   considerable influence on the success of the treatment.

3- Obstacles:

      a. From the dentist:

                   Not listening to the patient

                   Choicing words misunderstanding by the patient

                 Failure to use the obtained information in the treatment of the
                    patient

      b. From the patient:

           - Fearful of his condition       - Lack of response

4- Aids for successful interview:

     1. Dentist attitude and behaviour      2. Phrasing of questions

         INFECTION CONTROL

         Recommended Infection Control Practices for Dental Treatment

          Gloves should be worn in treating all patients.

          Masks should be worn to protect oral and nasal mucosa from
            splatter of blood and saliva.

          Eyes should be protected with some type of covering to protect
            from splatter of blood and saliva.

          Sterilization methods known to kill all life forms should be used
            on dental instruments. Sterilization equipment includes steam
            autoclave, dry heat oven, chemical vapor sterilizers, and chemical
            sterilants.



                                                                       Mostafa Fayad 9
                                                  Diagnosis of partially edentulous patients


           Attention should be given to cleanup of instruments and surfaces
               in the operatory. This includes scrubbing with detergent solutions
               and wiping down surfaces with iodine or chlorine (diluted
               household bleach solutions).

           Contaminated disposable materials should be handled carefully
               and discarded in plastic bags to minimize human contact. Sharp
               items, such as needles and scalpel blades, should be contained in
               puncture-resistant containers before disposal in the plastic bags.

B] Clinical examination

      PATIENT EVALUATION

      • Gait : People with neuromuscular disorders show a different gait.
         Such patients will have difficulty in adapting to the denture.

      • Age : patients belonging to the fourth decade of life will have good
         healing abilities and patients above the sixth decade will have
         compro¬mised healing.

      • Sex : Male patients are generally busy people whoappear indifferent
         treatment. They are only bothered about comfort and nothing else.On
         the other hand, female patients are more critical about aesthetics

      • Complexion and Personality : Evaluating the complexion helps to
         determine the shade of the teeth. Executives require smaller teeth.

      • Cosmetic Index : It basically speaks about the aesthetic expectations
         of the patient. Based on the cosmetic index, patients can be classified
         as:

                          Class I: High cosmetic index. They are more
                            concerned about the treatment and wonder if their
                            expectations can be fulfilled.



                                                                     Mostafa Fayad 10
                                                      Diagnosis of partially edentulous patients


                              Class II: Moderate cosmetic patients. They are
                                patients with nominal expectations.

                              Class III: Low cosmetic index. These patients are not
                                bothered about treatment and the aes-thetics. It is
                                very difficult for the dentist to know if the patient is
                                satisfied with the treatment or not.

       Extraoral examination

        o   Facial examination:                        o    Lip Examination

                        Facial Form                   o    TMJ Examination

                        Facial Features               o    Neuromuscular
                                                            Examination
        o   Muscle Tone
                                                                        Speech
        o   Muscle Development
                                                                        Co-ordination
        o   Complexion



      a-Facial Features :If the face appears collapsed, it indicates the loss of
      vertical dimension (VD). Decreased VD produces wrinkles around the
      mouth. Excessive VD will cause the facial tissues to appear stretched.

      b. Complexion :The colour of the eye, hair and the skin guide the selection
      of artificial teeth.




    Oral Examination

         A complete oral examination should precede any treatment decision. It
should include a visual and digital evaluation of the teeth and surrounding tissue

            Sequence for Oral Examination


                                                                         Mostafa Fayad 11
                                                     Diagnosis of partially edentulous patients


             An oral examination should be accomplished in the following
             sequence:

              visual examination,

              pain relief and temporary restorations,

              oral prophylaxis,

              radiographs,

              evaluation of teeth and periodontium,

              vitality tests of individual teeth,

              determination of the floor of the mouth position,

              and impressions of each arch.




      Relief of pain and discomfort and placement of temporary
         restorations
                management of acute needs

                relieve discomfort arising from tooth defects

                Determine as early as possible the extent of caries and to arrest
                 further caries activity.

         By restoring tooth contours with temporary restorations, the impression
will not be torn on removal from the mouth, and a more accurate diagnostic cast
may be obtained.

      A Thorough and Complete Oral Prophylaxis

An adequate examination can be accomplished best with the teeth free of
accumulated calculus and debris. Also, accurate diagnostic casts of the dental


                                                                        Mostafa Fayad 12
                                                       Diagnosis of partially edentulous patients


arches can be obtained only if the teeth are clean; otherwise the teeth reproduced
on the diagnostic casts are not a true representation of tooth and gingival contours.

         Cursory examination may precede an oral prophylaxis, but a complete
oral examination should be deferred until the teeth have been thoroughly cleaned.




    Initial (Cursory) oral examination

Objective:

     1. Detection of problems requiring immediate attention

     2. Evaluation of oral hygiene

     3. Evaluation of caries susceptibility

     4. Detection of oroantral or oronasal communications

     5. Assessment of applied forces

                   1.   Opposing occlusion.

                   2.   Muscular force and elevator muscle development.

                   3.   Parafunctional habits.

                            a. Clenching.      b. Bruxism

                   4.   Length of edentulous span.

                   5.   History of prosthesis failure.

                            a. Solder joint failure.        b. Porcelain failure.

                            c. Fractured RPD components.

        6. History of poor tissue tolerance.

                            a. Chronic sore spots.


                                                                          Mostafa Fayad 13
                                                 Diagnosis of partially edentulous patients


                         b. Excessive bone resorption.

                         c. Abutment tooth mobility.

                         d. Fracture or attrition of natural teeth.

                         e. Attrition, abrasion, erosion, abfraction




 Definitive visual oral examination:

Complete oral examination to evaluate the following:

A] The teeth and periodontium:

1. Caries and existing restorations: All carious teeth must be restored prior to
starting definitive prosthodontic treatment,

2. Pulp to detect pulpitis or pulp necrosis

3. Sensitivity to percussion

4. Mobility and C/R ratio: The degree of mobility of all teeth should be
recorded using a scale commonly used for classifying mobility:

     ■ Class 1: A tooth demonstrates greater than normal movement, but less
     than 1 mm of movement in any direction.

     ■ Class 2: A tooth moves 1 mm from normal position in any direction.

     ■ Class 3: A tooth moves more than 2 mm in any direction, including
     rotation or depression. A change from normal physiologic movement may
     indicate traumatic occlusion or periodontal disease. Teeth exhibiting
     Class 3 mobility have a poor prognosis and usually will require
     extraction.

       Causes:

                  Trauma from occlusion

                                                                      Mostafa Fayad 14
                                                   Diagnosis of partially edentulous patients


                  Inflammatory changes of the PDL

                  Loss of alveolar bone support

      Treatment:

                  Scaling

             Learning and ascertaining good oral hygiene

             Splinting when:

                    • All the remaining teeth have reduced support

                    • Only two or three widely spaced retainable teeth

                    • The first premolar and all molars have been lost and the
                    second premolar is to serve as the abutment

5. Periodontium:

       The health of the PDL is determined by findings that need periodontal
       treatment are:

      1. Pocket depth in excess of 3 mm

      2. Furcation involvement

      3. Deviations from normal colour and contour in gingiva indicating
      gingivitis

      4. Marginal exudate

      5. Less than 2 mm of attached gingiva

      6. Pulling of muscle or frena on attached gingiva




                                                                      Mostafa Fayad 15
                                                 Diagnosis of partially edentulous patients


B] . Oral mucosa:

            Pathologic changes

            Tissue reactions to the wearing of old prosthesis:

            Soft tissue displacement

            Palatal papillary hyperplasia: It is associated most often with a
              poorly fitting prosthesis that has been worn for a prolonged
              periods. It consists of numerous small papillary growths.

            Epulis fissuratum: It is a tumour like hyper plastic growth in the
              sulcus caused by an ill- fitting or overextended border of a
              removable prosthesis.

            Denture stomatitis: It is characterized by generalized
              erythematic for all the tissues covered by the prosthesis.
              Candida albicans has been shown to be present in much higher
              percentage of denture stomatitis. Traumatic occlusion, poor fit
              of the prosthesis, poor oral hygiene and continuous wearing of
              the prosthesis have all been suggested as contributing factors to
              this condition.

C]. Hard tissue abnormalities:

    Torus palatinus: Removal of a torus palatinus is not usually necessary; a
      major connector can be designed to circumvent the torus.
    Torus mandibular. It is exostoses, usually occurring bilaterally on the
      lingual surface of the body of the mandible.
    Undercuts and bulbous maxillary tuberosities:
         The effect of some undercut areas may be minimized by:
         o Change in the path of insertion of the RPD in case of unilateral undercut.

                                                                    Mostafa Fayad 16
                                                  Diagnosis of partially edentulous patients


          o Relieving the denture base or reducing the length of the denture border
           o Surgical correction of undercuts.
           o Flexible denture base or flexible border
           o Reduce length of denture border
    The mylohyoid ridge: Some of these ridges are felt to be
       pronounced and the soft tissue covering is thin and is easily
       traumatized by insertion and removal of prosthesis.
D]. Soft tissue abnormalities:

    Labial frenum: If the frenum is attached highly at the crest of the
       ridge, or it was bulky, the notch in the maxillary denture should be
       done to accommodate this frenum shape and position.
    Lingual frenum: It can greatly compromise the rigidity and
       adjustement of the major connector.
    Flabby gingiva: Atrophy of the residual ridge does occur
       occasionally, and the gingiva loses its bony support and becomes
       freely, Tnis area should be evaluated to determine whether it requires
       conservative treatment or surgical removal.
 Tongue size & mobility: The tongue should be examined for :
      • Size: Presence of a large tongue decreases the stability of lower
      denture and ate also a hindrance to impression making. Tongue-biting is
      common after insertion of the denture. A small tongue does not provide
      adequate lingual peripheral seal.
      •   Movement and coordination: Tongue movements and coordination
      are important to register a good peripheral tracing. They are also
      necessary in maintaining the denture in the mouth during functional
      activities like speech, deglutition and mastication, etc.

E] Occlusal relationships:

    It is the relation between the opposing teeth and between the teeth and

                                                                     Mostafa Fayad 17
                                               Diagnosis of partially edentulous patients


the opposing ridge is examined for.
 a- Available interarch space for placement of artificial teeth.
 b- The degree of anterior vertical overlap.
 c- Super eruption and tilting of the remaining teeth.
d- Cuspal interference.

F] - Temporomandibular joint (TMJ) examination:
TMJ disorders   can be detected by one or more of the following signs:
  a- Reduced inter incisal opening (Normal maximum opening is 55mm +
   15mm).
  b- Pain and tenderness over the TMJ at rest and during movement.
  C- Clicking during opening and closing.
  d- Midline deviation during wide opening.
  e- Muscle pain and tenderness.
  f- Headache and ear pain.
G]. Quality and quantity of saliva:

         Dry mouth >>>> no lubricating effect >>>> saliva substitute

         Thick and ropy saliva or copious amounts of serous saliva

        >>>> problems during impression.

        Thick ropy saliva alters the seat of the denture because of its tendency
        to accumulate between the tissue and the denture. Thin serous saliva
        does not produce such effects.

        Xerostomic patients show poor retention and excessive tissue
        irritation whereas excessive salivation complicates the clinical
        procedures. use of synthetic saliva, with a carboxymethyl cellulose
        base, which can be enriched with fluoride in an effort to counteract
        caries. Frequent use provides an excellent means of maintaining high



                                                                   Mostafa Fayad 18
                                                   Diagnosis of partially edentulous patients


        fluoride intraorally for long periods of time, thus enhancing the
        remineralization of incipient caries.

H] . Space for mandibular major connector:

              The superior margin of the connector should be located 3 mm
                below the free gingival margins of the mandibular teeth >>>>>
                to avoid damage to the gingival tissues.

              The inferior border of the connector should be positioned at or
                slightly above the position of the active floor of the mouth
                >>>>> to prevent interference with the functional movements
                of the floor of the mouth and to help avoid the packing of food
                under the major connector.

              A minimum of 7 to 8 mm. of space should be available if a
                lingual bar major connector is to be used. Available space is
                measured with a calibrated periodontal probe (William's
                probe) , while the patient raising the tongue toward the palate.
                Measurements are made at several positions; the probe is then
                used to transfer it to the cast.


I] Oral hygiene and caries susceptibility:

    Evaluation of patient's oral hygiene is critical to the prognosis of the
patient's treatment. Disclosing tablets or solution is used to detect plaque,
which will indicate the patient motivation towards oral hygiene.
      The presence of large number of restored teeth, signs of recurrent caries
and evidence of decalcification indicate that the patient is susceptible to caries.
J]. Modification Spaces

          For short spans (<=3 missing teeth), natural tooth, implant-
    supported fixed prostheses, and removable partial dentures can generally
    be considered.
                                                                      Mostafa Fayad 19
                                                                      Diagnosis of partially edentulous patients


                Longer span modification spaces (>=4 missing teeth) present a
      greater       challenge          for     natural        tooth-supported            fixed       prostheses.
      Consequently, the options for treatment are the removable partial denture
      or the implant supported prosthesis.

K] Abutments With Guarded Prognoses

          If the prognosis of an abutment tooth is questionable, or if it becomes
unfavourable during treatment, it might be possible to compensate for its
impending loss by a change in denture design.

          It is sometimes possible to design a removable partial denture so that a
single posterior abutment, about which there is some doubt, can be retained
and used at one end of the tooth-supported base. Then if the posterior abutment
is lost, it could be replaced by adding an extension base to the existing denture
framework. Such an original design must include provisions for future indirect
retention, flexible clasping of the future abutment, and provision for
establishing tissue support.

          Anterior abutments that are considered poor risks may not be so freely
used because of the problems involved in adding a new abutment retainer when
the original one is lost. It is rational that such questionable teeth be condemned
in favor of more suitable abutments, even though the original treatment plan
must be modified accordingly.




          Kennedy Class II, mod I in which molar abutment has a guarded prognosis. Premolar clasp assembly is a
mesial rest, distal guide plane, and wrought wire retainer design that will accommodate future distal extension
movement.




                                                                                              Mostafa Fayad 20
                                                     Diagnosis of partially edentulous patients


  L] Examination of old denture:

  a- the design and quality of construction should be noted and any associated
  problems in relation to gingival and mucosal inflammation or to decalcification
  of contacting tooth surfaces.

  b- It is important to evaluate whether the denture is still fit accurately against
  the teeth and under lying mucosa or not.

C -Radiographic survey:

     1. Complete mouth periapical and bite-wing survey.
     2. Panoramic.
    3. Obtain previous radiographs if possible for purpose of comparison.
  1. Examination of residual ridge to evaluate:

                 All radiolucent and radiopaque areas that vary from normal ranges
                  to determine whether a pathologic condition is present.
                 Root fragments and other foreign bodies to determine whether
                  their removal is indicated.
               Un erupted third molars to determine whether they should be
                  retained or removed.
               Evaluate quantity of bone.
                        oAlveolar.
                        oResidual ridge.
                        oBasal.
         a.        Bone Index (bone factor):
                    The bone factor provides an assessment of the relative response
         of bone to stimulation or irritation. This assessment is made by
         analyzing bone index areas.
                   Bone index areas are those areas of bony support which disclose
         the reaction of bone to increased force, e.g. areas of bone around
         abutment teeth or any other teeth subjected to increased loading.


                                                                        Mostafa Fayad 21
                                             Diagnosis of partially edentulous patients


          These areas are compared to areas of bone around teeth in
  normal function without increased loading.
          A similar consideration may be given to the residual ridge or an
  edentulous area of bone supporting a complete or an extension base
  removable partial denture.
          Evaluation of past response is important in predicting the future
  potential for dento-alveolar (abutment teeth) and muco-osseous (ridge)
  resistance to forces transmitted by an RPD.
          The bone index is difficult to determine from radiographs alone.
  The history of the patient is important in evaluating the rate of
  resorption that may be expected based on previous occurrences. The
  length of time from previous extractions together with morphological
  changes in the residual ridge gives some indication of the host response
  to various forces.

b. Bone Density

Denser bone (more highly mineralized) offers greater resistance to
resorption. The reduced rate of resorption of cortical bone compared to
cancellous bone is likely due to the degree of cellularity and
mineralization, which may influence metabolic activity, as well as to bone
factors. These factors appear to account for the pattern of resorption of the
residual ridges in the edentulous or partially edentulous patient.

   In the mandibular arch the external oblique ridge, the mylohyoid ridge
and the genial tubercles, which are areas of muscle attachments, continue
to resist resorption even when the residual ridge is greatly resorbed.

  The presence of dense cortical bone is often the result of applied forces
arising from ligamentous or muscle attachments which provide tension to
the underlying bone.

c. Extrinsic bone factors. Localized forces applied to bone.


                                                                Mostafa Fayad 22
                                                   Diagnosis of partially edentulous patients


         1.    Pressure-Bone tends to resorb in response to compressive forces.
         The rate of resorption most likely depends on the bone density,
         intrinsic bone factors, and the nature of the applied forces and on the
         interaction of pressure and tension. The remodelling that occurs under
         the extension base of a removable partial denture is an example of
         pressure induced resorption.

         11.   Tension-Bone under tensional stimuli tends to increase in density
         and in some instances may increase in quantity. The lamina dura is a
         response to tensional forces transmitted by the periodontal ligament.
         Orthodontic movement of teeth is a good example of the pressure -
         tension theory. The lamina dura resorbs on the pressure side and bone
         apposition occurs on the opposite side.

     d. Intrinsic bone factors which May influence the rate of resorption.

         Genetic.                                     Pathologic.

         Hormonal.                                    Biochemical.

         Nutritional.                                 Other.

        Wolff’s law of bone physiology-

        Intermittent stimulation can cause bone apposition, constant stimulation
(irritation) causes bone resorption

        Theilmann’s diagonal law of occlusion-

        An interceptive posterior occlusal contact can cause elongation of the
teeth in the arch diagonal to the prematurity

2.    Examination of remaining teeth with special attention focused on
prospective abutments to evaluate:

      The presence and extent of caries and the relation of the carious lesion
        to the dental pulp

                                                                      Mostafa Fayad 23
                                               Diagnosis of partially edentulous patients


 Existing restorations to determine the adequacy of proximal contours
   and the presence of overhanging or deficient margins and recurrent
   caries.
 Root canal fillings: an abutment for a distal extension that is
   endodontically treated carries a greater risk for complications than a
   similar tooth not involved in removable partial denture function.
 Root length, size and form
             Teeth with multiple and divergent roots will resist stresses better
             than teeth with fused and conical roots, because the resultant
             forces are distributed through a greater number of periodontal
             fibers to a larger amount of supporting bone
 C/R ratio: The radiographic crown - root ratio is a commonly used
   index for classifying the degree of existing support for teeth being
   evaluated as probable abutments.
             The length of the tooth occlusal from the crest of the alveolar
   bone is compared with the length of the tooth root apical from the
   alveolar crest, and the comparison is expressed as an approximate ratio.
             A tooth with normal, undiminished alveolar support will have a
   crown - root ratio of approximately 1:2. As a general diagnostic guide, a
   tooth with a crown - root ratio of more than 1:1 is considered to have an
   unfavorable prognosis as an abutment tooth.




 Unerupted third molars: should be considered as prospective future
   abutments to eliminate the need for a distal extension removable partial
   denture
 PDL space: The width of the periodontal ligament around the roots of
   the teeth is of significance in evaluating the stability of the teeth. A thin,
   uniform ligament space is a more favorable sign than is a widened,
   irregular space.


                                                                  Mostafa Fayad 24
                                                     Diagnosis of partially edentulous patients


                Widening in periodontal ligament space: indicate trauma,
                mobility or heavy function
       Lamina dura: The lamina dura is the thin layer of hard cortical bone
         that normally lines the sockets of all teeth. In a roentgenogram, the
         lamina dura is shown as a radiopaque white line around the radiolucent
         dark line that represents the periodontal membrane.
                Uneven lamina dura: During the active tipping process, the
         lamina dura is uneven, with evidence of both pressure and tension on the
         same side of the root. For example, in a mesially tipping lower molar the
         lamina dura will be thinner on the coronal mesial and apicodistal aspects
         and thicker on the apicomesial and coronal distal aspects because the
         axis of rotation is not at the root apex but is above it. The lamina dura on
         the side to which the tooth is sloping becomes uniformly heavier, which
         is nature's reinforcement against abnormal stresses.
                Partial or total absence of lamina dura may be found in
         systemic disorder as: hyperparathyroidism and Paget disease. When
         systemic disease is associated with faulty protein metabolism and when
         the ability to repair is diminished, bone is resorbed and the lamina dura
         is disturbed. Therefore the loading of any abutment tooth must be kept
         to a minimum inasmuch as the patient's future health status and the
         eventualities of aging are unpredictable.
                Thickening of lamina dura : occur if the tooth is mobile , has
         occlusal trauma or is under heavy function.

D] DIAGNOSTIC CASTS

         Impressions should be made for making accurate diagnostic casts to be
mounted for occlusal examination.

         A diagnostic cast should be an accurate reproduction of all the
potential features that aid diagnosis. These include the teeth locations, contours,
and occlusal plane relationship; the residual ridge contour, size, and mucosal
consistency; and the oral anatomy delineating the prosthesis extensions

                                                                        Mostafa Fayad 25
                                                        Diagnosis of partially edentulous patients


(vestibules, retromolar pads, pterygomaxillary notch, hard and/or soft palatal
junction, floor of the mouth, and frena). Additional information provided by
appropriate cast mounting includes occlusal plane orientation and the impact on
the opposing arch; tooth-to-palatal soft tissue relationship and tooth-to-ridge
relationship, both vertically and horizontally.

          A diagnostic cast is usually made of dental stone because of its strength,
and it is less easily abraded than is dental plaster.

  The diagnostic cast impression is usually made with an irreversible
hydrocolloid (alginate) in a stock (perforated or rim lock) impression tray.

  Purposes of accurate diagnostic casts:

        1. Analysis of the contour of hard and soft tissues of the mouth

        2. Preliminary design of the partial denture .Determine of the types of
        restorations to be placed on the abutment teeth

        3. Determine the need for surgical correction of exostoses, frena,
        tuberosities and undercuts

        4. Used to permit a topographic survey of the dental arch that is to be
        restored by means of a removable partial denture and the proposed design
        is drawn on them. To determine the need for mouth preparation including

                (a) Proximal tooth surfaces, which can be made parallel to serve as
                guiding planes;

                (b) Retentive and non retentive areas of the abutment teeth; (c)
                areas of interference to placement and removal; and

                (d) Esthetic effects of the selected path of insertion.

        5. Serve as a plan for the placement of restorations, the recontouring of
        teeth, and the preparation of rest seats.



                                                                           Mostafa Fayad 26
                                                     Diagnosis of partially edentulous patients


       6. Designed casts aid in the presentation of the proposed treatment to the
       patient.

       7. Permitting a view of the occlusion from the lingual and buccal
       aspects.

       8. Individual impression trays may be fabricated on the diagnostic casts

       8. Used as a constant reference as the work progresses. Pencilled marks
       indicating the type of restorations, the areas of tooth surfaces to be
       modified, the location of rests, and the design of the removable partial
       denture framework along with the path of placement and removal, all may
       be recorded on the diagnostic cast for future reference

       9. Diagnostic casts on a suitable articulator permit analysis of:

                     Occlusion,

                   The adequacy of interarch space

                   The presence of over erupted or malposed teeth

                     The presence of tuberosity interferences.

         10. Unaltered diagnostic casts should become a permanent part of the
         patient's record because records of conditions existing before treatment
         are just as important as are preoperative radiographs.

Analysis of mounted diagnostic casts:

  The mounted diagnostic casts provide visual access from all directions and
  enable the dentist to make a detailed analysis of the patient’s occlusion.

      1. Mounting of maxillary cast to articulator

         It is better that the casts be mounted in relation to the axis-orbital
      plane to permit better interpretation of the plane of occlusion in relation to
      the horizontal plane. Although it is true that an axis orbital mounting has

                                                                        Mostafa Fayad 27
                                             Diagnosis of partially edentulous patients


no functional value on a nonarcon instrument because that plane ceases to
exist when opposing casts are separated, the value of such a mounting lies
in the orientation of the casts in occlusion. MAC

2. Jaw Relationship Records for Diagnostic Casts (Vertical dimension of
occlusion and centric jaw relation record)

  One of the first critical decisions that must be made in a removable
partial denture service involves the selection of the horizontal jaw
relationship to which the removable partial denture will be fabricated
(centric relation or the maximum intercuspal position).

  It is recommended that deflective occlusal contacts in the maximum
intercuspal and eccentric positions be corrected as a preventive measure.

         If most natural posterior teeth remain—and if no evidence of
         TMJ disturbances, neuromuscular dysfunction, or periodontal
         disturbances related to occlusal factors exists—the proposed
         restorations   may    safely   be    fabricated     with     maximum
         intercuspation of the remaining teeth. When diagnostic casts are
         hand related by maximum intercuspation for purposes of
         mounting on an articulator, it is essential that three (preferably
         four) positive contacts of opposing posterior teeth are present,
         having wide spread molar contacts on each side of the arch.

         When most natural centric stops are missing, the proposed
         prosthesis should be fabricated so that the maximum intercuspal
         position is in harmony with centric relation. Correction of the
         remaining natural occlusion to create a coincidence of centric
         relation and the maximum intercuspal position is indicated in
         such situations.

         Clinical situation suggest construction of partial denture at centric
         relation:

                                                                Mostafa Fayad 28
                                                    Diagnosis of partially edentulous patients


                   1- Absence of posterior tooth contact

                   2- When all posterior tteeth will be restored with fixed
                   restoration

                   3- Few remaining posterior contacts

                   4- Clinical symptoms of occlusal trauma

                   5- Coincidence of centric jaw relation and maximum
                   intercuspal position

            Materials available for recording centric relation are
            (1) wax;
            (2) modeling plastic;
            (3) quick-setting impression plaster;
            (4) metallic oxide bite registration paste;
            (5) polyether impression materials;
            (6) silicone impression materials.



     3. Inspection of:

             Occlusal plane                           The presence of tuberosity
                                                          interferences
         Occlusion
                                                       interarch space
         Tipped or malposed teeth
                                                       Malrelation of jaws
         Traumatic vertical overlap
                                                       Diagnostic wax up

 Interarch distance

 Lack of sufficient interarch distance for the placement of artificial teeth:

        Caused by



                                                                       Mostafa Fayad 29
                                                   Diagnosis of partially edentulous patients


       A maxillary tuberosity that is too large in vertical height.

       A segment of teeth that has been unopposed for a prolonged period will
         frequently overerupt, carrying the alveolar process with it. Subsequent
         removal of the teeth will produce a situation in which it is impossible to
         establish a functionally and aesthetically acceptable plane of occlusion.

      Management

      The surgical reduction of the vertical height of the tuberosity and at times
   the adjacent residual ridge is necessary if satisfactory replacement of the
   missing teeth is to be accomplished. The area and amount of tissue that should
   be removed can be indicated on the diagnostic east. This provides an excellent
   guide for the oral surgeon or dentist who performs the surgical correction. The
   radiographs are a valuable aid in planning the surgical of fibrous tissue.
   Healing is usually complete in 7 to 10 days. The healing period is extended to 2
   to 5 weeks when bone removal is necessary.

 Maxillary tuberosity interferences.

             The maxillary tuberosity area may be undercut on one or both
             sides.

         The path of insertion of a complete denture can usually be compatible
   with an unilateral tuberosity undercut, but a removable partial denture, with a
   more controlled path of insertion, presents greater problems.

      Management

         The undercut must be evaluated with the aid of the dental surveyor.
   With the cast on the surveying table at the predetermined path of insertion, a
   determination is made as to the amount of relief that will be required in the
   denture if the undercut is not reduced. Moderate to severe tuberosity undercuts
   usually require surgical correction with bone removal.

                bulbous tuberosities

                                                                       Mostafa Fayad 30
                                                     Diagnosis of partially edentulous patients


              Occasionally the tuberosities are so bulbous that the coronoid process
     of the mandible may actually rub against the tuberosity during functional
     movements.

            Management

              Surgical reduction of such a tuberosity is necessary if the patient is to
     wear a removable partial denture.

 Occlusal plane

   1. Irregular occlusal plane: (because extrusion of one or more unopposed
   teeth)

            Management

   Available treatments depend on the degree of extrusion and the condition of the
   tooth:

   • Enameloplasty can effectively reduce a moderately extruded tooth.
   Approximately 2 mm of enamel can be removed in many situations. At times
   the reduction of a single cusp improves the occlusal plane.

   • Placement of an extracoronal cast metallic restoration If the extrusion is
   greater than 2 mm or if the tooth does not lend itself to enameloplasty, The
   degree of reduction is limited as much or more by the clinical crown length of
   the tooth as by the size of the dental pulp.

            The clinical crown length can often be increased by appropriate
   periodontal therapy if crown lengthening is needed to obtain adequate retention
   for the restoration. Useful crown lengthening procedures include tissue
   shrinkage, gingivectomy, apical positioning flaps, and osseous surgery.

   • Endodontic therapy and crown, when sever reduction to be made.

   Extruded teeth can also be repositioned through orthodontic tooth movement
    procedures.

                                                                        Mostafa Fayad 31
                                                Diagnosis of partially edentulous patients


• Severely extruded teeth such as those contacting the opposing ridge present
greater problems. If the alveolar bone has followed the eruption of the
offending tooth, it may be necessary to extract the tooth and remove the
surrounding bone.

• At times endodontic treatment and & drastic reduction of the tooth will enable
it to be used as an overdenture abutment. This treatment can provide valuable
support for a distal extension base. Extruded teeth must always be evaluated
with the occlusal plane in mind.

• Retention of a tooth that will jeopardize the development of a functional and
aesthetic occlusal plane is rarely justified.

2. Malposed occlusal plane: (because of extrusion of an entire segment of an
arch with concomitant drop of the alveolar process):

Extrusion of maxillary molars or premolars, or both, with drop of the alveolar
process till contact the opposing residual ridge, causing obvious space
problems and malposition of the occlusal plane.

       Management

• One approach to treatment is the removal of the extruded teeth in
conjunction with an extensive alveolectomy.

• Consideration should be given to the use of one of the newer orthognathic
surgical procedures. A posterior segmental osteotomy can be effective in
correcting the problem. Close cooperation and communication between the
prosthodontist or dentist and the oral surgeon are essential. Because the dentist
must construct the prosthesis for the postsurgical tooth and ridge relations, he
should determine the ideal position of the segment. The oral surgeon must
determine the procedures and techniques to employ in making the correction.




                                                                   Mostafa Fayad 32
                                                     Diagnosis of partially edentulous patients


          Anterior maxillary osteotomy can also be effective in repositioning the
   anterior teeth and alveolar ridge for patients with severe protrusion of the
   anterior teeth or deep vertical overlap.

 Malrelation of jaws:

   Severe malrelation of the jaws can prevent the restoration of adequate function
   and esthetics.

          Management:

          Several maxillary and mandibular osteotomy procedures are useful in
   correcting these problems. Close cooperation, consultation, and communication
   between the prosthodontist or dentist and the oral surgeon are essential in
   treating patients with malrelation of the jaws.

 Tipped or malposed teeth

          Management:

   • Limited orthodontic procedures for minor tooth movement can be used to
   upright the tipped tooth to allow the placement of an artificial tooth of more
   normal size.

   • Teeth in severe buccoversion or linguoversion should be evaluated. At times
   the removal of the malposed tooth will simplify the design of the prosthesis.

 Traumatic vertical overlap

   Classification:

        Akerly (1977) has classified traumatic vertical overlap into the following
        four basic types:

       Type I -The mandibular incisors extrude and impinge into the palate.

       Type II-The mandibular incisors impinge into the gingival sulci of the
          maxillary incisors.


                                                                        Mostafa Fayad 33
                                                 Diagnosis of partially edentulous patients


    Type Ill-Both maxillary and mandibular incisors incline lingually with
      impingement of the gingival tissues of each arch.

    Type IV-The mandibular incisors move or extrude into the abraded
      lingual surfaces of the maxillary anterior teeth.

Clinical symptoms:

    Abrasion,

    Mobility,

    Migration of the teeth,

    Inflammation and ulceration of the gingiva and oral mucosa.

Management:

  1. Early recognition and treatment with orthodontic or combined
  orthodontic and orthognathic surgery.

  2. Establishing stable occlusal contacts at centric jaw relation

  3. With advanced clinical symptoms, the removal of teeth is indicated.
  Alveolectomy at the time of extraction will help provide space for some
  improvement.

  4. If the teeth are retainable, reduction of the length of the mandibular
  anterior teeth will relieve symptoms temporarily.

  5. A treatment prosthesis that plates the lingual surfaces of the maxillary
  anterior teeth must be used to prevent further extrusion of the mandibular
  incisors until more definitive treatment can be accomplished.

  6. Definitive treatment is based on:

            The degree of horizontal overlap,

            The number and the occlusal relationships of the remaining teeth


                                                                    Mostafa Fayad 34
                                                    Diagnosis of partially edentulous patients


              The health of the supporting structures.

              The need for RPD and its type and location.

           If all the maxillary teeth are present and have healthy support, it may
          be possible to build up the cingula of the anterior teeth with cast
          restorations >>>>> not feasible if the horizontal overlap is too great.

           If a maxillary removable partial denture is indicated, the major
          connector can be extended onto the lingual surfaces of the anterior
          teeth with a thin plate of metal >>>>> a vertical stop to prevent further
          eruption of the mandibular anterior teeth.

           If only a mandibular removable partial denture is required, a lingual
          plate major connector can be designed to prevent continued eruption of
          the anterior teeth. The plating should cover the cingula of the teeth
          with projections extending to the contact points. Rest seats should be
          placed on the canines or first premolars to prevent labially directed
          forces from being applied to the teeth.

    Occlusion

The mounted diagnostic casts are also used for an evaluation of the patient’s
occlusion. The information obtained from the analysis of the occlusion should
be correlated with other clinical findings.

         Occlusal interferences:

Partially edentulous patients have an even greater probability of having
premature occlusal contacts because of the drifting and migration of teeth that
usually accompany the loss of continuity of the dental arch.

         Bruxism:

Severe     bruxism    can   injure   the   teeth,   the    periodontium,       and    the
Temporomandibular joint and may initiate muscle spasm, pain, or discomfort.


                                                                       Mostafa Fayad 35
                                           Diagnosis of partially edentulous patients


The most common causes of bruxism are:

      1. Occlusal interferences between centric jaw relation and centric
      occlusion and

      2. Balancing side contacts.

The clinical symptoms of traumatic occlusion follow:

      • Excessive wear of the teeth, which may include chipping or
      fracture of the teeth.

      • A change in, or a loss of, the supporting structures, which may
      include increased mobility, tooth migration, and pain during and
      after occlusal contact.

      • Involvement of the neuromuscular mechanism of the
      temporomandibular joint, which may include muscle spasm,
      muscle pain, and joint symptoms.

The radiographic signs of traumatic occlusion follow:

      • Widening of the periodontal ligament space with either
      thickening or loss of lamina dura.

      • Periapical or furcation radiolucency.

      • Resorption of alveolar bone.

      • Root resorption.

Management of occlusal interferences and bruxism:

          Occlusal equilibration: it is the selective grinding or coronal
   reshaping of teeth with the intent of equalizing occlusal stress,
   producing simultaneous occlusal contacts, or harmonizing cuspal
   relations.



                                                              Mostafa Fayad 36
                                                   Diagnosis of partially edentulous patients


                    Occlusal equilibration should not be accomplished for every
             patient with occlusal interferences. Many patients have a great
             enough resistive capacity that occlusal forces are not destructive
             regardless of the occlusal relationships of the teeth. If occlusal
             equilibration were accomplished on these individuals, an “occlusal
             sense or continued “awareness of the occlusion” may be developed




E. Consultation requests:




  A. THE PATIENT SHOULD BE MADE AWARE OF THE FOLLOWING.

  1. The nature and severity of the existing dental problems.

  2. Any limitation in function, phonetics, esthetics, and longevity related to the
     prosthesis.

  3. The physical aspects of the prosthesis with regard to bulk and tissue
     coverage.

  4. Any treatment options that may be considered.

  5. The risks, benefits and alternatives related to any treatment plan.

  B . PATIENT MUST UNDERSTAND AND ACCEPT RESPONSIBILITY
  FOR PREVENTIVE HOME CARE AND PROFESSIONAL RECALL.




F. Development of treatment plane:




                                                                      Mostafa Fayad 37
                                              Diagnosis of partially edentulous patients




III-TREATMENT PLANE IN RPD

      Elimination of Infection

      Sources of infection like infected necrotic ulcers, periodontally weak
teeth, and nonvital teeth should be removed. Infective conditions like
candidiasis, herpetic stomatitis, and denture stomatitis should be treated and
cured before commencement of treatment.

      Elimination of Pathology

      Pathologies like cysts and tumours of the jaws should be removed or
treated before complete denture treatment begins. The patient should be
educated about the harmful effects of these conditions and the need for the
removal of these lesions. Some pathologies may involve the entire bone. In
such cases, after surgery, an obturator may have to be placed along with the
complete denture.


                                                                 Mostafa Fayad 38
                                                 Diagnosis of partially edentulous patients


        Preprosthetic Surgery

        Preprosthetic surgical procedures enhance the success of the denture.
Some of the common preprosthetic procedures are:

Labial frenectomy.                         Reduction of genial tubercle.

Lingual frenectomy.                        Reduction of mylohyoid ridge.

Excision of denture granulomas.            Excision of tori.

Excision of flabby tissue.                 Vestibuloplasty.

Reduction of enlarged tuberosity.          Lowering the mental foramen.

Alveoloplasty.                             Ridge augmentation procedures.

Alveolectomy                               Implants




        Tissue Conditioning

        The patient should be requested to stop wearing the previous denture for
at least 72 hours before commencing treatment. He/she should be taught to
massage the oral mucosa regularly.

        Special procedures should be done in patients who have adverse tissue
reactions to the denture. Denture relining material should be applied on the
tissue side of the denture to avoid denture irritation. Treatment dentures or
acrylic templates can be prepared to carry tissue-conditioning material during
the treatment of abused tissues.

        Nutritional Counseling

        Nutritional counseling is a very important step in the treatment plan of a
complete denture. Patients showing deficiency of particular minerals and


                                                                    Mostafa Fayad 39
                                                Diagnosis of partially edentulous patients


vitamins should be advised a proper balanced diet. Patients with vitamin B2
deficiency will show angular cheilitis. Prophylactic vitamin A therapy is given
for xerostomic patients. Nutritional counseling is also done for patients show-
ing age-related changes such as osteoporosis.




       PROSTHODONTIC CARE

       The type of prosthesis, denture base material, anatomic palate, tooth
material and teeth shade should be decided as a part of treatment planning.
Depending upon the diagnosis made, the patient can be treated with an
appropriate prosthesis. For example:

 For a patient with few teeth, which are likely to be extracted an immediate
   or conventional, definitive or interim, implant or soft tissue supported
   dentures can be given.

 For patients with acquired or congenital deformities, a denture with an
   obturator can be given.



       In addition to the initial diagnosis the success or failure of denture
depend on also the treatment planning. In partially edentulous patient, there are
5 alternatives

1-fixed bridge.                            4-any combination.

2-removable partial denture                5-leave condition as it.

3-complete denture .                       6.Overdenture

1-fixed bridge

Indication:

A-GENERAL INDICATIONS:


                                                                   Mostafa Fayad 40
                                                  Diagnosis of partially edentulous patients


       1-for eliminating psychological trauma.

       2-in pt suffering from sudden bout of unconsciousness as in epilepsy.

       3-for orthodontic needs.

       4-as apart of overall periodontal and occlusal therapy.

       5-for better correction of speech.

       6-for better function and stability.

B-LOCAL INDICATIONS:.

       1-healthy abutments with suitable c/r ratio.

       2- if the abutment requires restoration.

       3- short span.

       4-lack of space for a suitable replacement.

       5-if the morphology of the abutment need changing.

       6-unfavourable angulations of the teeth for R P D ( Telescopic bridge)

Contraindication:

A-GENERAL CONTRAINDICATIONS:

1-inability of the patient to cooperate.

2-young or very old patient.

   In young, poor prognosis because of:

       • Short clinical crown                         • some teeth are not in
                                                      occlusion
       • Large pulp
                                                      • incomplete growth of the
       • High caries rate
                                                      bone of the jaw
       • Increase liability to trauma

                                                                     Mostafa Fayad 41
                                                   Diagnosis of partially edentulous patients


     in very old patient :

        • lack of P.D.L resiliency                     • the expectation of life short

        • increase abrasion                            • excessive bone resorpation

        • poor cooperation

 3- contraindication to L.A

 4- high caries rate

 5-gingival and periodontal disease

 6- bad oral hygiene

 7- un favorable reaction to the M.M

B- LOCAL CONTRA INDICATION

 1- long span

 2- when the bridge will occlude with opposing teeth on its end or 1/2 or less of
 its length

 3- unfavorable supporting structures of the abutment

 4- any apical infection

 5- insufficient effective root surface area

 6- weak crowns or small formed abutment

 7- deep sub gingivally carious abutment

 8- extensive bone resorpation of edentulous ridge

 9- unfavorable tilting or rotation of abutment

 10- increase possibility of further tooth loss in the same arch

 11- if the form of the bridge is an arc of a circle

                                                                      Mostafa Fayad 42
                                                Diagnosis of partially edentulous patients


12- abnormal occlusion, abnormal forces




2-Complete denture

Indication:

1-poor abutment

2- poor oral hygiene and rampant decay

3- cosmetically unacceptable ant. Teeth

4- rejection of professional advice

5- refusal mouth preparation

6- poor alignment

7- radiation therapy

3- Removable partial denture

Indicaton

1-long span with well supported abutment

2- free end saddles

3- multiple missing ant. teeth

4- weak abutment

5- presence of deep subgingival caries on abutment

6- increased caries index

7- need of cross arch stabilization (bracing) of remaining teeth

8- immediate replacement



                                                                   Mostafa Fayad 43
                                                  Diagnosis of partially edentulous patients


9- excessive bone loss

10- need for complete denture in future( due to increase possibility of further
tooth loss)

11- physical or emotional problems of pt.

12- patient desire (economic and time and preserve of sound teeth )

13- youth (< 17 y.) and old age

14- restore facial contour

15- alteration vertical dimension

16- transitional prosthesis

17- obdurate palatal cleft

18- extreme atrophic ridge

19- patient with previous unsatisfactory prosthetic

20- diabetic pt

Containdications:

A-Intraoral contraindication

        1-poor oral hygiene

        2- advanced P.L disease

        3- increase caries rate

        4- if morphology of abutment need changing (fixed)

        5- unfavorable angulations of the teeth

        6- short span (fixed)

B-Patient contraindication

                                                                     Mostafa Fayad 44
                                                  Diagnosis of partially edentulous patients


          1- un cooperative pt.

          2- with sudden pouts & unconsciousness or fits

          3- low and bad attitude

          4- poor general health

          5- patient unable to pay money

EXTRAORAL             FACTORS         THAT        INFLUENCE            TYPE         OF
PROSTHODONTIC SURFACE:

1-AGE:

     a- young patient under 25 y.

     • Not be rendered completely edentulous.

     • Avoid extraction

     • Age of man chronologic

     Physiologic

     psychologic

     b- old patient :

     need special care.

2-GENERAL HEALTH:

          • Poor health : trauma

          • Interim partial denture : prostheses of choice

          • Temporary partial denture instead of fixed partial denture

          • Rebase and relief & tissue materials need

3- SEX:

                                                                     Mostafa Fayad 45
                                               Diagnosis of partially edentulous patients


       Female:

       • Higher vanity index

       • Avoid loss of teeth and age changes

       • Need more esthetics ( P A P D avoid R P D )

       • First look is very important

4- ECONOMIC CONSIDERATION

R P D may need root canal treatment and crown inlays thus more cost.

5- SOCIOECONOMIC BACKGROUND

6- DESIRES AND ATTITUDE OF PATIENT

7- OCCUPATIONAL FACTORS

8- TIME FACTORS

Removable partial denture . may be used for long term prognosis, the best
R.P.D, service for many years.

Or for short term prognosis and in future the patient need complete denture,
must be simple in design and permit the addition of future teeth (additive
partial denture)

This temporizing treatment gives the patient experience in denture wearing and
in adaptation to artificial dentition.

The additive partial denture is particularly indicated in lower jaw. It is a
devisable to retain standing lower teeth, especially single standing canines to
delay recourse to the full lower denture and preserve the alveolar ridge
( support ). Overdenture: partial or complete overdenture




                                                                  Mostafa Fayad 46
                                                  Diagnosis of partially edentulous patients


Clinical factors related to metal alloys used for removable partial denture
frameworks: see denture base

       Various alloys can be considered for use, Practically all cast frameworks
for removable partial dentures are made from a chromium-cobalt alloy.

       The choice of the alloy from which the framework of a removable
partial denture will be constructed is logically made during the treatment-
planning phase.

       Mouth preparation procedures, especially the recontouring of abutment
teeth for the optimum placement of retentive elements, depend to a large extent
on the modulus of elasticity (stiffness) of a particular alloy.




Questions

1. Disscuss factors affecting selection the type of prostheses

2. Mention types of removable prostheses




                                                                     Mostafa Fayad 47
            BIOMICHANICS OF REMOVABLE PARTIAL DENTURE
Definition: The relationship between the biologic behavior of oral structures and
the physical influence of an R P D.

    Bio ------ pertaining to living systems-----inflammation, Caries, b.
    resorption….etc

    Mechanical ----- related to forces and its application to object-----
    looseness of teeth , bon resorption……etc

Mechanics may be classified into two general categories: Simple & complex.

        Complex machines are combination of many simple machines.

There are six simple machines

1 - lever                                   4-screw

2 - inclined plane                         5 –wheel

3 – wedge                                  6 – axle & pulley

A removable partial denture in the mouth can perform the action of two simple
machines, LEVER & INCLINED PLANE,
LEVER : The lever is a rigid bar supported at some point along it is length.

 There are three types of lever:

        Classification is based on location of fulcrum (support), resistance, and
direction of effort (force).

 The first type: the fulcrum (F) is in center of the bar, resistance (R) is at one and the
force (E) is at opposite end (called cantilever).

A cantilever: It is a beam supported only at one end, when force is directed against
unsupported end of beam cantilever can act as first class lever.

   The second-class lever: the fulcrum at one end, the force at opposite end & the
resistance in center. This type is seen as indirect retention in R P D.

  The third class lever: the fulcrum t one end & the resistance at opposite end & the
force in the center. This type is not encountered in R P D. (e.g. tweezers)

              Mechanical advantage      = Effort arm    /   Resistance arm

        The length of fulcrum to resistance is called Resistance arm, while the length of
lever from fulcrum to the point of application of force is called Effort arm.

       CLINICAL APPLICATION OF LEVER:

Every effort should be done to avoid class I lever (cantilever).      To avoid this
cantilever (lever class I) we can made either lever class II or using stress release
direct retainer.

        a) Lever class II

       Where the fulcrum at one end, the force at opposite
end & the resistance in center. This type called equipoise
force system.{see direct retainer}

       In this class, the occlusal rest (F) located mesially,
while the retentive tip (R) positioned distally, and the saddle
(E) located distal to the retentive tip i.e. the (R) located in
between the (F) & (E).

       b) Stress release direct retainer

          In general, if stress release is desirable,   a mesial rest with a mesial
undercut or distal rest with distal undercut should be used. A clasp with distal rest
and a wrought wire clasp arm engaging the mesial undercut is the exception.
       This can explain the difference between location of rest and retentive tip
mesially in gingivally approaching clasp as (McCr), and distally location as (Stew).
The both authors depending on the concept of stress release.
Inclined plane
       Inclined plane is nothing but two inclined surfaces in close alignment to
one another. The direct retainers and the minor connectors slide along the guide
plane of the teeth and can act as inclined planes if no prepared correctly.
       When a force is applied against an inclined plane it may produce two
actions:
            Deflection of the object, which is applying the force (Denture).
            Movement of the inclined plane itself (tooth) .These results should
              be prevented to avoid damage to the abutment teeth.


BIOMECHANICAL CLASSIFICATION OF R.P.D. ( Based on the
nature of the supporting tissues)
A. TOOTH BORNE (tooth supported or dentoalveolar supported).
   1. Abutment teeth border all edentulous areas where tooth replacement
      is planned.
   2. Functional forces are transmitted through abutment teeth to bone.
B. TOOTH - MUCOSA BORNE (tooth and mucosa supported, den to-
   alveolar and muco-osseous supported or extension base ).
   1. Exhibits one or more edentulous areas which are not bordered by
      abutment teeth (extension base RPDs).
   2. forces are transmitted through abutment and mucosa to bone.
   3. The majority of these are distal extension RPDs.
   4. This category may apply to tooth bordered situations when excessive
      abutment tooth mobility is present or when long span tooth bordered
      edentulous areas are present precluding primarily tooth support.
C. MUCOSA BORNE. (muco-osseous supported)
   1. Regardless of the natural teeth present, support is derived entirely
      from the mucoosseous segment.
   2. This category includes prostheses fabricated from hard or
      combinations of resilient and hard denture base materials such as
      stayplates which function as interim or transitional prostheses.
   3. These prostheses usually do not contain a metal framework and
      usually should not be considered definitive treatment.
CHARACTERISTICS OF FAVORABLE DENTO-ALVEOLAR
SUPPORT
A. TEETH.
   1. Structurally sound.
   2. Anatomically favorable.
      a. Root surface area.                     d. Presence of divergent
      b. Root morphology.                          roots.
      c. Presence of multiple                   e. Crown to root ratio.
         roots.                                 f. Axial inclination.
B.PERIODONTIUM.
   1. Normal (absence of periodontal disease).
      a. Gingival indices within normal limits.
       b. Absence of increasing mobility or hyper mobility.
   2. Anatomically favorable.
        a. orrnal epithelial and connective tissue attachment.
        b.Adequate zone of attached gingiva.
C. ALVEOLAR BONE.
   1. Favorable bone index.
   2. Anatomically normal.
      a. Bone height.                               mineralization.
      b. Degree of                               c. Presence of lamina dura.

CHARACTERISTICS OF FAVORABLE MUCO-OSSEOUS
SUPPORT
A. MUCOSA.
   1. Normal.
   2. Keratinized.
   3. Firmly bound.
B. SUBMUCOSA.
   1. Normal sub mucosa serves as an "hydraulic cushion".
   2. Firmly bound and dense.
C. BONE.
   1. Cortical bone.
   2. Favorable bone index.
   3. Presence of muscle attachments which direct tension to bone (or the
      equivalent in terms of resistance to pressure induced resorption).
OPTIMAL         FORCE        BEARING       MUCOOSSEOUS             ANATOMIC
REGIONS

A. MAXILLARY.
   1. Horizontal hard palate.
      a. Keratinized mucosa.
      b. Presence of fatty (anterior) and glandular (posterior) submucosa
         (excluding midline suture).
      c. Cortical bone.
  2. Posterior ridge crest.
     a. Keratinized mucosa.
     a. Presence of dense firmly bound submucosal connective tissue
        which may contribute to clinically observed resistance to pressure
        induced resorption.


Maxillary primary (10) supporting areas are the horizontal hard palate

and posterior ridge crest.

The periphery of the denture bearing area is non-contributory (N/C).

The midline suture often requires relief (R)

and the anterior ridge crest serves as a secondary (2°) supporting area.

B. MANDIBULAR.
   1. Buccal shelf. A primary force bearing area which is comprised of
      cortical bone. It extends from the base of residual ridge in the poste-
      rior part of the mandible to the external oblique ridge.
      a. Presence of submucosa.
      b. Cortical bone.
      a. Buccinator muscle attachment. The longitudinally directed fibers
         apply tension to the underlying bone but do not dislodge the
         denture base during contraction.
   2. Pear-shaped pad. The most distal extension of keratinized tissue
      covering the ridge crest. It is formed by the scarring pattern
      following the extraction of the most distal mandibular molar. It
      should be differentiated from the m~e posterior retromolar pad
      during clinical examination.
      a. Keratinized mucosa.
      a. Presence of dense firmly bound submucosa.
      a. Medial tendon of the temporalis muscle inserts lingually in the
         area of the apices of the mandibular third molars and applies
         tension to the underlying bone.
Mandibular primary (10) supporting areas are
the buccal shelf and pear-shaped pad.
The anterior facial incline of the ridge is non-contributory (N/C).
The lingual ridge inclines may require relief (R)
 and the genial tubercle area
and ridge crest serve as secondary (2") supporting areas.
      Stresses acting on a partial denture are transmitted to the teeth, and
tissues of the residual ridges. The stresses, which tend to move the denture in
different directions, may be summarized as follows:
     1- Masticatory stresses.
     2- Gravity tends to displace a maxillary denture downwards.
     3- Sticky food tends to pull the denture occlusally away from the tissues.
     4- Muscle pull and tongue action tend to displace a denture from its
        position.
  5- Intercuspation of teeth may tend to produce horizontal and rotational
     stresses unless the occlusion is balanced.


       FORCES ACTING ON REMOVABLE PARTIAL DENTURES

       The Supporting structures for removable partial are structurally adapted
to receive and absorb forces within their physiological tolerance. The ability of
these structures to tolerate forces is largely dependent upon the magnitude, the
duration and the direction of these forces in addition to the frequency of force
application.

      The magnitude of forces acting on partial dentures depends on age and
sex of the patient, the power of the muscles of mastication and the type of
opposing occlusion.

       Natural teeth are better able to tolerate vertical directing forces acting
on them. This is because more periodontal fibers are activated to resist the
application of vertical forces. On the other hand, lateral forces are potentially
destructive to both teeth and bone. Lateral forces should be minimized in order
to be within the physiologic tolerance of the supporting structures.
TYPE OF FORCES ACTING ON RPD
I- Vertical forces
A) Tissue-ward movements        B) Tissue-away movements
II- Horizontal forces:
A) Lateral movements            B) Antero-posterior movements.
III- Rotational forces:
      They are due to the variation in compressibility of supporting structures,
absence of distal abutment at one end or more ends of denture bases, and /or
absence of occlusal rests or clasps at any end of the bases.
1-Rotation of the anterior and posterior extension denture base around
coronal (transverse) fulcrum axis:
A) Rotation of the denture base towards the ridge around the fulcrum axis
joining the two main occlusal rests:
B) Rotation of the denture base away from the ridge around the fulcrum axis
joining the retentive tips of the clasps.
2-Rotation of all bases around a longitudinal axis parallel to the crest of the
residual ridge (Buccolingual or labiolingual).
3-Rotation about an imaginary perpendicular axis, this axis either near the
center of the dental arch in class I, or is the long axis of abutment tooth in class
II partial denture.

I- Tissue-ward movements
       a) Tissue-ward forces are, “Vertical forces acting in gingival direction
tending to move the denture towards the tissues”.

       They occur during mastication, swallowing and aimless tooth contact.
Biting forces falling on artificial teeth are transmitted to the soft tissues and
bone underlying the denture base.

        b) The partial denture should be designed to resist this movement by
providing adequate supporting components. This function of the partial denture
is called “Support”.

       Support is the function of partial denture which prevents movement of
the denture towards the tissues.

Support is mainly provided by:
 a) Properly designed supporting rests placed in rest seats, which are
   prepared on the abutment teeth,

 b) Broad accurately fitting denture bases in distal extension partial
   dentures. Therefore, the entire available ridge posterior to the abutment
   teeth must be covered with the denture.

 c) Rigid major connectors that are neither relieved from the tissues nor
   placed on inclined planes also provide support.

 d) Rigid portion of clasps placed over the survey line



II- Tissue-away movements
       a) Tissue-away dislodging forces are, "Vertical forces acting in an
occlusal direction tending to displace and lift the denture from its position”.

       Tissue-away forces occur due to: The action of muscles acting along
the periphery of the denture, gravity acting on upper dentures or by sticky food
adhering to the artificial teeth or to the denture base.

       b) The partial denture should be designed to resist this movement by
providing adequate Retention.

       Retention is “The function of partial denture which prevents the
denture from being displaced in an occlusal direction (away from the tissues)".



Retention in partial dentures is mainly provided by: {see direct retainer for
detail}

a- physical forces which arise from coverage of the mucosa by the denture.

b- Physiologic factors: Patient’s muscular control acting through the polished
surface of the denture.

c- Mechanical means such as clasps which engage undercuts on the tooth
surface.

In order to retain the denture, the anticipated intensity of occlusally
displacing force exerted during function should be less than the force
required for retaining the denture.
3) Horizontal movements:
A) Lateral movements

      a) Lateral forces are “Horizontal forces developed when the mandible
moves from side to side during function while the teeth are in contact”.

        Lateral movements have a destructive effect on teeth leading to tilting,
breakdown of the periodontal ligament and looseness of abutment teeth. The
application of lateral forces causes areas of compression of the periodontal
membrane, which leads to bone resorption. Hence lateral forces play a major
role in bone resorption,

        b) Partial dentures should be designed to prevent the deleterious effects
of lateral forces by using stabilizing or bracing components.

     Bracing is "The function of partial denture which resists lateral
movement of the appliance".

   Stabilizing components are "Rigid components of the partial denture that
assist in resisting horizontal movement of the denture". They help in
distributing lateral stresses to all supporting teeth:

 1.   Bracing clasp arms placed at or above the survey line of the tooth.

 2. Minor connectors in contact with axial (vertical) surfaces of abutment
   teeth

 3.   Proximal plates.

 4. Adequate extension of the flanges of the denture helps to stabilize the
   prosthesis against horizontal forces.

 5.   Rigid portions of clasps.
 6.   Lingual plates.
 7.   Rests - When the walls of the rest seat are relatively parallel to the path
   of placement (e.g. channel rests).


The magnitude of lateral forces could also be minimized by:

               1. Reducing cusp angles of artificial teeth.
               2. Providing balanced occlusal contacts free of lateral
                  interference.

   The removable partial denture being anchored to both sides of one arch and
joined by a rigid major connector can provide cross arch stabilization to forces
acting in bucco-lingual direction.



B) Antero-posterior movements

       a) Antero-posterior forces are "Horizontal forces which occur during
forward and-backward movement of the mandible while the teeth are in
contact". This may result in movement of the denture.

       There is natural tendency for the upper denture to move forward and for
the lower to move backward.

       b) Partial dentures should be designed to prevent the deleterious effects
of antero-posterior forces by

       Forward movement of the upper denture could be resisted by:

 1.   Anterior natural teeth.

 2.   Palatal slope.

 3.   Maxillary tuberosity.

 4.   The natural teeth bounding the edentulous space.

      The backward movement of the lower denture could be resisted by:

 1.   The slope of the retromolar pad.

 2.   The natural teeth bounding the saddle area.

 3.   Proximal plates.

VI- Rotational movements:
       a)Rotational forces are “Forces acting on the partial denture either in
vertical or horizontal direction causing rotation (torque) of the denture base
around an axis.

       In tooth supported removable partial dentures, the abutment teeth on
both sides of the edentulous area provide adequate support and resistance to
rotational forces through supporting rests and clasps placed on them.
       In distal extension partial denture when vertical forces are applied the
difference in displaceability of the supporting structures often results in rotation
of the partial denture around a fulcrum axis and application of torque on
abutment teeth.

       Rotational movements must be counteracted in the partial denture
design to minimize their destructive effect on both, teeth and the residual ridge.

       Rotational forces acting on distal extension partial denture may result
in three possible rotational movements these are

I- Rotation of the denture base around the fulcrum axis (Torque).

II- Rotation about a longitudinal axis formed by the crest of the residual ridge
(Tipping movement).

III- Rotation about an imaginary perpendicular axis near the center of the
dental arch (Fish tail movement).

I-Rotation of the denture base around fulcrum axis joining the principal
abutments:

       Movement of the component parts of the denture lying on the opposite
side of the fulcrum axis occur in a direction opposite to that of the applied
force. This leads to rotation of the denture:

       The fulcrum axis is an “imaginary line passing through teeth and
component parts of the partial denture around which the distal extension partial
denture rotates when a vertical force is applied”.

More than one fulcrum lines may identified for the same removable partial
denture depending on the direction and location for force application.

(a) Rotation of the denture base towards the ridge:

       This movement results from occlusal stresses occurring during
mastication and occlusion of teeth. The free extension denture base moves
tissue-ward while other components on the opposite side of the fulcrum line
moves away from the tissues. This result in rotation of the denture about a
diagonal supportive fulcrum line joining two occlusal rests on the most
posterior abutments on either side of the dental arch

   Tissue ward movement of the base could be limited by supporting
structures, which are:

 1.   Supportive form of the residual ridge,
 2.   Accurate and properly extended bases.

 3.   Artificial teeth set on the anterior two third of the base

   Flexible clasps are preferred over rigid clasping to reduce stresses and
torque applied on abutments. If the clasps are rigid, the abutments tend to rotate
distally during tissue ward movement of the denture base resulting in
periodontal breakdown and looseness of teeth.

(B) Rotation of the denture base away from the ridge.

       This movement occurs due to the pulling effect of forces applied by
sticky food, gravity on upper dentures and the elastic rebound of soft tissues
covering the edentulous areas.

Tissue-away rotation of denture base is counteracted by:

  1- Indirect Retainers: which are the components of partial denture located
     on the side of the fulcrum axis opposite to the distal extension base.

  2- The retentive tip of the clasp arm.

  3- Adequate coverage and extension of the base (direct indirect retention )

  4- Effect of gravity on mandibular bases.

II-Rotation around a longitudinal axis formed by the crest of the residual
ridge (Tipping movement)

       This rotation occurs due to application of vertical forces on one side of
the arch only. It causes twisting of the denture base.

This movement is counteracted by:

  1- Cross arch stabilization (The action of clasps on the opposite side of the
     arch).

  2- Broad base coverage.

  3- Proper placement of artificial teeth (teeth on the ridge or lingualized
     occlusion).

  4- Narrow teeth bucco-lingually.

  5- The effect of rigid major connectors.

III- Rotation around an imaginary perpendicular axis near the center of
the dental arch
                  Application of horizontal or off-vertical force results in rotation around
           an imaginary vertical axis located either about the axis of abutment in class II
           or near the center of the dental arch, lingual to anterior teeth in class I.

                  It results due to the application of masticatory forces falling on distal
           extension bases causing buccolingual movement of the base. This rotation is
           called fishtail movement.

           This movement is counteracted by :

              1- Providing adequate bracing components in the partial denture.

              2- A rigid major connector.

              3- Broad base coverage.

              4- Balanced contact between upper and lower teeth.

                  Forces accruing through a removable restoration can be widely
           distributed, directed, and minimized by the selection, the design, and the
           location of components of removable partial dentures and by developing a
           harmonious occlusion.



           Force                  Cause of the Force          Counteraction of the force           Function
I- Vertical Forces :            Functional        movements - Rests placed on abutments in - Support
1- Tissue-ward displacing during               mastication, bounded saddles.
forces.                         swallowing              and - Rests & proper base coverage in
                                occlusion of upper and free end bases.
                                lower teeth.                 - Maxillary connectors
2-   Occlusally      displacing Pulling effect of sticky - Retainers.                             - Retention
forces.                         food Gravity on upper - Adhesion & cohesion between
                                dentures. Muscles acting denture base & tissues
                                on periphery of denture
II- Horizontal Forces           Side to side movement of - Rigid bracing clasp arms.              - Bracing
1- Lateral forces.              the mandible while teeth - Major connectors.                      (Stabilization
                                are in contact.              - Balanced occlusion.
                                                             - Maximum extension of the flanges
2- Antero-posterior forces     Forward and backward - Abutments adjacent to the denture.       -
                               movement of mandible              - Guiding planes.             Stabilization
                               while teeth are in contact


III- Rotational forces :       - Functional movements - Supporting rests.                   - Support
1- Vertical forces in gingival while       teeth       are   in - Properly adapted bases.
direction in free-end saddles. occlusion.                        .




2- Vertical forces in occlusal - Sticky food, gravity on - Indirect retainers.              -Indirect
direction in free-end saddles. upper       dentures,     elastic - Direct retainers.        retention.
                               rebound of tissues under
                               the base.




           Factors affecting stress generation and transfer
               1- Length of span: - the longer edentulous span, the greater force will be
                  transmitted to the abutment. so the Posterior teeth should be preserved
                  as far as possible to reduce the length of the edentulous span

               2- Quality of the supporting tissues:

                        Form of the residual ridges: large well developed ridges, absorb
                         more amount of force than small, thin ridge.

                        Type of mucosal covering : atrophic and flabby mucosa are not
                         preferred.

               3- Quality of clasp: - the more flexible clasp arm, the less force transmitted
                    to the abutment.
               4- Clasp design: - a passive clasp when it is completely seated on the
                    abutment teeth will exert less stress on the tooth than the non passive.
                         A clasp should be designed so that the reciprocal arm contacts the
                    tooth before the retentive tip passes over the greatest bulge of the tooth
                    during insertion and it should be the last component to lose tooth
                    contact during removal of the prosthesis.
5- Length of the clasp.
          Doubling the length increases the flexibility by five times. This
    decreases the stress on the abutment tooth. Using a curved rather than a
    straight clasp on an abutment tooth will aid to increase the clasp length
 6- Material used in clasp construction
            A clasp constructed of chrome alloy will exert more stress on
     the abutment tooth than a gold clasp because of its greater rigidity. To
     decrease the stress, the chrome alloy clasps are constructed with a
     smaller diameter.
7- Abutment tooth surface: - the surface of a gold crown or restoration
    offers more functional resistance to clasp arm movement than does of
    enamel surface of a tooth therefore greater stress is exerted on the
    abutment.

8- Occlusal relationship of the remaining teeth and orientation of the
   occlusal plane.
     Type of the opposing occlusion
     Harmony of the occlusion should be present.
     Improper occlusal relationship and a steep occlusal plane tend to
       increase the amount of force acting on the denture. The force
       applied on natural teeth is 300 pounds and the force acting on
       artificial teeth is about 30 pounds. Poor occlusal relationship can
       lead to supra-eruption of the opposing natural teeth.
9- Musculature of the patient.

10- Response of oral structures to previous stress. The periodontal
   condition of the remaining teeth, need for splinting and the amount of
   abutment support remaining are all a result of the previous stress
   subjected on the oral tissues.
      RESPONSE OF FORCE BEARING TISSUES TO
             MECHANICAL LOADING
      The forces directed to the supporting tissues will be partially absorbed
and partially transmitted to adjacent tissues.

      The percentage of force absorbed or transmitted will vary depending
upon which tissue is involved.

       Bone is the tissue which ultimately absorbs the greatest amount of the
force applied to both the muco-osseous and dento-alveolar segments.

A.DENTO-ALVEOLAR SEGMENT.

1.Tooth.

a. Structurally sound vital teeth are capable of withstanding normal functional
forces.

b. Excessive forces may result in adverse effects.

    Structural failure (tooth fracture).

    Tooth movement.

    Pulpal irritation. Reversible pulpitis (hyperemia) or irreversible pulpitis,

c. Structurally compromised teeth may fail in response to normal functional
forces.

    Teeth with large intracoronal restorations.

    Endodontically treated teeth.

2.Periodontium

      including gingiva, crevicular epithelium, junctional epithelium,
connective tissue attachment, cementum, periodontal ligament and alveolar
bone.

a. A normal periodontium permits some force absorption without damaging
effects.

b. Excessive forces may increase the width of the periodontal ligament and
result in increased tooth mobility.
c. Plaque induced inflammation may compromise the periodontium. It can lead
to apical migration of the crevicular epithelial attachment (functional
epithelium) and destruction of the fibroblasts and connective tissue of the
connective tissue attachment. In the presence of inflammation normal
functional forces may accelerate the rate of periodontal attachment loss.

3.Alveolar bone.

a. Pressure - tension theory. Bone tends to resorb in response to compressive
force and to be stimulated by tensional force. In order to preserve remaining
alveolar bone, it is important that functional forces be transmitted to bone
primarily as tension rather than pressure whenever possible.

       In tooth borne situations the majority of functional forces are transmitted
as tension to bone through proper rest design and rest seat preparation. In tooth-
mucosa borne situations some of the vertical seating forces are transmitted as
tension to the bone through the rests. Horizontal forces are transmitted as a
combination of compressive and tensional forces to the alveolar bone (e.g.
those forces directed through bracing clasps, proximal plates and minor
connectors contacting proximal tooth surfaces and guiding planes). Vertical
displacing forces are transmitted to the bone as both compressive and tensional
forces (e.g. sticky foods or retentive clasps engaging undercuts).



b.Bone index or Bone factor. The response of bone to pressure varies in terms
of the rate of resorption depending on genetic, nutritional, hormonal and
biochemical and other intrinsic factors. The bone index is determined by
analyzing the previous response of bone to force.

c. Cortical vs. cancellous bone. Cortical bone is more dense, more highly
mineralized, less cellular, and less metabolically active. It tends to be more
resistant to pressure induced resorption than cancellous bone. Lamina dura is
cortical bone.

d. Excessive forces which increase compressive components of forces
transmitted to bone may increase the rate of bone resorption.

e. Periodontal disease. The presence of plaque induced periodontal disease is
associated with a loss of bone height. Moderate forces may accelerate the
disease process resulting in further bone loss, less bone support, and increased
mobility of the teeth.
B. MUCO-OSSEOUS SEGMENT.

1.Mucosa.

a.Normal. firmly bound, keratinized tissues withstand mechanical forces within
physiologic limits.

b. Excessive mechanical forces may cause mucosal ulceration (e.g. denture
sore spots).

2.Submucosa

a. Provides an "hydraulic cushion" effect.

b. Increased thickness of the submucosa improves tolerance of the residual
ridge to applied forces.

3.Bone

a. Pressure-tension theory. The functional loading of a tooth-mucosa borne
denture base transmits force to the bone of the rnuco-oss ous segment almost
exclusively as pressure which tends to cause resorptive changes. Resorption
occurs in proportion to the intensity, duration, and direction of the applied force
and as influenced by the bone factor. With some longer span tooth borne partial
dentures or when excessive mobility of abutment teeth is present some force
may also be delivered through the mucosa to the underlying bone as pressure.

b. Bone index. The bone index of the alveolar bone surrounding natural teeth
may differ from that of the bone comprising the residual ridges. (Fig. 3-6)

c. Cortical vs. cancellous bone. The residual ridge crest is comprised mainly of
cancellous bone and is less resistant to resorption. The facial and lingual
inclines of the residual ridges are comprised of cortical bone and are more
resistant to remodelling. The rate of cancellous bone resorption has been
described as being approximately three times that of cortical bone.

d.Excessive forces may increase the rate of bone resorption.

e. Moderate forces may result in accelerated bone resorption when intrinsic
factors, local abnormalities or systemic disorders compromise the bone index
of the individual.
REACTION OF TISSUE TO METALLIC COVERAGE

       The reaction of tissue to coverage by the metallic components of a
removable partial denture has been the subject of significant controversy,
particularly in regions of marginal gingiva and broad areas of tissue contact.

These tissue reactions can result from

1) Pressure from lack of support,

2) lack of adequate hygiene measures,

3) prolonged contact through continual use of a prosthesis.

        Pressure occurs at regions where relief over gingival crossings and
other areas of contact with tissue that are incapable of supporting the prosthesis
is inadequate. Impingement will likewise occur if the denture settles because of
loss of tooth and/or tissue support. This may be caused by failure of the rest
areas as a result of improper design, caries involvement, fracture of the rest
itself, or intrusion of abutment teeth under occlusal loading. It is important to
maintain adequate relief and support from both teeth and tissue. Settling of the
denture because of loss of tissue support may also produce pressure elsewhere
in the arch, such as beneath major connectors. Settling of a prosthesis must be
prevented or corrected if it has occurred. Excessive pressure must be avoided
whenever oral tissue must be covered or crossed by elements of the partial
denture.

       Lack of adequate hygiene measures can result in tissue reactions
because of an accumulation of food debris and bacteria. Coverage of oral tissue
with partial dentures that are not kept clean irritates those tissue because of an
accumulation of irritating factors. This has led to a misinterpretation of the
effect of tissue coverage by prosthetic restorations. An additional hygiene
concern relates to the problem of maintaining cleanliness of the tissue surface
of the prosthesis.

        The first two causes of untoward tissue reaction can be accentuated the
longer a prosthesis is worn. It is apparent that mucous membranes cannot
tolerate this constant contact with a prosthesis without resulting in
inflammation and breakdown of the epithelial barrier. Some patients become so
accustomed to wearing a removable restoration that they neglect to remove it
often enough to give the tissue any respite from constant contact. This is
frequently true when anterior teeth are replaced by the partial denture and the
individual does not allow the prosthesis to be out of the mouth at any time
except in the privacy of the bathroom during tooth brushing. Living tissue
should not be covered all the time or changes in those tissue will occur. Partial
dentures should be removed for several hours each day so that the effects of
tissue contact can subside and the tissue can return to a normal state.

        Clinical experience with the use of linguoplates and complete metallic
palatal coverage has shown conclusively that when factors of pressure,
cleanliness, and time are controlled, tissue coverage is not in itself detrimental
to the health of oral tissue.



         Controlling Stress by Design Considerations
1- Direct Retention :

1.     Clasp
  The retentive clasp arm is the element of RPD that is responsible for
transmitting most of destructive forces to the abutment teeth. A RPD should
always be designed to keep clasp retention to a minimum yet provide
adequate retention to prevent dislodgment of the denture by unseating
forces. It should also be remembered that the retentive clasp should be
designed such that it is active only during insertion and removal.

2.     Forces of adhesion and cohesion
  To secure the maximum possible retention through the use of forces of
adhesion, the denture base should cover the maximum area of available
support and must be accurately adapted to the underlying mucosa.

3.     Frictional control
  The RPD should be designed so that guide planes are created on as many
teeth as possible. Guide planes are areas on teeth that are parallel to the path
of insertion and removal of the denture. The plane may be created on the
enamel surfaces of the teeth or restorations placed on teeth. The friction of
RPD against parallel surfaces can contribute significantly to retention of the
denture.

4.      Neuro-muscular control
  The design and contour of the denture base can greatly affect the ability of
lips, checks and tongue to retain the prosthesis. Any over-extension of the
denture base either facially, lingually in the mandible or posteriorly onto the
soft palate will contribute to the loss of retention and the abutment teeth
bearing the direct retainers will be over stressed.
5.    Clasp Position
 a- Quadrilateral configuration

  Four abutments are utilized for clasping.       Quadrilateral configuration is
indicated in Class III particularly when there   is a modification space on the
opposite side of the arch. A retentive clasp     should be positioned on each
abutment adjacent the edentulous space.          This result in denture being
confined within the outline of four clasps

  b- Tripod Configuration
  Tripod clasping is used primarily for class II arches. If there is a modification
space on the edentulous side the teeth anterior and posterior to the space are
clasped. If a modification space is not present. One clasp on the edentulous
side of the arch should be positioned as far posterior as possible and the
other, as far anterior as factors such as interocclusal space, retentive
undercut, and esthetic considerations will permit. By separating the two
abutments on the tooth-supported sides as far as possible, the largest possible
area of the denture will be enclosed in the triangles formed by the clasps.

 c- Bilateral configuration

  Most RPD with bilateral distal extension group in class I fall into bilateral
configuration. In the bilateral configuration the clasp exert little neutralizing
effect on the leverage induced stresses generated by the denture base. These
stresses must be controlled by other means.

6.      Clasp design :
  a- Circumferential clasp :
  The conventional circumferential cast clasp originating from a distal occlusal
rest on the terminal abutment tooth and engaging a mesio-buccal retentive
undercut should not be used on a distal extension RPD. The terminal of this
clasp reacts to movement of the denture base toward the tissue by placing a
distal tipping, or torquing, force on the abutment teeth. This particular force is
the most destructive force a retentive clasp can exert. This clasping concept
must be avoided.

  On the other hand if the circumferential clasp with mesial occlusal rest
approaches a disto-buccal undercut form the mesial surface of the abutment,
is acceptable. The effect on the abutment is reversed from that of the
conventional clasp. As the occlusal load is applied to the denture base, the
retentive terminal moves further gingivally into the undercut area and loses
contact with the abutment teeth. In this manner torque is not transmitted to
the abutment tooth.



 b- Vertical projection or Bar clasp :

  The vertical projection clasp, or bar clasp is used on the terminal abutment
tooth on a distal extension RPD when the retentive undercut is located on the
disto-buccal surface. As the denture base is loaded toward the tissue, the
retentive tip of the clasp rotates gingivally to release the stress being
transmitted to the abutment tooth.

  c- Combination clasp :

  When a mesio-buccal undercut exist on abutment tooth adjacent to a distal
extension edentulous ridge, the combination clasp can be employed to reduce
the stress transmitted to the abutment tooth. wrought alloy wire, by virtue of
its internal structure, is more flexible than a cast clasp. It can flex in any plane,
whereas a cast clasp flexes in the horizontal plane only. The wrought wire
retentive arm has a stress-breaking action that can absorb torsional stress in
both vertical and horizontal planes.

 Flexible clasps produce the least stress and rigid cast circumferential clasps
produce the maximum stress in an abutment.

2- Indirect Retention

       The indirect retention is essential in the design of class I and II RPD, by
using the mechanical advantages of leverage; it counteracts the forces
attempting to move the denture base away from the residual ridge by moving
the fulcrum farther from the force.

        In class I prosthesis, the fulcrum line would be moved from the tips of
the retentive clasp to the most anteriorly located component, the indirect
retainer. Because the indirect retainer resists lifting forces at the end of a long
lever arm, it must positioned in a definite rest seat so that the transmitted
forces are diverted apically through the long axis of abutment tooth. The
indirect retainer also contributes to a lesser degree, to the support and
stability of the denture.

Class I : indirect retainer must always used.
Class II: it is not as critical as in class I but still required. Modification space
can provide indirect retention. A definitive occlusal rest seat anterior may
increase the effectiveness of indirect retention.

Class III : indirect retention is not ordinarily required except in :

  - long lingual bar major connector to provide additional vertical support.
  - Lingual plate major connector.
Class IV : is considered reverse of class I and II. The lever arm is anterior to the
fulcrum line, so the indirect retainer must be located as far posterior as
possible. Occlusal rests and clasp assemblies are placed on the most posterior
teeth for both direct retention and support.



3- Occlusion

       The occlusal surfaces, or food table, of artificial teeth can transmit
various amounts of stress to the supporting structures. A large or broad
occlusal surface deliver more stress than does one that has been reduced in
bucco-lingual width. The number of teeth replaced may also be reduced to
decrease stress. Harmonious occlusion should be developed.



4- Denture Base

       The denture base should be designed to cover as extensive an area of
supporting tissue as possible. The stress created by the partial denture in
function will thus be distributed over a large area, so no single area will be
subjected to stress beyond its physiologic limit. The denture base flange
should be made as long as possible to help stabilize the denture against
horizontal movements.

       The distal extension denture base must always extend onto the
retromolar pad area in the mandible and cover the entire tuberosity of the
maxilla. Both structures are capable of absorbing more stress than alveolar
ridge anterior to them.

      The type of impression used to record the residual ridge will influence
the amount of stress the residual ridge can effectively absorb. Several
techniques are used to make functional impression of the residual ridge. Each
technique is based on the theory that if the ridge were recorded in its
functional state rather than its resting form, when the denture base is actually
subjected to occlusal loading, the tissue would not displaced to any great
stint. The magnitude of stress transmitted to the abutment teeth, therefore,
would be minimal.

      Denture base should be accurate and stable. The polished surface
should have the proper form and contour.

5- Major Connector

        In the mandibular arch the lingual plate major connector that is
properly supported by rests can aid in the distribution of functional stresses to
the remaining teeth. It is particularly effective in supporting periodontally
weakened anterior teeth. The lingual plate also adds rigidity to the major
connector. The added rigidity contributes to the effectiveness of cross-arch
stabilization.

       In the maxillary arch the use of a broad palatal major connector that
connects several of the remaining natural teeth through lingual plating can
distribute stress over a large area. The major connector must be rigid and
must receive vertical support through rests from several teeth.

       It should distribute the occlusal load over a wide area and at the same
time produce the least amount of stress. There are three important principles
for design exclusively used for a major connector. They are:

           L-bar or L-beam principle.

           Circularconfiguration.

           Strut configuration.

       L-bar or L-beam principle

      The L-beam or L-bar or Linear beam theory states that the flexibility of
a bar is directly proportional to the length of the bar and inversely
proportional to its thickness.

      When a load is placed on the bar or beam supported at its ends,
maximum stress is present in the centre and zero stress at the supported
ends.
       A bar supported at both its ends can be divided into two parts namely
the parabolic and quartic parts. The parabolic part forms the middle2/4th of
the distance between the supports and the remaining l/4th on either sides of
the bar form the quartic part.

       The parabolic part shows maximum stress concentration and the
quartic part shows minimum or zero stress concentration. Hence, if we design
a bar such that it has a smaller parabolic part and a larger quartic part it will
be less flexible. The material becomes more rigid (less flexible) without adding
bulk to the bar.

        The next question is how do we do this? The answer is very simple. IT
we bend the bar on either side, the length of the bar lying in the quartic part
will increase.

        Now apply this concept in the design of a major connector. The palate
has a flat vault and two lateral slopes.

      If the slopes are shallow, the quartic part of the major connector also
decreases leading to increased flexibility of the prosthesis under occlusal load.
The major connector should be located and designed such that it lies over the
steeper slopes in the palate.

       Hence, broad palatal major connectors, palatal strap major connectors
can be fabricated with lesser bulk of material (but with adequate rigidity)
because it extends in three planes (one central vault and two lateral slopes)
with the length of the quartic part (the two lateral slopes) being greater than
the parabolic part.

       Circular configuration

      The advantage of a circle is that it is a continuous unit without an end.
Any force acting on a circular bar can be easily distributed all along the
circumference. Hence, a circular bar is more rigid than a linear bar with the
same area of cross section. This concept can be used to reduce the bulk of the
major connector with a circular configuration anteroposterior double palatal
bar and closed horseshoe.
       Strut configuration

        According to this configuration,
a straight bar bent at its ends near the
support is more rigid because, the
bent slopes of the bar aid to transfer
the load acting on the horizontal
portion.

       This is similar to the linear bar
theory (L-beam discusses stress
concentration but struts discuss stress
distribution).

       The major connector on a
narrow vault is more rigid than a major
connector extending over a shallow
vault. In other words, the major
connector extending in two different
planes has more rigidity.

       This concept is seen in the
anterior plate of the double palatal
bar, where the slope of the rugae area acts as an additional strut.



6- Minor Connector

   The most intimate tooth-to-partial denture contact takes place between
the minor connector joining the clasp assembly to the major connector and
the guiding planes on the abutment tooth surfaces. This close metal-to-
enamel contact serves two purposes:

 1- It offers horizontal stability of RPD against lateral forces.
 2- Through the contact of the minor connector and the abutment teeth, the
    teeth receive stabilization against lateral stresses.
7- Rests

      One of the most critical points of the rest seat is that the floor of the
preparation must form an angle of less than 90 degrees with the long axis of
the tooth. This permits the rest, whether occlusal, incisal or lingual, to grasp
the tooth securely and prevent its migra on. If more than 90 degrees, an
inclined plane action is set up and stress against the abutment tooth is
magnified.

       In class I and II RPD the rest seat preparation must be saucer-shaped,
completely devoid of any sharp angles or ledges. As the forces are applied to
the partial denture, the rest must be free to move within the rest seat to
release stresses that would otherwise be transferred to the tooth. The more
teeth bear rest seats, the less will be the stress placed on each individual
tooth.



8- Splinting of abutment teeth :

  Adjacent teeth may be splinted by means of crowns to control stress
transmitted to a week abutment tooth. splinting two or more teeth actually
increases the periodontal ligament attachment area and distributes the
stress over a large area of support. It also stabilizes the abutment teeth in a
mesio-distal or antro-posterior direction.

  Splinting could be achieved by clasping more than one tooth on each side of
the arch using a number of rests for additional support and stabilization and
preparing guiding planes on as many teeth as possible to contribute to
horizontal stabilization of the teeth and the prosthesis. The multiple clasps
should not all be retentive.

 Splinting is indicated for the following clinical conditions.

      Abutments with a tapered or short root.

      Terminal abutments located on the edentulous side of a distal
        extension denture base.

      Fixed splinting is given if there is some loss of periodontal attachment,
         after a periodontal disease and therapy.
                                                                 PARTIAL DENTURE DESIGN

             ESSENTIALS OF PARTIAL DENTURE DESIGN
                               Decision Making in RPD Design


       Designing of partial denture necessitates a proper planning for the form and
extent of a dental prosthesis and studying of all the factors involved.
        The prosthesis must be designed following the most favorable biomechanical
  principles, as the proper design helps in reducing the harmful effects on the
  supporting structures.



A Properly constructed partial denture must achieve:
    A- Support: Adequate distribution of the load to the teeth and mucosa.
    B- Retention: Sufficient resistance to vertical displacing forces.
    C- Bracing: Anchorage sufficient to resist lateral and rotational forces.
    D- Stabilization: Sufficient resistance to resist tipping forces.
    C- Reciprocation: Nullifying the effect of pressure on one side of a tooth by the
      application of pressure, equal in amount but in an opposing direction, on the
      opposite side of the tooth.



 PHILOSOPHYOF PARTIAL DENTURE DESIGN
There are four design concepts, which can be used to distribute the force evenly along
the tissues and supporting tooth structure. They are :
    Conventional rigid design.
    Stress equalization.
    Physiologic basing.
    Broad stress distribution.


Conventional Rigid Design
The denture is designed with rigid component which act like a raft foundation to
evenly distribute the forces on the supporting tissues. This design is used in all general
cases. The flexible component of these dentures is their retentive terminal.
Advantages

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                                                                 PARTIAL DENTURE DESIGN

    Easy to construct and economical.
    Equal distribution of stress between the abutment and the residual ridge.
    Reduced need for relining as the ridge and abutment share the load.
    Indirect retainers prevent rotational movement and also stabilize the denture
       during horizontal movements.
    Less susceptible to distortion.
Disadvantages
    Increased torquing forces on the abutment teeth.
    Rigid continuous clasping may damage the abutment teeth.
    Dovetail intracoronal retainers cannot be used in these cases as tipping forces
       from the denture base will be directly transmitted to the abutment teeth.
    Tapered wrought wire retentive arm (combination clasp) cannot be used, as it is
       difficult to construct.
    Relining is difficult and inappropriate relining leads to damage of the abutment
       teeth.


Stress Equalization or Stress Breaker or Stress Directing Concept
       A stress breaker is defined as, “A device which relieves the abutment teeth of
all or part of the occlusal forces" - GPT.
       A stress director is a device that allows movement between the denture base
and the direct retainer which may be intracoronal or extracoronal. Dentures with a
stress breaker are also called a broken stress partial dentures or articulated prostheses.
       We know that the soft tissues are more compressible than the abutment teeth. In
a tooth tissue supported partial denture, when an occlusal load is applied, the denture
tends to rock due to the difference in the compressibility of the abutment teeth and the
soft tissue As the tissues are more compressible, the amount of stress acting on the
abutments is increased. This can produce harmful effects on the abutment teeth.
       In order to protect the abutment from such conditions, stress breakers are
incorporated into a denture.
       There are two types of stress breakers:
       Type I



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                                                                PARTIAL DENTURE DESIGN

       Here a movable joint is placed between the direct retainer and denture base.
This joint may either be a hinge or a ball and socket or a sleeve and cylinder. Adding
these stress breakers to the junction of the direct retainer and the denture base, allows
the denture base to move independently.
       This decreases the amount of force acting on the abutment. The combined
resiliency of the periodontal ligament and the stress director will be equal to the
resiliency of the oral mucosa overlying the ridge.
       Examples for hinges include DALBO, CRISMANI, ASC 52 attachments.
       Type I I
       It has a flexible connection between the direct retainer and the denture base. It
can be a wrought wire connector, divided or split major connector or a movable joint
between two major connectors.
       In a split major connector, the major connector is split by an incomplete cut
parallel to the occlusal surface of the teeth into two units namely the upper unit (more
near to the tooth) and the lower unit. The denture base is connected to the lower unit
and the rests and direct retainers are connected to the upper unit.
       Advantages
    The alveolar support of the abutment teeth is preserved as the stresses acting on
       the abutment teeth are reduced.
    The stress on the residual ridge and the abutment teeth are balanced.
    Weak abutment teeth are well splinted even during the movement of the denture
       base. Abutment teeth are not damaged even if relining is not done appropriately
       (after the denture wears out).
    Minimal requirement of direct retention.
    Movement of the denture base produces a massaging effect on the soft tissues..
       This avoids the frequent need for relining and rebasing.
Disadvantages
    Design is complicated and expensive.
    The assembly is very weak and tends to fracture easily. Distorts to rough
       handling.
    It is difficult to repair.


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                                                                 PARTIAL DENTURE DESIGN

    It can be used only to counter the vertical forces on the denture. Inability to
       counteract lateral stress acting on the ridge leads to ridge resorption.
    Reduced stability against horizontal forces.
    Both vertical and horizontalforces are concentrated on the ridge leading to
       resorption.
    Inappropriate relining leads to excessive ridge resorption.
    Reduced indirect retention.
    The split major connector tends to collect food debris at the area of split.


Physiologic Basing
       This technique distributes the occlusal load between the abutment teeth and the
soft tissues by fabricating a denture based on a functional record. Functional record is
obtained by recording the tissues under occlusal load or by relining the denture under
functional stress. This technique involves making an impression of the soft tissues in a
compressed state.
       The denture fabricated using a functional impression has one major
disadvantage. That is the denture tends to compress the soft tissues even at rest. This
can lead to excess ridge resorption. Since the denture is fabricated using a functional
record (compressed tissues), the soft tissues offer more resistance to further
compression. This increased resistance to compression provided by the oral mucosa
equates to that of the periodontal ligament of the abutment tooth. In this manner the
abutment tooth is protected from excessive forces and the denture can distribute
occlusal load evenly to the teeth and tissues.
Requirements for Physiological Basing
    rigid metal framework
    Functional occlusal rests
    Indirect retainers to provide additional stability.
    Well-adapted, broad coverage denture bases.
Advantages
    Good adaptation of the denture base.
    Simple design and economical.
    Minimal direct retention decreases the

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                                                                PARTIAL DENTURE DESIGN

    functional stress on the abutment tooth.
Disadvantages
    Decrease in the number of retentive components provides less stability.
    The denture tends to lift at rest. This leads to premature contacts.
    Indirect retention is decreased due to vertical movement of the denture due to
       tissue rebound at rest.


Broad Stress Distribution
       According to this philosophy of design, the occlusal load acting on the denture
should be distributed over a wider soft tissue area and maximum number of teeth. This
is achieved by increasing the number of direct retainers, indirect retainers, and rests
and by increasing the area of the denture base.
Advantages
    This design with multiple clasps acts as a form of removable splinting.
    It increases the health of the abutment teeth (due to splinting action).
    Easier to construct and economical.
Disadvantages
    Less comfortable.
    Difficult to maintain adequate oral hygiene.




                    Designing of Partial Denture

Sequence of designing partial dentures:
1- Denture base designing.
2- Designing for support.
3- Providing retention.
4- Designing for bracing and reciprocation.
5- Designing for resistance to anteroposterior movements of the saddles.
6- Connecting the saddles and retainers.
7- Esthetics



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                                                               PARTIAL DENTURE DESIGN




I- Denture base designing:
  It is the part of the partial denture which rests on the mucoperiosteum and to which
the denture teeth are attached.
Functions:
1-Retain the artificial teeth.
2-It provides addition retention to the prosthesis.
3-It provides addition stabilization for the RPD against the horizontal forces.
4-It provides support for the distal extension base RPD.
5-the contour of its polished surface provide a stabilizing and retentive effect when
acted on by the oral musculature.
Design:
       It is desirable to extend the denture saddles into the sulcus to assure the
maximum coverage especially in mucosa and tooth-mucosa supported RPD.
Types of contact between the denture and abutment teeth:
1- Closed design with long guiding plane.
2- Open design with short guiding plane.
3- Open design without guiding plane and with wide embrasure.


II-Designing for support:
Definition:
It is the resistance against the vertical seating forces which occurring during
{mastication, swallowing and Para function}.
Classification of RPD according to their support:
(1) tissue-borne dentures:
Gets all its support from the soft tissue covering the jaws.
(2) tooth-borne dentures:
Gets all its support from the natural teeth.



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                                                                          PARTIAL DENTURE DESIGN

         They are a very small dentures which replacing one or two teeth on one side only and
         often they are called (removable bridges).
         (3) Tooth-and tissue born dentures:
         They are supported by the soft tissue and the natural teeth.
         The best example of this type is the RPD with distal extension bases. The tooth
         structure provides the support interiorly, where soft tissue supports the denture base
         posteriorly.


         Support can provided from:
         1- Denture base.
         2- Maxillary major connectors.
         3- Rests.
         4- Rigid portions of the clasps placed above the survey line.
         Number of rests:
1-          Required number if possible 4 well distributed rest. Such a case will be considered
         as self-indirect retained case.
2-          If not possible, 3 will be required, 2 will make fulcrum line (the two main
         posteriors) and the 3rd one will act for support and indirect retention.
3-          In some cases the possible number will be only 2 , in such case , the indirect
         retention will be from the resistance form by maximum coverage & seal, as complete
         denture base.


         III-Designing for retention:
         It is the resistance to vertical dislodging force; which occurs during:
         1- Mastication of sticky food.
         2- Muscles of lips, tongue, and cheeks.
         3- Gravity on maxillary denture.
         Means of retention: {see direct retainer for detail}
              A] Physical factors
           Adhesion between saliva / denture & tissue
           Cohesion between saliva molecules
           surface tension

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                                                                     PARTIAL DENTURE DESIGN

      Atmospheric Pressure
      Effect of Gravity
      Plastic molding between tissues / denture polished surfaces aid to little extent in
    retention of partial denture
           b] Mechanical means
           (1) Direct retainers:
              A- Intracoronal (precision attachments).
              B- Extracoronal (clasps)
           (2) Frictional fit between the denture and the abutment teeth.
           (3) Parts of the denture base engaging in undercuts on the teeth.
           (4) Parts of the denture base engaging in undercuts on the soft tissues.
           (5) Indirect retainers. {Prevent rocking movements of the denture}.
           C] Physiological means of retention:
           1- The physiologic molding of the tissues around the polished surfaces of the
           denture helps to perfect the border seal.
           2- Neuromuscular control
    Direct retainers:
    A- precision attachments:
       •    They are fitted more to the small unilateral RPDs (side-plates).
       •     They are bought ready-made (usually the mail portion is attached to the
            denture, while the other is soldered into a crown or large inlay in an abutment
            tooth.)
    B- Clasps:
    1- To resist displacement of the denture by vertically applied forces .
    2- To resist displacement of the denture by horizontal applied forces.


    Selection of clasp:
               Selection of the clasp depends mainly on (type of support, presence of
      undercut area, and esthetics).
      1- For bounded saddles: the retentive undercut present is used with any acceptable
      clasp type.



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                                                                 PARTIAL DENTURE DESIGN

  2- for distal extension base: Retainers for distal extension partial dentures, although
  retaining the prosthesis, must also be able to flex or disengage when the denture
  base moves tissueward under functional. stress releasing clasp is desired, which
  equitably distribute the force between the abutment and the ridge;
     a) If a mesiobuccal undercut is available on the terminal abutment, a combination
     clasp with the wrought wire, back action, RPI, RPA clasps are used.
     b) If the retentive undercut is located on the distobuccal surface, a bar clasp, and
     the C clasp are used.
     c) If mesiolingual undercut is present a reverse back action clasp is used.


Evaluating the ability of a clasp arm to act as a stress-breaker,
       One must realize that flexing in one plane is not enough. The clasp arm must be
freely flexible in any direction, as dictated by the stresses applied. Bulky, half-round
clasp arms cannot do this, Round, tapered clasp forms offer advantages of greater and
more universal flexibility, less tooth contact, and better esthetics.
       Either the combination circumferential clasp, with its tapered wrought-wire
retentive arm, or the carefully located and properly designed circumferential or bar
clasp can be considered for use on all abutment teeth adjacent to the extension denture
bases if the abutment teeth are properly prepared, the tissue support is effectively
achieved, and if the patient exercises good oral hygiene.
Factors that control numbers of clasps used:
    (1) The amount of retention required by the denture depends on:
       a- Number teeth which be replaced.
       b- Displacing force.
       C- Patients need maximum stability.
    (2) The retention that provided by other methods than clasping.
    (3) The numbers of teeth available for clasping.
       The following rules apply for the number of clasps used:
       a) It is better to have too much retention than too little. (Clasps that prove to be
       unnecessary can easily be removed from the denture).
       b) The greater the number of clasps, the less will be the force applied.



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                                                                    PARTIAL DENTURE DESIGN

Keys to selecting a successful clasp design:
(1) Avoid direct transmission of tipping or torquing forces to the abutment;
(2) Accommodate the basic principles of clasp design by definitive location of
component parts correctly positioned on abutment tooth surfaces.
(3) provide retention against reasonable dislodging forces (with consideration for
indirect retention).
(4) Be compatible with undercut location, tissue contour, and esthetic desires of the
patient. It is most important single factor in selecting a clasp.
The placing of clasps:
  Clasps should be placed so that the direct retention they give is distributed as widely
  as possible.
  ► For class I partially edentulous arch, a bilateral clasping configuration is
  required.
  ► When two clasps are used an imaginary line drawn between them should divide
  the denture into two equal halves.
  ► If this (retention line) runs diagonally across an upper denture, it is considered
  an advantage for the resistant against the gravity displacement force.


III-Designing for bracing and reciprocation:
Bracing:
       It is the resistance to horizontal (lateral and antero-posterior ) movements of the
denture caused by lateral forces which occurred during:
1- Mastication as a component of the obliquely applied force.
2- Para function.

Resistance to lateral shifting is gained by:
     1- Maximum extension and coverage of the sides of the residual ridge with the
        denture base within the physiological limit.
     2- Rigid bracing clasp arms.
     3- Use of a continuous bar resting on the lingual surfaces of natural standing
        teeth (Kennedy bar).
     4- Rigid major and minor connectors
     5- The magnitude of the lateral forces may reduced by:
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                                                               PARTIAL DENTURE DESIGN

          - Reducing the steepness of the Cuspal angles of the teeth.
          - Reducing the size of the occlusal table.
          - Ensuring that the cusps are efficient during mastication.


Reciprocation:
      It is the resistance to horizontal forces exerted on a tooth by the retentive clasp
arm during insertion and removal of the RPD.
      This can be obtained by bracing clasp arm or plate contacting the tooth surface
while the movement of the retentive tips over the height of contour of the abutment.




Resistance of the antero posterior movement of the saddles:

             As there is a tendency of the upper denture to move forwards and the
          lower denture to move backwards, Resistance to anteroposterior
          movement is gained by:
           1. The presence of healthy well supported natural anterior teeth in the upper
              jaw and molar tooth or teeth in lower jaw.
           2. Covering the anterior slope of the hard palate, and the tuberosity.
           3. The use of posterior abutment.
           4. Steeply sloping mucosa in the retro molar region.




                                                                           Mostafa Fayad 11
                                                                        PARTIAL DENTURE DESIGN

                                   Stabilizing Components
- Stabilization is the resistance of partial denture to tipping forces.
Causes of tipping, rocking and rotation of RPD:
         1-      Different quality in the nature of the supporting structures
                 In tooth supported RPDs, the abutment teeth on both sides of the edentulous
                area provide adequate support and resistance to rotational forces through
                supporting rests and clasps placed on them.
                In Tooth-tissue supported distal extension partial dentures derive support from
                two different tissues. This results in vertical movement of the denture base either
                in tissue-ward or tissue-away direction when occlusal forces act on artificial
                teeth.
         2-      Sticky foods and muscle pull, acting on the periphery of the denture.
       3-    Intercuspation and occlusion of teeth
  Resistance to vertical and lateral tipping forces (rocking) is gained by:
          1. Adequate base coverage.
              2. The use of three, and if possible four, widely separated areas of tooth support
              3. Rigid bracing clasp arms
              4. Balanced occlusal contact and reduction of cusp slope.
              5. The use of additional rests serves as, indirect retainers.
              6. Coverage of the rugea area acts as an indirect retainer.
Stabilizing components of the removable partial denture framework are those rigid
components that assist in stabilizing the denture against horizontal movement.
              o minor connectors that contact vertical tooth surfaces
              o reciprocal clasp arms
Minor connectors
   •   should have sufficient bulk to be rigid
   •   Little bulk to the tongue as possible.
   •   Should be confined to interdental embrasures whenever possible.
   •   When minor connectors are located on vertical tooth surfaces, it is best that these
       surfaces be parallel to the path of placement.
   A modification of minor connector design has been proposed that places the minor
connector in the center of the lingual surface of the abutment tooth. Proponents of this design
claim that it reduces the amount of gingival tissue coverage and provides enhanced bracing
and guidance during placement. Disadvantages may include increased encroachment on the
tongue space, more obvious borders, and potentially greater space between the connector and
the abutment.

                                                                                   Mostafa Fayad 12
                                                                PARTIAL DENTURE DESIGN

Reciprocal clasp arms
       It must be rigid, and they must be placed occlusally to the height of contour of
the abutment teeth
       When crown restorations are used, a lingual reciprocal clasp arm maybe insert
into the tooth contour by providing a ledge on the crown on which the clasp arm may
rest. This permits the use of a wider clasp arm and restores a more nearly normal tooth
contour, at the same time maintaining its strength and rigidity.


Guiding Plane
       It is defined as two or more parallel, vertical surfaces of abutment teeth, so
shaped to direct a prosthesis during placement and removal.
       Guiding planes may be contacted by various components of the partial denture:
the body of an extracoronal direct retainer, the stabilizing arm of a direct retainer, the
minor connector portion of an indirect retainer, or by a minor connector specifically
designed to contact the guiding plane surface.
       The functions of guiding plane surfaces are as follows:
(1) To provide for one path of placement and removal of the restoration (to eliminate
detrimental strain to abutment and framework during placement and removal).
(2) To ensure the intended actions of reciprocal, stabilizing, and retentive components
(to provide retention against dislodgment of the restoration when the dislodging force
is directed other than parallel to the path of removal and also to provide stabilization
against horizontal rotation of the denture).
(3) To eliminate gross food traps between abutment teeth and the denture.
       Dimensions of guiding plane surfaces:
As a rule, proximal guiding plane surfaces should be about one half the width of the
distance between the tips of adjacent buccal and lingual cusps or about one third of the
buccal lingual width of the tooth. They should extend vertically about two thirds of the
length of the enamel crown portion of the tooth from the marginal ridge cervically.
       Guiding planes squarely facing each other should not be
prepared on lone standing abutment. Minor connectors of
framework (gray areas) would place undue strain on abutment when
denture rotated vertically either superiorly or inferiorly.

                                                                           Mostafa Fayad 13
                                                               PARTIAL DENTURE DESIGN



V-Designing for indirect retention:
  Methods of indirect retention:
  ► For distal extension bases (Class I and II) indirect retainers placed on the
  anterior part of the jaw are necessary.
  ► A class III denture whose saddles cannot, for some reasons, be clasped
  adequately may require anterior and posterior indirect retainers.
  ► Consequently, indirect retainers may be divided into those placed in the anterior
  and those in the posterior part of the mouth.
  - In the upper jaw either the teeth or the hard palate can be used to place an indirect
  retainer, whereas in the lower the teeth only can be used.
  ► Class IV dentures require an indirect retainer placed posteriorly to counteract a
  displacement of the anterior saddle away from the ridge
   - The forms of indirect retention shown in the following table are popular types:




       Contrary to common use, a cingulum bar or a linguoplate does not in itself
act as an indirect retainer. Because these are located on inclined tooth surfaces, they
serve more as an orthodontic appliance than as support for the partial denture. When a
linguoplate or a cingulum bar is used, terminal rests should always be provided at
either end to stabilize the denture and to prevent orthodontic movement of the teeth
contacted. Such terminal rests may function as the indirect retainers,




                                                                          Mostafa Fayad 14
                                                               PARTIAL DENTURE DESIGN

VI- Designing the connector:
   Types of maxillary major connector:
   1- Single palatal bar.
   2- Anteroposterior or double palatal bar.
   3- Single palatal strap.
   4- Horseshoe or U-shaped palatal bar.
   5- Closed shoe or Anteroposterior palatal strap.
   6- Complete palatal plate.
   Types of Mandibular major connector:
   1- Lingual bar.
   2- Sublingual bar.
   3- Double lingual bar.
   4- Lingual plate.
   5- Labial bar.


VII-Minor connectors:
   Design considerations:
   -it should be ensuring that there is 5 mm of space between adjacent vertical minor
   connectors to prevent food impaction.
   - must contact the guiding plane surfaces of the teeth to facilitate path of insertion
   and provide bracing.
   -should cross the gingival tissue abruptly and join the major connector at rounded
   right angles. These allow them to cover as little as possible of the gingival tissues.
VIII- Esthetic:
          The function and esthetics of removable partial denture are dependent on
   the correct orientation of the occlusal plane. The main esthetic problem is the
   presence of visible retainers in the buccal vestibule. Rotational path partial
   denture may be used to improve esthetic




                                                                           Mostafa Fayad 15
                                                                PARTIAL DENTURE DESIGN




ADDITIONAL CONSIDERATIONS INFLUENCING DESIGN

Use of a Splint Bar for Denture Support

a removable partial denture should replace only the missing posterior teeth after the
remainder of the arch has been made intact by fixed restorations.

Occasionally, it is necessary that several missing anterior teeth be replaced with the
RPD rather than by fixed restorations. This may be because of

   •   The length of the edentulous span,

   •   The loss of a large amount of the residual ridge by
       resorption,

   •   Accident or surgery,

   •   The result of a situation in which too much vertical space
       prevents the use of a fixed partial denture or

   •   If esthetic requirements can better be met through using of teeth added to the
       denture framework.

       It is necessary to provide the best possible support for the replaced anterior
   teeth. Ordinarily, this is done through the placement of occlusal or lingual rests, or
   both, on the adjacent natural teeth, but when the edentulous span is too large to
   ensure adequate support from the adjacent teeth, other methods must be used.

       An anterior splint bar may be attached to the adjacent
   abutment teeth in such a manner that fixed splinting of the
   abutment teeth results, with a smooth, contoured bar resting
   lightly on the gingival tissue to support the RPD. the
   connecting bar may be cast of a rigid alloy, or a
   commercially available bar may be used and cast to the abutments or attached to
   the abutments by soldering. The length of the span influences the size of a splint
   bar. Long spans require more rigid bars (10 gauge) than short spans (13 gauge).

       The proximal contours of abutments adjacent to splint bars should be parallel to
   the path of placement. The splint bar must be positioned antero posteriorly just
   lingual to the residual ridge to allow an esthetic arrangement of artificial teeth.


                                                                            Mostafa Fayad 16
                                                            PARTIAL DENTURE DESIGN




   Internal Clip Attachment

   The internal clip attachment differs from the splint bar in that the internal clip
attachment provides both support and retention from the connecting bar.

   Several preformed connecting bars are commercially available in plastic
patterns. These can be customized for length and cast in the metal alloy of choice.
Internal clip attachments are also commercially available in various metal alloys
and durable nylon.

   The cast bar should rest lightly or be located slightly above the tissue. Retention
is provided by one of the commercial preformed metal or nylon clips, which is
contoured to fit the bar and is retained in a preformed metal housing or partially
embedded by means of retention spurs or loops into the overlying resin denture
base. The internal clip attachment thus provides support, stability, and retention for
the anterior modification area and may serve to eliminate both occlusal rests and
retentive clasps on the adjacent abutment teeth.

   Overlay Abutment (Overdenture abutments and overlay-type prostheses)

   Indications:

   1- When salvage the roots and a portion of the crown of a badly broken-down
    molar through endodontic treatment.

   2- A periodontally involved molar, indicated for extraction, may sometimes be
    salvaged by periodontal and endodontic treatment accompanied by reduction
    of the clinical crown almost level with the gingival tissue.

   3- An unopposed molar may have extruded to such an extent that restoring the
    tooth with a crown is inadequate to develop a harmonious occlusion.

   4- A molar that is so grossly tipped anteriorly that it cannot serve as an
    abutment unless the clinical crown is reduced drastically.




                                                                       Mostafa Fayad 17
                                                            PARTIAL DENTURE DESIGN

          In these cases, teeth should be considered for possible support.
    Endodontic treatment and preparation of the coronal portion of the tooth as a
    slightly elevated dome-shaped abutment should be done.

   Use of a Component Partial to Gain Support

   A component partial is a removable partial denture in which the framework is
designed and fabricated in separate parts. The tooth support and tissue-supported
components are individually fabricated, and the two are joined with a high-impact
acrylic resin to become a single, rigid functioning unit.




                                                                     Mostafa Fayad 18
PARTIAL DENTURE DESIGN




         Mostafa Fayad 19
                                                               PARTIAL DENTURE DESIGN




            Designing Removable Partial Dentures
              Problems and General Principles
             1- Kennedy Class I Partial Dentures

It is More frequent in lower than upper jaw

Problems associated with bilateral free-end saddles :

       1- Lack of posterior abutment is usually associated with lack of adequate
           posterior support and retention.
       2- Support is derived from both the residual ridge and abutment teeth. The
           variation in displaceability providing this support allows some rotational
           movements of the free-end base towards the soft tissues. These harmful
           movements are transmitted to abutment teeth resulting in loosening of these
           teeth.
       3- Major support is obtained from the residual ridge especially at the distal part.
           This causes frequent residual ridge resorption.
       4- If resorption occurs and relining of the denture is neglected further bone
           resorption occurs with subsequent torque acting on the abutments.
       5- Stability.
       6- The need for indirect retainers.
       7- Esthetic.

       Possible rotational movements of distal extension bases:
       • Rotational about the fulcrum axis formed by the two principle occlusal rests.
       • Rotational movement along the longitudinal axis of the residual ridge.
       • Rotational movement along perpendicular axis passing through the centre of
           the arch.




                                                                           Mostafa Fayad 20
                                                             PARTIAL DENTURE DESIGN




Factors influencing the support of a distal extension base:
         Support of a distal extension partial denture depend on :
       1-Total occlusal load applied
                   The more the load applied the higher the degree of tissue
            displacement.
               The reduction of the size of the occlusal table reduces the vertical
            and the horizontal force. Increase the efficiency of the occlusal surface
            of the artificial teeth by addition of supplementary groves & sluice ways
            increase in cutting action & improve the masticatory performance of the
            teeth. This leads to less force required in chewing and less force will
            then be transmitted to the residual ridge. All these actions help improved
            the support for the denture base.
       2- Quality of the residual ridge.
            o      Quality of soft tissues covering the edentulous ridge.
            o      Contour and quality of the residual ridge
            o      Denture bearing area.
                   Easily displaceable tissue will not adequately support a denture
            base. The thicker the mucoperiosteum the more it is liable to be
            displaced. A firm, tightly attached mucosa, several mm thick, will give
            greatest support.
       3-Extent of residual ridge coverage by the denture base
            The broad the coverage, the greater is distribution of the load, thereby
            resulting in fewer loads per unit area.
       4-Accuracy of the fit of the denture base
            The better the base fits the denture foundation the less the degree of
            displacement. Metal bases have better fit than acrylic resin bases.
       5-Type (anatomical or functional) and accuracy of impression registration
            against which the denture bases are fabricated
            When an appliance is entirely tissue supported mucosa, tissue-ward
            movement of the appliance will take place, to the degree that the tissue
            will be displaced by pressure (tissue rebound). Minimization of tissue

                                                                       Mostafa Fayad 21
                                                               PARTIAL DENTURE DESIGN

              ward movement of the partial denture can be accomplished by wide
              coverage.
         6- Design of the partial denture Framework
                     The rotation forces take place around the fulcrum line can be
             controlled by using of indirect retainers anterior to the fulcrum line. If
             the distal extension denture is bilateral two indirect retainers are needed
             one on each side of the arch. If the edentulous space is unilateral only
             one indirect retainer is needed anterior to the fulcrum line on the
             opposing side of the arch from the distal extension ridge.

        7- Denture- bearing area:

                  In the maxillary arch: - The buccal slopes of ridge, normally covered
             by a layer of cortical bone can withstand stress. But the buccal slope is
             rarely perpendicular to the vertical force occurring against it, so it gives
             little resistance to them. However the buccal slope will resist the lateral
             forces, reducing the total force.

                In the mandibular arch:- the crest of the ridge can't be used as a
             primary stress bearing area, because it's composed of cancelous bone,
             covered by thin & less firm mucosa. The buccal shelf area is excellent
             primary stress bearing area in the mandible, because it is very dense
             cortical bone covered by firm & dense mucosa. The buccal shelf area is
             normally perpendicular or nearly so, to the vertical force would be
             occurring against it. The buccal & lingual slopes of the residual ridge
             have cortical bone and can contribute to resisting horizontal forces.




Problems of distal extension bases can be reduced by :
I. Controlling the load applied on abutment and residual:
I- Reduction of the load.
II- Distribution of load can be achieved by:
     1- Varying the connection between the clasps and saddles:


                                                                          Mostafa Fayad 22
                                                                PARTIAL DENTURE DESIGN

            A-Applying the stress-breaking principle
            b- Combining rigid connection and flexible clasps
           c. Combining rigid connection and rigid clasps. (↑load on the tooth)
      2- Anterior placement of occlusal rests
       3- Improving the supporting quality of edentulous ridges:
            - Improving the condition of the residual ridge
            - By muco-compression impression techniques
III- Wide distribution of the load.
IV- Providing posterior abutments.
     1- Using an implant at the distal part of the ridge.
      2- Salvaging a hopeless posterior tooth.
II. Enhancing support by
1- Converting the case to:
      A. Removal partial overdenture using endosseous implant in each side.
      B. Fixed bridge connecting endosseous implant to the posterior tooth.
      C. Fixed bridge connecting two endosseous implants in each side.
2- Ridge augmentation
3- Splinting of abutment
4- Improving the supporting quality of edentulous ridges:
            - Improving the condition of the residual ridge
            - By muco-compression impression techniques
III. Achieving good stability: Using Rigid Major & Minor Connectors
IV. Using Indirect retainers
V. Using esthetic retainers

I- Reduction of the load

       The vertical load applied on the saddle during mastication should be reduced in
order to minimize vertical displacement of the denture base. The vertical load may be
reduced by decreasing the size of the occlusal table and by maximum extension of
the denture base within the functional limits of muscular movements.

This can be achieved by:

                                                                         Mostafa Fayad 23
                                                               PARTIAL DENTURE DESIGN

   1- Using canines and premolars instead of premolars and molars.

   2- Using narrow teeth (bucco-lingually) or reduction of the width of the selected
      teeth by removing the lingual cusps.

   3- Leaving a tooth off the saddle.

   4- Increase the sharpness of the cusps.

   5- Increasing efficiency of the occlusal surface of the artificial teeth by addition of
      supplemental grooves aids the cutting action and improve masticatory
      performance of the teeth.



II- Distribution of the load between abutment teeth and ridge



Distribution of load can be achieved by:

   1) Varying the connection between the clasps and saddles:

a-Applying the stress-breaking principle

      Movement of the denture base over displaceable mucosa will be transmitted to
   the abutment tooth if the tooth is connected to the denture base by a rigid
   connector. These stresses will induce torque on* the abutment. However, these
   stresses will be dissipated if some flexibility is allowed. The stress breaking
   principle will thus apply less stresses and less torque on abutments.

   Stress breakers:

      A stress breaker or stress equalizer is a device which allows movement between
   the saddle unit and the retaining unit.

      Thus, when a vertical load is applied, the stress breaker will allow movement of
   the saddle towards the ridge to a greater extent than if the retainer unit is directly
   connected to the saddle, although the ridge bone will be subjected to an increased
   load. However, this load is widely distributed antero-posteriorly over the ridge and
   not on the distal part only. Also flexibility of the stress breaker can be changed to
   govern the distribution of load between the ridge aril abutments.

Stress breakers may be in the form of:

   •   Movable joints as hinges between the saddle unit and the retaining unit. e.g.
       attachments like Dalbo or Crisimany attachments,



                                                                           Mostafa Fayad 24
                                                                PARTIAL DENTURE DESIGN

   •   Designs applying the stress breaking principle used in combination with the
       main rigid connector (using flexible connection between the direct retainer and
       the denture base ).{for detail see stress breaker}

   -    Split major connector ( Split casting modifying the lingual plate)

   -    Wrought wire connector soldered to lingual bare.

   -    Lingual bar connector with flexible distal extension (having thinner section
       than lingual bar (use of semi-flexible bar).

   -    Disjunct RPD.

b- Combining rigid connection and flexible clasps (stress releasing clasps)

    Flexible gingivally approaching clasps (bar clasps)

       The retentive tip of gingivally approaching clasps contacting the abutment
    tooth' originates from the saddle in the form of a bar. The degree of flexibility of
    the bar can be varied depending on its length, diameter, cross section and die alloy
    used. Thus a flexible bar may move gingivally into the undercut which in turn
    dissipates some of the stresses falling on the abutment tooth.

      Thus, bar clasps apply the stress-breaking principle. I-bar, RPI clasps are
    examples of gingivally approaching clasps that provide a stress breaking effect
    when a rigid connector is used in distal extension bases.

    Flexible occlusally approaching clasps

      Occlusally approaching clasps can be used in distal extension bases when a
    wrought wire retentive arm is used instead of a cast clasp arm.

       The resilient wrought wire arm allows some movement of the clasp over the
    tooth, thus following the stress breaking principle. Back-action clasps are also
    used in distal extension bases due to their stress breaking effect. It should be noted
    that excessive resiliency is not favorable because it results in an unretained
    denture.

    Flexible combination clasps

c. Combining rigid connection and rigid clasps.

It can be rarely used in young age, will developed ridge, and very short saddle.

Clasps with Stress breaker action as:

1. Gingivally approaching resilient I-bar clasp.


                                                                           Mostafa Fayad 25
                                                                 PARTIAL DENTURE DESIGN

2. Occlusally approaching clasp having resilient retentive wrought gold wire arm
(Combination clasp).

3. Back-action clasp.

4. Reverse back-action clasp.

5. Extended-arm clasp.

6. Ring clasp.

7. Wrought wire clasp.

8. RPI clasp.

9. RPA clasp.

2) Anterior placement of occlusal rests:

       Placement of the occlusal rest in a more anterior position helps in favorable
distribution of occlusal load between the abutment tooth and the residual ridge.

   •   The farther the anterior placement of the rest, the more vertical will be the
       forces, the less is the horizontal component of force falling on the ridge,

    The rest proximal plate, I bar clasp (RPI) and the reverse circlet clasps have
     mesially located rests which can fulfill this requirement,

Advantages:

   •   Achieving a mechanical advantage by changing the stresses acting on the
       saddle from a .class I lever to a more favorable class II lever

   •   Greater part of the occlusal load will be borne by the ridge and hence less
       stresses and less torque on the abutment.

   •   Even distribution of the load 'in an antero-posterior direction. The bone near the
       abutment will thus share the distal part of the ridge in bearing the occlusal load,

   •   Changing the direction of torque on the abutment from the distal to the mesial
       side of the tooth where resistance to torque action will be supplied from the
       neighbouring teeth.

   Disadvantages:

   •   Wedging effect

   •   Food impaction between distal surface of abutment and RPD.

   - the RPI System.                      - The Balance of force system.!! !!!!! !

                                                                              Mostafa Fayad 26
                                                             PARTIAL DENTURE DESIGN



3) Improving the supporting quality of edentulous ridges:
   -   Improving the condition of the residual ridge
   -   By Functional impression techniques
   -   Functional impression techniques:

    McLean’s physiologic impression (done at the master impression stage)
    Hindels' physiologic impression (done at the master impression stage)
    Functional denture base: Functional relining and fluid wax impression
     techniques.
    Selective pressure impression technique.

III- Wide Distribution of Load

       Distribution of the occlusal load widely is effective in reducing the force per
unit area on the residual ridge.

1- Wide distribution of the load over the ridge.

The denture base should cover the largest possible area and should be adequately
extended to the functional limit of the surrounding musculature. The broader the
coverage, the greater the distribution of load, the more the ability of the denture to
withstand vertical and horizontal stresses.

2- Wide distribution of load over the teeth:

       Distribution of the vertical load on teeth can be achieved by placing an
additional rest on the tooth adjacent to the abutment, by an embrassure clasp,
embrasure hooks or by splinting. Using a Kennedy bar to distribute the lateral load on
multiple teeth.

IV- Providing Posterior Abutments

       The problem of distal extension bases can be solved by provision of
posterior5ahujtrnents and construction of a partial oeverdenture. This can be achieved
by:

1- Using an implant at the distal part of the ridge.

2- Salvaging a hopeless posterior tooth.

       A hopeless badly decayed tooth, a periodontally affected tooth or a tooth with
furcation involvement can be reduced in both contour and height to be used as a partial
overdenture abutment.

V- Functional impression

                                                                         Mostafa Fayad 27
                                                                PARTIAL DENTURE DESIGN

       The normal mucosa covering the ridge can be recorded in its displaced
functional form rather than the anatomic form. This reduces movement of the denture
base towards the tissues during function, which in turn helps in reducing leverage and
torque on the abutment teeth.

However, maximum displacement of the mucosa should be avoided. This is because
when the mucosa is subjected to heavy continuous pressure, a decrease in the blood
supply and drainage from soft tissues occur, resulting in pain under the denture,
atrophic changes and future bone resorption.

VI-Improving the supporting quality of edentulous ridges

- Improving the condition of the residual ridge

       The presence of a well formed residual ridge covered by healthy firm mucosa,
provides favorable partial denture support. However, the presence of tori or
hyperplasic tissues necessitates correction to improve the supportive ability of the
ridge.

VII- Using esthetic retainers

Numerous esthetic clasp systems are available for distal extension RPD.These clasps
can either utilize the proximal, lingual, labial or buccal retentive undercut.

Examples: Mesiodistal clasp, the De-Van clasp, the Equipoise clasp and twin Flex
clasp

           Class I partially edentulous cases when the remaining teeth are weak,
            periodontally affected, and require splinting and stabilization are
            sometimes treated using swing-lock partial dentures.

           Anterior modification spaces of class I cases, are preferably restored
            separately with a fixed bridge. This helps in simplifying the partial
            denture design and also helps in saving the anterior ridge from resorption
            and the anterior abutments from torque. Possible solutions 1.Extraction
            of weak abutment. 2. Removable partial overdenture.3. Splinting by
            fixed bridge and conventional RPD. 4. Addititional saddle to the lingual
            bar with using wrought wire clasp and no occlusal rest on the single
            standing tooth.



MAXILLARY BILATERAL FREE END SADDLES

1) Under vertical load the posterior sink of the saddle is less marked due to:
     - The submucosa covering the tuberosity has dense fibres than retromolar area.
                                                                           Mostafa Fayad 28
                                                             PARTIAL DENTURE DESIGN

     - Extra palatal coverage >>>> reduce displacement under load
2) Lateral load is shared over a great area of bone (palate) and hence the lateral load
falling on the abutments is less than lower
3) Anteroposterior movement is prevented by: Standing teeth Anterior slope of palate
Tuberosity




               Kennedy Class II Partial Dentures
Problems associated with a unilateral free-end saddle:
1- Class II partial dentures have problems resulting from the absence of a posterior
   abutment which causes lack of proper posterior support and retention.



                                                                         Mostafa Fayad 29
                                                               PARTIAL DENTURE DESIGN

    • Being tooth-tissue borne, the difference of displaceability of the supporting
    tissues results in tissue ward movement of the denture base with subsequent torque
    on the abutment tooth.
    • Lack of adequate posterior retention causes displacement of the denture away
    from the tissues with subsequent torque on the' abutment.
2- The absence of a saddle on the other side of a class II partial denture
   complicates the retention of the appliance. This is due to decrease in the physical
   means of retention and due to the lack of the retentive effect of the tongue and
   cheek muscles that would rather act in the presence of a modification area on the
   other side.

The main problem: is the same as with the bilateral free-end saddle denture including:
a) Torque of abutment.
b) Ridge resorption.
         Management: as Class I-Kennedy RPD.
c) The problem of retention (similar saddle is not present on the other side)
         Management: Additional retention must be provided on the intact side by:
                  - Clasping more than one tooth on this side
                   - More rigid types of clasp.
b) The problem of bracing (due to absence of rigid major connector)
          Management:
                       - Cross-arch bracing (Through a rigid major connector).
                       - Bracing components.




Problems of unilateral distal-extension bases can be reduced by:
    • Load reduction and distribution.
    • Provision of adequate posterior support.

                                                                           Mostafa Fayad 30
                                                               PARTIAL DENTURE DESIGN

    • Using an indirect retainer to counteract rotation of the denture in an occlusal
    direction.
    • Providing adequate retention on the dentulous side by using rigid clasping or
    multiple clasping on the intact side.
    • Providing posterior abutment using an implant at the posterior part of the ridge
    and the construction of an implant supported partial overdenture.

Designing class II partial dentures:
       Designing class II partial dentures usually follow the same basic principles.
However, some modifications of the design are required depending on the length of
the saddle and the presence of modification areas.
I- Designing class II partial dentures with no modifications:
              Divided into two groups depending on:
               The nature of the edentulous ridge,
               The length of the edentulous ridge and
               The condition of the abutment.
   Two basic designs can be followed in unmodified class II partial dentures
1- Designs using rigid clasping and rigid connection between the saddle and the
   retainer. (Rigid design)
        This design is indicated in:
        a- Short edentulous span bounded ,
        b- Cases having well formed edentulous residual ridge covered with firm
        mucosa of normal thickness.
        c- strong abutment with healthy periodontium.
2- Designs applying the stress breaking principle. (flexible design)
      A class II partial denture design may require a stress breaking effect when the
   condition of the abutment, the length of the saddle and the compressibility of the
   mucosa contra-indicate the use of rigid clasping and rigid connection.

      An embrasure clasp is usually used on the dentulous side. An indirect retainer
should be provided to counteract rotation of the denture away from the tissues.

       Designs applying the stress breaking principle:

   -    The use of semi-flexible bar: This is more applicable with shot saddles, it
        involves anterior placement of an occlusal rest.
                                                                        Mostafa Fayad 31
                                                                 PARTIAL DENTURE DESIGN

                  1- The occlusal rest is placed on the far zone of the abutment tooth.

                  2- The abutment is rigidly clasped, and joined to the clasp onto the
                     opposite dentulous side by a rigid connector (lingual bar).

                  3- The saddle is joined to the retainer unite by a semi-flexible bar
                     that allows some movement and provides stress breaking action.

                  4- An embrasure clasp is usually used on the dentulous side. (used
                     with short saddle)

   -   Split casting modifying the lingual plate: a split of appropriate length is made at
       the inferior border of the plate.

                  1- The saddle is joined to the more flexible part of the plate. The
                     lower part must be flexible in the vertical direction, than
                     horizontal direction, so that the appliance will have lateral rigidity
                     to distribute horizontal force widely.

                  2- This design applied in long class II cases. (used with long saddle)

                  3- Disadvantages : The slit opens slightly in function and
                     theoretically is liable to trap either the tongue or food particles.
                     With a long saddle, however, the slit is anteriorly placed and in
                     this position may be intolerable to some patients. The patient
                     using dental floss can clean the slit easily.




II- Class II with modification spaces:
       The presence of modification spaces on the opposite side of a Kennedy class II
simplifies the partial denture design. The problem of retention is solved by the
presence of saddles on the modification areas. The clasps on abutments bounding
the modification area provides retention, bracing and reciprocation together with
indirect retention,

                                                                            Mostafa Fayad 32
                                                                PARTIAL DENTURE DESIGN

       Retention on the side of the bounded saddle is dependent upon the ability of the
single molar tooth to withstand the loads applied; therefore:
       i. If the periodontal condition of such a single standing tooth is good, rigid
construction is employed and frequent inspection of the appliance is essential so that
rebasing may compensate resorption under the free-end saddle. If this is not done, a
damaging torque will be applied to the single standing molar leading at least to
increased tilting and at worst to loosening and eventual loss.
        ii. If the periodontal condition of such a single standing tooth is doubtful, it
may be possible to design the denture incorporating a flexible connector to the distal
extension saddle as already described. In addition less stress will be applied to the
tooth if wrought wire instead of cast metal is used for clasp construction.


THE MAXILLARY UNILATERAL FREE-END SADDLE DENTURE
          •   Unmodified maxillary unilateral free-end saddle dentures are not
              common.
          •   Those with modifications are encountered frequently due to the loss of
              teeth due to caries, and hence a well-formed ridge is present.
                     • Rigid constructions are almost always.
                     • Clasping of the abutment tooth (Flexible clasping) and suitable
                     teeth on the opposite side.
                     • If for any reason complete palatal coverage with a plate is used,
                     clasping may be unnecessary
          •   As with bilateral free-end saddles the single standing premolar may be a
              complication.




                                                                          Mostafa Fayad 33
                                                                        PARTIAL DENTURE DESIGN

                     A ] Essentials of Design for Classes I and II
1- Direct retention

   Retention should not be considered the prime objective of design. The main objectives
should be the restoration of function and appearance and the maintenance of comfort, with
great emphasis on preservation of the health and integrity of all the oral structures that
remain.

   Close adaptation and proper contour of an adequately extended denture base and
accurate fit of the framework aga- inst multiple, properly prepared gulde planes should be
used to help the retentive clasp arms retain the pros- thesis.

2- Clasps

a- The simplest type of clasp that will accomplish the design objectives should be employed.

b- The clasp should have good stabilizing qualities, remain passive until activated by
  functional stress, and accommodate a minor amount of movement of the base without
  transmitting a torque to the abutment tooth.

c- Usually stress releasing designs are preferred.

         Stress director attachments.

         Wrought wire clasps. RPI, I-bar, combination clasps, back action, reverse back action
          or reverse circlet clasps can be used.

         Remote rest and other conventional clasps.

         Split major connectors - permit more rigid clasp designs.

d- Clasps should be strategically positioned in the arch to achieve the greatest possible control of
  stress.

Class I prosthesis usually requires only two retentive clasp arms: one on each terminal tooth.

   If   a disto-buccal undercut is present, the vertical projection retentive clasp is preferred.

   If   a mesio-buccal undercut is present, a wrought wire clasp is indicated.

   Thereciprocal or bracing arm must be rigid. This component of the clasp system can be
   replaced by lingual plating.

Class II prosthesis should usually have three retentive clasp arms.

   The distal extension side should be designed with the same considerations as for a
   class I prosthesis.



                                                                                    Mostafa Fayad 34
                                                                    PARTIAL DENTURE DESIGN

  The tooth supported, or modification, side should usually have two retentive clasp
  arms : one as far posterior and one as far anterior as tooth contours and esthetics permit.
  If a modification space is present, it is usually most convenient to clasp a tooth anterior
  and a tooth posterior to the edentulous space.

   - The type of clasp and position of the retentive undercut can be selected for
     convenience.

   - Rigidity is required for all bracing arms. Lingual plating may be substituted.

    Stress releasing clasps
    a- Clasps with mesial rest

    - RPI     - RPA

    - Combination clasps

    b- Clasps with distal rest

    - Wrought wire clasps. - I-bar

    - Back action            - Reverse back action

    - Reverse circlet clasps - c-clasp



3- Rests

  Rest seats should be prepared so that stress will be directed along the long axis of the
  teeth.

     Although adjacent (proximate) rests may provide efficient force transmission to
  abutment teeth, remote rest clasp designs are often more desirable since they may
  decrease unfavourable torquing forces on abutment teeth from clasps.

  Rest seats should be carefully located and prepared to avoid torque and allow
  transmission of stresses along the long axes of abutment teeth.

  The floor of the rest seat should inclined apically as it approaches the center of the
  tooth. The angle between the minor connector and the rest should be less than 90˚ to
  prevent slippage of the prosthesis creating an orthodontic like force and to direct the
  forces along the long axis of the tooth.

  Mesially placed rests are preferably used on abutment teeth. However, absence of a
  rest adjacent to the edentulous area may permit packing of food. This could be avoided
  by using .



                                                                                 Mostafa Fayad 35
                                                                          PARTIAL DENTURE DESIGN

      Saucer-shaped rest seats are preferred over box shaped seats to avoid locking of the
      rest and transmission of torque on abutments.

      The occlusal rest must fit the tooth to minimize the food collection beneath it and
      preserve their location in relation to the tooth.

        It must be strong enough to withstand the loads without deformation.

        It must not raise the vertical dimension of occlusion.

4- Indirect Retention

1.    Indirect retention should be employed to neutralize unseating forces.

     The indirect retainer should be located as far anterior to the fulcrum line as possible.

     Two indirect retainers should generally be used in a class I design, whereas one placed on
      the side opposite the distal extension base may be adequate in a class II- design.

     The indirect retainers should be positioned in teeth prepared with positive rest seats that
      will direct forces along the long axis of the tooth.

2. Lingual plating can be used to extend the effectiveness of indirect retention to several
 teeth. It must always be supported by positive rest seats.



5- Major connector

a- The simplest connector that will accomplish the objective should be selected.

 1- The major connector must be rigid.

 2- Promotes cross-arch force transmission (contributes to cross arch stability and support)

 3- It must not impinge on gingival tissue.

b- Support from the hard palate should be used in the design of the maxillary major
   connector when it would be beneficial.

c- Extension of the major connector onto the lingual surfaces of the teeth may be employed
   to increase rigidity, distribute or eliminate potential food impaction areas. Lingual plating
   should always be supported by adequate rest seats.

d- Antero posterior palatal bars and palatal plates are preferred for maxillary class I cases to
   provide maximum support, direct and indirect retention.

e- For mandibular class I cases, lingual bars with terminal rests are preferred due to their
   simplicity, limited coverage and patient's tolerance. However, mechanically, lingual plates



                                                                                       Mostafa Fayad 36
                                                                              PARTIAL DENTURE DESIGN

  with terminal rests are biologically preferred due to their rigidity, distribution of lateral
  forces and due to improved indirect retention.

6- Minor connectors

   1.   Minor connectors must be rigid.

   2. Minor connectors should be positioned to enhance comfort, cleanliness, and the
   placement of artificial teeth.

7- Proximal plates (guiding Plates)

  -Guiding planes are flat axial parallel surfaces in an occluso-gingival direction on the
            proximal or lingual surfaces of teeth. They are 2-4 mm in height، extending from
            the marginal ridge to the junction of the middle and gingival third of the
            abutment tooth. The bucco-lingual width of the proximal plate is determined by
            the proximal contour of the tooth.

        -For bounded base a well-engineered guiding planes are contacted by the truss arms
            of the framework as the prosthesis is inserted and removed, thus horizontal
            wedging is virtually eliminated.

        -In distal extension base a pronounced guiding plane is not recommended

               -The proximal plate minor connector is placed on a distal guiding plane. It
                  should contact approximately 1 mm of the gingival portion of the guiding
                  plane in distal extension cases. The interface between the tooth surface
                  and the clasp should be such that a slight degree of movement of the base
                  and the clasp is permitted without transmitting torsional stress to the
                  tooth.

                -The proximal plate together with the mesiolingually placed minor connector
                  provides stabilization and reciprocation of the assembly.




  Guiding plane surface should be like area of cylindrical object It should be continuous surface
   unbounded by even rounded line angle. B, Minor connector contacting guiding plane surface has
   same curvature as does that surface. From occlusal view it tapers buccally from thicker lingual
   portion, thus permitting closer contact of abutment tooth and prosthetically supplied tooth. Viewed
   from buccal aspect, minor connector contacts enamel of tooth on its proximal surfaces about two-
   thirds its length.




                                                                                            Mostafa Fayad 37
                                                                                PARTIAL DENTURE DESIGN




        Diagrammatic illustration showing comparative width of the proximal plates for differently
        contoured teeth. (A). Proximal plate (p) relatively wide due to the square contour of the 2nd
        bicuspid. (B). Proximal palate (p) relatively narrow due to the tapering contour of the 1st
        bicuspid. The proximal plate should be designed as narrow as possible but should prevent lingual
        migration of the tooth. A narrow proximal plane permits greater exposure of the gingival tissue
        (g).

8- Occlusion

1.Centric   occlusion and centric relation should be coincide.

2.A harmonious occlusion should be established with no interceptive contacts and with all
  eccentric movements dictated by, or in harmony with, the remaining natural teeth.

           teeth should be selected and positioned to minimize stresses produced by the
3.Artificial
  prosthesis.

   Smaller and/or fewer teeth, and teeth that are narrower bucco-lingually may be selected.

   For mechanical advantage teeth should be positioned over the crest of the mandibular
    ridge when possible.

   Teeth should be modified if necessary to produces sharp cutting edges and ample
    escape-ways.

9- Denture base

1.The   base should be designed with broad coverage so that the occlusal stresses can be
  distributed over as wide an area of support as possible. The extension of the borders must
  not interfere with functional movements of the surrounding tissues.

2.Aselective pressure impression should record the residual ridge in a functional form. Or it
  may be constructed in the static form if the stress breaking principle is applied.

3.The polished surfaces should be contoured to enable the patient to exercise maximum
  neuromuscular control.

4. A combined metal-acrylic base is used to allow for future relining as bone resorption is
  usually anticipated.

Recontouring

The contours of the natural teeth most often require adjustments for the proper placement
and functioning of the RPD.


                                                                                               Mostafa Fayad 38
                                                                  PARTIAL DENTURE DESIGN

    Recontouring may be required to

           1. Improve survey lines (improve clasp loca   on),

           2.Improve clasp reten    on (dimpling)

           3.Improve the occlusal plane by grinding of the cusp tips and incisal edges of
           anterior teeth.

    Excessive tooth contours are reduced by lowering the height of contour so that;

           1. The origin of the circumferential clasp is placed preferably at the junction
              of the middle and gingival third of the crown

           2. The retentive terminal is placed in the gingival third of the crown for
              better esthetics and better mechanical advantage.

           3. The reciprocal clasp is placed above the height of contour, but not higher
              than the cervical portion of the middle third of the crown.




                Kennedy Class III Partial Dentures
Problems associated with unilateral bounded saddles:

      Two opinions exist to restore short edentulous space by removable partial
dentures.

1- Restoring a single tooth or a short span unilateral area is not practical especially in
cases having bad oral hygiene and caries susceptibility.

2- Restoration of any missing tooth is necessary in order to: -Restore the integrity of
the dental arch, prevent tilting, drifting, rotation or overeruption of the remaining
natural teeth.

- Restore the masticatory mechanism.

- Restore aesthetics.

Restoration of the unmodified class III: (Unilateral bounded areas)

I - Implant retained restoration

II - Fixed bridges:
      Fixed bridges are usually the treatment of choice for short span bounded
edentulous areas when:

                                                                              Mostafa Fayad 39
                                                                PARTIAL DENTURE DESIGN

-   Implant retained restoration is contraindicated.

-   Abutments are strong and healthy

-   Aesthetics is of great concern.

-   Minimum bone loss exists.

-   The oral hygiene is good.

III - Unilateral partial dentures (side plates or removable bridges):
       Unilateral partial denture is constructed to restore one side of the arch and not
extended to the other side. This prosthesis has less retention and stability, permits
limited load distribution and is unsafe to use due to the probability of being inhaled or
swallowed.

The following measures are used to avoid instability of unilateral partial
dentures:

    a- Provision of lingual and buccal cusp contacts on the working side in lateral
       movement.

    b- Maximum extension of the rest seat preparation and the occlusal rest especially
       to the buccal side. This keeps the axis of rotation as far buccally as possible and
       ensures transmission of vertical component of force lingual to this axis.

    c- Providing adequate bracing against lateral movement especially buccal
       movement. This can be achieved by:-

          - Extending the denture base on the vertical slope of the hard palate.

          - Bracing arms located on the abutment tooth and the tooth adjacent to it.

          - Clasping adjacent teeth to allow wider load distribution laterally.

          - Using box shaped rest seat preparation to increase bracing.

    d- Providing adequate retention against both vertical and buccal displacement.
       This can be achieved by using clasps that provide both buccal and lingual or
       palatal retention i.e. a clasp with bilateral bracing and retention.

Contra indications of unilateral partial dentures:

    Unilateral partial dentures are contra indicated in the following cases:

    - Patients employing excessive lateral movement during mastication.

    - Patients exhibiting bruxism.


                                                                            Mostafa Fayad 40
                                                                PARTIAL DENTURE DESIGN

    - Conical shaped abutment teeth, weak teeth, or teeth having short crowns that
    cannot provide adequate retention and bracing.

    -   In old patients.

IV - Bilateral partial denture:

       A partial denture restoring a unilateral bounded edentulous area is extended to
the other side of the intact arch . Bilateral removable partial dentures provide better
retention and stability together with wider load distribution.

Bilateral class III partial denture design:

1-Denture base:

        The denture base is designed to fit the static rather than the functional form of
the ridge because the denture base is adequately supported on both sides by abutment
teeth, i.e. tooth supported.

Metal plates are usually used except in the following cases:

- Long span bounded edentulous areas.

- Weak posterior abutments that may be possibly removed and change the case into a
Kennedy class II

- Anterior edentulous spans requiring aesthetic that is provided by the colour of acrylic
resin.

- Patients susceptible to bone resorption that may require future relining e.g. diabetic
patient and after recent extractions.

2- Rests:

      Rests are usually placed on the near zone of the abutment teeth to provide
adequate support (fig. 6-4). Rest seats can be prepared in either a box-shaped or saucer
-shaped configuration depending on the condition of the abutment teeth.

3- Clasps:

      Rigid clasps are usually used on abutments bounding the edentulous area. An
embrasure clasp is used on the intact (dentulous) side.

4- Major connectors:

       A lingual bar is used for mandibular denture and a palatal bar or palatal strap is
used for maxillary denture.




                                                                            Mostafa Fayad 41
                                                               PARTIAL DENTURE DESIGN

Class III having modification areas:

       Modification of class III involving short saddle are common in upper jaw.
When the saddles are short and the abutment teeth are supported with sound healthy
bone, a number of small fixed bridges may be the treatment of choice. Also a
removable partial denture can be constructed.

        When a modification space is present, the same principles for designing a
bilateral denture are followed. However, four supporting rests should be used one on
each abutment bounding the edentulous areas.

        When Class III having long edentulous spans and modification spaces, they are
usually considered tooth tissue supported dentures. Maximum coverage of the residual
ridge and palatal tissues is required to provide adequate denture support retention of
the denture abutment from physical forces as adhesion in addition to wrought wire
clasps.

       When the condition of upper teeth is not good, the best result can be obtained
by using Every denture.

Every denture
Indication of Every denture:

      Indicated in class III with many modifications and when the condition of the
abutment is not good.

Principles of Every's partial denture design

1- Point contact between the abutment and artificial teeth:

        By making. contact point, not contact area, the lateral forces are distributed
mesiodistally along many teeth in the arch. Porcelain teeth is preferable to reduce wear
in this cases. The lateral forces in Every denture are resisted by the palate, the buccal
mucosa and anterior abutment teeth if present.

2- Wide embrasures between abutment and artificial teeth:

To allow natural stimulation of the gingiva and cleaning of the teeth .

3- Uncovered gingival

To prevent pockets between the denture and the tooth substance and allow natural
stimulation of the gingiva .

4- Contact of the denture with a stabilizer (round Wire) distal surface of the last
standing tooth:


                                                                           Mostafa Fayad 42
                                                                         PARTIAL DENTURE DESIGN

This stabilizer (round Wire) is used to prevent distal drifting of this tooth.

5- Maximum retention following the principles used in complete denture
construction:

- Maximum coverage of the palate and full extension of the flanges.

- Peripheral darning antroposterior.

- Proper shaping of the polished surface to allow better muscular control.

- Free sliding occlusion: To reduce denture displacement during lateral movement.

- Free occlusion: Is a type of occlusion which permits the mandible to slide from one
position to another, with the upper and lower teeth in contact and without
intercuspation.

N.B. The base material will be acrylic resin with straight round wire used to form the
stabilizer positioned posterior to the last standing tooth on each side of the arch.

        Cobalt Chromium base may be used to overcome the disadvantages of acrylic
resin (lack of strength).



                            Essentials of Design for Class III
I- Direct retention

1.Retention  can be achieved with much less potential harmful effect on the abutment teeth than
  with the class I or II arch.

2.The position of the retentive undercut on abutment teeth is not critical.

2- Clasps :

1.The quadrilateral positioning of direct retainers is ideal.

2.The type of clasp selected is not critical.

            Tooth and tissue contours and esthetics should be considered, and the simplest clasp
      possible selected.

            If restorations are required to correct tooth contours, the wax patterns must be shaped
      with the surveyor.

             Bracing arms must be rigid.

3- Rests

1.Rest seats should be prepared next to the edentulous space when possible.



                                                                                   Mostafa Fayad 43
                                                                            PARTIAL DENTURE DESIGN

2.Rests should be used to support the major connector and lingual plating.

4- Indirect retention

1.Indirect retention is usually not required.

2.If one or both of the posterior abutment teeth are used for vertical support alone without retentive
  clasp arms, the entire design must follow the requirements of a class I or II design.

5- Major and minor connectors

- They must be rigid and meet the same requirements as for a class ! or II design.

6- Occlusion

- The requirements for occlusion are same as for a class I or II design.



7- Denture base

1.A functional type impression is not required.

2.The extent of coverage of the residual ridge areas should be determined by appearance, comfort,
  and the avoidance of food impaction areas.

Differentiation between two main types of removable partial dentures

                                    Distal extension bases                 Bounded short saddle
Manner of support                   derive their primary support from      derives all of its support from
                                    the tissue underlying the base         the abutment teeth
                                    and secondary support
                                    from the abutment teeth
Method        of      impression
registration
Need for indirect retention
Base material                     Necessitates the use of a base           Metal bases are more
                                  material that can be relined to          frequently used
                                  compensate for tissue changes.
requirements       for     direct - clasp used in conjunction with a       - Cast retentive arms are
retention                         mesial rest, wrought-wire or bar-        generally used
                                  type retentive arm, combination          - Only requirement of such
                                  clasp                                    clasps is that they flex
                                  - must be able to flex sufficiently      sufficiently
                                  to dissipate stresses that               during placement and removal
                                  otherwise would be transmitted           of the denture to pass over the
                                  directly to the abutment tooth as        height of contour of the teeth in
                                  leverage.                                approaching or escaping from
                                                                           an undercut area.




                                                                                          Mostafa Fayad 44
                                                               PARTIAL DENTURE DESIGN




                             Kennedy Class IV
                                                                                           !!
        Kennedy class IV partial dentures are constructed to restore anterior edentulous
spans that cross the midline. Long class IV cases are designed following the principles
of free end saddle cases because the edentulous area exhibits abutments that lie
posterior to the edentulous area and lacks anterior abutments.

Problems associated with class IV cases
  1-Class IV cases are tooth-tissue supported; they are supported anteriorly by the
    tissues and posteriorly by the abutment teeth. Thus they exhibit problems
    associated with free end saddles. Lack of adequate support and retention causes
    rotation of the partial denture around the abutment resulting in torque effect on
    abutment teeth. The amount of torque is affected by:

     - The degree of resiliency of the mucosa covering the residual ridge.

     - Form of the dental arch; In V-shaped arches the artificial anterior teeth will be
     more distant from the fulcrum axis, thus, the magnitude of displacing forces will
     be more leading to excessive torque on abutment teeth.

  2- Class IV cases occur at any age but are usually predominant in children and
     adolescents because anterior teeth especially upper teeth are subjected to trauma.


                                                                           Mostafa Fayad 45
                                                               PARTIAL DENTURE DESIGN

  3- The need for an esthetic restoration is a pre-requisite due to the anterior location
     of the edentulous area.

  4- Frequent follow-up is usually required to detect the need for relining to
     compensate for ridge resorption.

Restoration of class IV cases
      Missing anterior teeth are preferably restored with fixed partial dentures,
implant supported removable or fixed partial dentures, or cast metal partial dentures
depending on the condition and length of the edentulous area and the condition of
abutment teeth.




I- Temporary restorations for class IV cases
II- Skeleton designs for class IV cases (metal RPDs)
     A- Skeleton design (metal RPDs) for short anterior spans
         The first Design uses an anterior clasping system.
         The second design uses a posteriorly placed clasping system
     B- Skeleton design (metal RPDs) for long anterior spans



                                                                          Mostafa Fayad 46
                                                                 PARTIAL DENTURE DESIGN

I- Temporary restorations for class IV cases
Temporary acrylic partial dentures may sometimes be required as in the following
cases;

-In children where:

     *Roots of abutment teeth are still incompletely formed.

     *Bone growth is not yet completed.

     *Space maintainer is required.

     *Danger of further trauma is still expected.

-In adults where:

     *Extensive mouth preparation is required.

     *Bone remodeling is anticipated after recent extraction of teeth.

      The most commonly used temporary appliance for restoring anterior teeth is the
Spoon denture. It can be constructed for both children and adults.



Spoon Dentures

          - The spoon denture is a tissue supported denture

          - usually constructed in acrylic resin but may sometimes be made in cast
            metal.

          - The spoon denture usually covers a large area of the palate to attain
            adequate support and to overcome the problem of retention usually
            associated with temporary appliances.

          - The lateral borders of the denture are usually placed 3-4mm away from the
            gingival margin to avoid caries and gingivitis especially in children where
            adequate oral hygiene measures cannot be fulfilled.

          - It is usually extended to the junction of hard and soft palate in order to:

                  -Gain retention through physical means as adhesion, cohesion and
                   interfacial surface tension.

                  -Obtain posterior palatal seal required to enhance retention.




                                                                             Mostafa Fayad 47
                                                               PARTIAL DENTURE DESIGN

Spoon dentures could be modified to enhance retention by:

   - Extending the posterior part of the palatal plate laterally above the survey line of
   the first permanent molars. The first molar is then clasped by a 7mm stainless steel
   wire in the form of an Adam's crib. This design may be used where it is possible
   to adapte thin wire between opposing arches without interfering with occlusion.

   - production of a cast cobalt chromium base with clasps engaging the buccal
   undercuts of the molar teeth (T-shaped cobalt chromium denture).

   - Construction of a combined metal acrylic palatal portion. The anterior part is
   made in the form of cast chromium cobalt base joined to an acrylic resin posterior
   extension carrying an Adam's clasp on the first molar.

The success of spoon denture depends on:

   o The nature of the mucosa: best retention is obtained from firm mucosa of
     adequate thickness rather than thin mucosa.

   o Form of the hard palate: Large palate having moderate slopes provides better
     retention by adhesion and cohesion and good stability. Flat palate provides
     better retention and less stability compared to palates exhibiting steep slopes
     where better stability and less retention are anticipated.

   o Presence of an anterior labial flange to counteract displacement of the posterior
     part of the restoration.

   o The degree of overlap of anterior teeth; the presence of deep overlap usually
     associated with partial loss of teeth especially in adults induces excessive
     stresses on the partial denture.

   o The closeness of the occlusion: metal backings may have to be provided as an
     integral part of the casting.

   o Incising food by the anterior denture teeth should be avoided to prevent
      displacement of the denture.

Advantages:

           • Small technical and chairside time.
           • Gingivitis and caries are not caused (the gingival margins are left
           uncovered and no extensive contact is made with the standing teeth)
Disadvantage:
           • Poor retention.
           • Displaced during incision so It is advisable to use radio opaque resin .
                                                                          Mostafa Fayad 48
                                                                PARTIAL DENTURE DESIGN

II- Skeleton designs for class IV cases (metal RPDs)
         Removable partial dentures are alternatives to fixed bridges in the following
cases:

           Cases where marked bone resorption necessitates the addition of an
            anterior labial flange to restore esthetics and provide lip support.

           Cases having long, markedly curved edentulous spans as this may add
            excessive stresses to abutments.

           Patients who refuse extensive preparations required to prepare abutments
            for fixed bridges.

A- Skeleton design (metal RPDs) for short anterior spans
         Two skeleton designs are proposed for short span class IV cases:

         1-The first Design uses an anterior clasping system.

        Retainers in the form of attachments or bar clasps are placed on the canines or
the first premolars. However, this places excessive stresses on the canines. For this
reason," the canines should be diagnosed with long well formed roots to resist torque.

      In this case, the denture is designed with a combined denture base, rests on the
neighboring natural teeth for support, bar clasps as retainers, preferably on first
premolars, and an anterior palatal strap as the major connector.

       Anterior retention may gained by using mesio-distal clasping on canine and
may reinforce by using Aker on first premolar. M. Connector: U-Shaped horse shoe.
Indirect R. : distal O-Rest on 4.

       It is indicated only when 1\ 1 are only missed and perfect bone support for
canines. Contra-indicated in cases where torque is marked as in excessive bone
resorption or more than 2 teeth are missing.

         2-The second design uses a posteriorly placed clasping system.

       The clasps are placed as far posteriorly as possible. This system is more
favorable because it provides better retention and indirect retention. It is also
esthetically more satisfactory. Canines are also protected from torque that may be
implied by clasping.

       In this case, the denture is designed with a combined denture base, rests on the
neighboring natural teeth usually canines for support and an Aker clasp (embrasure
clasp) or multiple Aker clasp placed on the two last standing molars on each side of
the dental arch.

                                                                            Mostafa Fayad 49
                                                                PARTIAL DENTURE DESIGN

      Support: rests on canines & posterior abutments or tooth supported posteriorly
 & tissue supported anteriorly.

      Retention: Double or Multiple Aker posteriorly and anterior flange engaging
 tissue undercut.

      Major connector: two palatal bar connectors arising from the saddle and placed
 on the lateral walls of the palate equi-distance between the gingival margins and the
 midline. The distal ends of the bars are attached to the posteriorly placed double Aker
 clasps on both sides.

      Indirect retention is encountered by the rests of the posterior clasps

       3- An alternative form of treatment when the saddle is short is the sectional
denture in cases of large proximal undercuts on the natural anterior teeth.

       One section is cast in metal and is inserted from the palatal aspect of the ridge,
which enables the proximal undercuts of the abutment teeth to be engaged. The labial
section which carries the teeth and the labial flange is inserted from below in an
upwards and backwards path. It is frictionally retained to the first section by means of
split post matrices attached to the cast portion, which will engage a stainless steel tube
matrix in the labial section.

       A design can also be used which incorporates a hinge between the two parts,
with the anterior flange and teeth being rotated into place and held in position by a
locking bolt. Retention may be improved by use of intracoronal attachments for the
first section.




                                                                            Mostafa Fayad 50
                                                                 PARTIAL DENTURE DESIGN

Composite Bonded Bridges

        When the permanent replacement of a single lost anterior tooth by a
removable partial denture is not entirely satisfactory and fixed bridge is rejected most
of these objections can be overcome by the use of an etched cast ceramometal
restoration which can be bonded to minimally prepared and etched enamel surfaces.

        Retention of the framework was improved by subjecting its fitting surface to an

electrolytic etching process. This improved the resin bond by establishing mechanical
retention between the micropores of the etched alloy surface and the composite resin
in a manner similar to its attachment to an etched enamel surface.

        Teeth with inadequate support, large carious lesions, extensive restorations, and
evidence of severe attrition are not suitable for use as abutments.

        Tooth preparation for this prosthesis should be minimal. Enamel may be
reduced to free the occlusal if necessary, but it must be stressed that it is preferable
that the attachment is placed on a non-functional surface. This will reduce the
possibility of mechanical displacement. A definitive path of insertion should be
created which should be vertical with small grooves or slots prepared on the proximal
surfaces of the abutment teeth Defining a cingulum rest area will also provide
additional vertical support. The whole area of the preparation should be kept clear of
the gingival margin by at least 1 mm. At insertion the tooth surface is prepared in the
normal manner for an acid etched restoration. A bonding agent is used on the enamel
and the luting composite applied to the casting.

        The advantages of this technique are that a saddle of limited span can be
restored economically without loss of healthy tooth substance or the wearing of a large
partial denture. For aesthetic reasons it is not suitable where there is obvious soft tissue
loss.




                                                                             Mostafa Fayad 51
                                                                 PARTIAL DENTURE DESIGN

B- Skeleton design (metal RPDs) for long anterior spans

       Long anterior edentulous areas which may extend to include premolars usually
occur in adults. Hence, a permanent restoration in the form of metal partial dentures is
the treatment of choice.

- Denture base: The denture is tooth-tissue supported; therefore a combination metal-
acrylic base is required. In upper class IV dentures the whole of the anterior part of the
hard palate can be covered to provide adequate denture support, resist sinking of the
denture and to increase retention by adhesion.

- Multiple clasping is required to help in splinting of the remaining teeth and in order
to widely distribute the stresses and torque action. Since the remaining naturally teeth
are usually posterior teeth. Therefore the clasping system is usually better than in long
class I cases having anterior teeth as abutments.

- Indirect retention is obtained by extending the palatal plate major connector
posterior to the fulcrum axis and through the rests of the posteriorly located clasps.

- Stress breakers may not be necessarily used in upper class IV cases due to the
good support obtained from palatal coverage. However, a stress broken design may be
required if a long edentulous area covered by compressible tissues is to be restored.

- As with free end saddles frequent inspection and rebasing are necessary since only a
slight degree of rotation about the occlusal rests will open up a space between the
posterior periphery of the denture base and the hard palate, into which food will find
its way.

Class IV in lower denture

       Usually required in adults who have lost the four lower anterior teeth through
periodontal disease or rarely caries. In this situation a cast metal denture is the
treatment of choice.

       The design consists of bilateral lingual bars extending posteriorly from the
saddle, terminating in clasps; continuous clasping may or may not be present. The
saddle must be adequately tooth supported anteriorly, and this can be accomplished by


                                                                             Mostafa Fayad 52
                                                                PARTIAL DENTURE DESIGN

using rests on the mesial aspect of the occlusal surfaces of the premolars. The use
of the canines for support has the advantage of bringing the axis of rotation forward so
that the posterior clasping is consequently more effectively but will necessitate
extensive preparation of the teeth to provide effective seats for the rests on the cingula
or else the use of incisal edge rests with their obvious aesthetic disadvantages.

                         Essentials of Design for Class IV
1.The movements of this type of removable partial denture and the resulting stresses
 transmitted to the abutment teeth are unlike the pattern seen in any other type of
 prosthesis.

2.The esthetic arrangement of the anterior replacement teeth may necessitate their
 placement anterior to the crest of the residual ridge, resulting in potential tilting
 leverage.

Every effort should be made to minimize these stresses. Some possibilities follow:

1.As   much of the labial alveolar process should be preserved as possible.

2.A central incisor or other tooth should be retained to serve as an intermediate
 abutment or as an overdenture abutment.

3.A critical evaluation of each remaining tooth in the arch should be made with the
 intent of retaining as many teeth as possible.

             The shorter the edentulous area, the less will be the harmful tilting
           leverage.

             Strategic clasp position should be used. The quadrilateral configuration,
           with the anterior clasps placed as far anterior and the posterior clasps placed
           as far posterior as possible, would be the ideal.

            The major connector should be rigid, and broad palatal coverage should be
           used in the maxillary arch.

            Indirect retention should be used as far posterior to the fulcrum line as
           possible.

           -  An ideal quadrilateral configuration of clasping may preclude the need for
           an additional indirect retainer.

           -  A functional type of impression may be indicated if the edentulous area is
           extensive.



                                                                              Mostafa Fayad 53
                                                                Mouth preparation


                 PREPARATION OF MOUTH FOR
               REMOVABLE PARTIAL DENTURES


        Mouth preparation follows the preliminary diagnosis and the
development of a tentative treatment plan. Final treatment planning may be
deferred until the response to the preparatory procedures can be ascertained.

In general, mouth preparation includes procedures in four categories:

      Relief of Pain and Infection
      oral surgical preparation,
      conditioning of abused and irritated tissue,
      periodontal preparation,
      preparation of abutment teeth.


Relief of Pain and Infection:
        Dental conditions that are causing discomfort should be treated as soon
        as possible such as necessary endodontic treatment or restorative filling
        for carious teeth. Gingival tissues should be treated to prevent
        exacerbation of inflammatory response. Also scaling, root planning, and
        prophylaxis should be performed.

A] RESTORATIVE PREPARATION

A.      Removal of caries.

B.      Replacement of defective restorations.

C.      Restoration of structurally compromised teeth.

D.      Occlusal modification.

E.      Correction of malocclusion.

F.      Splinting of natural teeth.



                                                                  Mostafa Fayad 1
                                                                 Mouth preparation


G.      Correction of unacceptable abutment tooth contours not cor¬rectable
        through enamel modification.

H.      Exposure of dentin during abutment tooth modification.

           1.   Sensitivity.

           2.   Caries susceptibility.



B] ENDODONTIC

A.      Non-vital teeth. Non-vital teeth should be endodontically treated.

B.      Endodontically treated abutment teeth.

            1. Placement of conservative intraradicular posts with minimal
            removal of tooth structure may increase resistance to structural
            failure.

            2. May require restoration with extracoronal cast restorations to
            resist structural failure.

C] ORTHODONTIC

A. Abutment teeth.

      1.        Axial inclination may require correction.

      2.        Infraeruption or supraeruption requiring correction.

B. Occlusal plane. Irregularities may be corrected by orthodontic therapy.

C. Edentulous spans. Asymmetrical or undersized edentulous areas which are
      not conducive to the artificial replacement of missing teeth may require
      modification.




D]ORAL SURGICAL PREPARATION:

     Oral surgical and periodontal procedures should precede abutment tooth
preparation and should be completed far enough in advance to allow the
necessary healing period. If at all possible, at least 6 weeks, but preferably 3 to


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                                                                  Mouth preparation


6 months, should be provided between surgical and restorative dentistry
procedures.



       Extractions:

       Regardless of its condition, each tooth must be evaluated concerning its
       strategic importance and its potential contribution to the success of the
       removable partial denture.

       Removal of Residual Roots

   All retained roots or root fragments should be removed. This is particularly
true if they are in close proximity to the tissue surface or if there is evidence of
associated pathological findings. Residual roots adjacent to abutment teeth may
contribute to the progression of periodontal pockets and compromise the results
from subsequent periodontal therapy.

       Impacted Teeth

   All impacted teeth, including those in edentulous areas and those adjacent
to abutment teeth, should be considered for removal. If an impacted tooth is
left, it should be recorded in the patient's record and the patient should be
informed of its presence. Roentgenograms should be taken at reasonable
intervals to be sure that no adverse changes occur.

Any impacted teeth that can be reached with a periodontal probe must be
removed to treat the periodontal pocket and prevent more extensive damage

       Malposed Teeth

   Individual teeth or groups of teeth and their supporting alveolar bone can be
surgically repositioned. Orthodontics may be useful in correcting many
occlusal discrepancies, but for some patients, such treatment may not be




                                                                    Mostafa Fayad 3
                                                               Mouth preparation


practical because of a lack of teeth for anchoring orthodontic appliances or for
other reasons.

          Cysts and Odontogenic Tumors

   The patient should be informed of the diagnosis and provided with various
options for resolution of the abnormality as confirmed by the pathologist's
report.

          Exostoses and Tori

   Modification of denture design can accommodate for exostoses, this may
results in additional stress to the supporting elements and compromised
function.

   The removal of exostoses and tori is not a complex procedure, and the
advantages from removal are great in contrast to the deleterious effects their
continued presence can create.

          Hyperplastic Tissue

   Hyperplastic tissue is seen in the form of fibrous tuberosities, soft flabby
ridges, folds of redundant tissue in the vestibule or floor of the mouth, and
palatal papillomatosis.

   All these forms of excess tissue should be removed to provide a firm base
for the denture. This removal will produce a more stable denture, reduce stress
and strain on the supporting teeth and tissue, and in many instances will
provide a more favorable orientation of the occlusal plane and arch form for the
arrangement of the artificial teeth.

          Muscle Attachments and Frena

   The maxillary labial and mandibular lingual frena are the most common
sources of frenum interference with denture design. These can be modified
easily with any of several surgical procedures. Under no circumstances should


                                                                 Mostafa Fayad 4
                                                                Mouth preparation


a frenum be allowed to compromise the design or comfort of a removable
partial denture.

       Bony Spines and Knife-Edge Ridges

   Sharp bony spicules should be removed and knifelike crests gently rounded.
If, the correction of (a knife-edge) residual crest results in insufficient ridge
support for the denture base, the dentist should resort to vestibular deepening
for correction of the deficiency or insertion of the various bone grafting
materials that have demonstrated successful clinical trials.

       Polyps, Papillomas, and Traumatic Hemangiomas

All abnormal soft tissue lesions should be excised and submitted for
pathological examination before the fabrication of a removable partial denture.

       Hyperkeratoses, Erythroplasia, and Ulcerations

All abnormal, white, red, or ulcerative lesions should be investigated regardless
of their relationship to the proposed denture base or framework. A biopsy of
areas larger than 5 mm should be completed, and if the lesions are large (more
than 2 cm in diameter), multiple biopsies should be taken.

       Dentofacial Deformity

Patients with a dentofacial deformity often have multiple missing teeth as part
of their problem. Correction of the jaw deformity can simplify the dental
rehabilitation.

       Osseointegrated Devices

A number of implant devices to support the replacement of teeth have been
introduced to the dental profession. These devices offer a significant stabilizing
effect on dental prostheses through a rigid connection to living bone.

       Augmentation of Alveolar Bone



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                                                                Mouth preparation


    Considerable attention has been devoted to ridge augmentation with the use
of autogenous and alloplastic materials, especially in preparation for implant
placement.

E] CONDITIONING OF ABUSED AND IRRITATED TISSUE

        Patients who require conditioning treatment often demonstrate the
following symptoms:

1. Inflammation and irritation of the mucosa covering the denture bearing areas

2. Distortion of normal anatomic structures, such as incisive papillae, the rugae,
and the retromolar pads

3. A burning sensation in residual ridge areas, the tongue, and the cheeks and
lips.

        These conditions are usually associated with ill fitting or poorly
occluding removable partial dentures. However, nutritional deficiencies,
endocrine imbalances, severe health problems (diabetes or blood dyscrasias),
and bruxism must be considered in a differential diagnosis.

        The first treatment procedure should be an immediate institution of a
good home care program.

     A suggested home care program includes rinsing the mouth three times
        a day with a prescribed saline solution;

     massaging the residual ridge areas, palate,and tongue with a soft
        toothbrush;

     removing the prosthesis at night;

     using a prescribed therapeutic multiple vitamin

     Prescribed high-protein, low-carbohydrate diet.

     Removing the ill-fitting dentures for extended periods.


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                                                              Mouth preparation


 Use of Tissue Conditioning Materials

          These soft materials apparently have a massaging effect on
   irritated mucosa, and because they are soft, occlusal forces are probably
   more evenly distributed.

          Maximum benefit from using tissue conditioning materials may
   be obtained by

   (1) Eliminating deflective or interfering occlusal contacts of old
   dentures (by remounting in an articulator if necessary);

   (2) Extending denture bases to proper form to enhance support,
   retention, and stability

   (3) Relieving the tissue side of denture bases sufficiently (2 mm) to
   provide space for even thickness and distribution of conditioning
   material;

   (4) applying the material in amounts sufficient to provide support and a
   cushioning effect

   (5) following the manufacturer's directions for manipulation and
   placement of the conditioning material.




          Many dentists find that intervals of 4 to 7 days between changes
   of the conditioning material are clinically acceptable. If positive results
   are not seen within 3 to 4 weeks, one should suspect more serious health
   problems and request a consultation from a physician.




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                                                                Mouth preparation




F] PERIODONTAL PREPARATION

       The periodontal health of the remaining teeth, especially those to be
used as abutments, must be evaluated carefully by the dentist and corrective
measures instituted before removable partial denture fabrication.

       It is strongly recommended that a gross debridement be performed
before tooth extraction when patients have significant calculus accumulation.
This helps limit the possibility of accidentally dislodging a piece of calculus
into the extraction socket, which could lead to an infection.

       Objectives of Periodontal Therapy

    1. Removal and control of all etiological factors contributing to
     periodontal disease, along with a reduction or elimination of bleeding on
     probing

    2. Elimination of, reduction in, pocket depths of all pockets.

    3. Establishment of functional atraumatic occlusal relationships and tooth
     stability

    4. Development of a personal plaque control program and definitive
     maintenance schedule.

       Periodontal Diagnosis and Treatment Planning

       evaluation procedure :

       1) Exploration of the gingival sulcus and

       2) Recording of the probing pocket depth

       3) Sites that bleed on probing with a suitably designed periodontal
 probe.




                                                                    Mostafa Fayad 8
                                                                Mouth preparation


       4) Dental radiographs can be used to supplement the clinical
examination but should not be used as a substitute for it.

       A critical evaluation of the following factors should be made:

       (1) Type, location, and severity of bone loss;

       (2) Location, severity, and distribution of furcation involvements;

       (3) Alterations of the periodontal ligament space;

       (4) Alterations of the lamina dura;

       (5) Presence of calcified deposits;

       (6) Location and conformity of restorative margins;

       (7) Evaluation of crown and root morphologies;

       (8) Root proximity;

       (9) Caries;

       (10) Evaluation of other associated anatomic features, such as the
mandibular canal or sinus proximity.

       Treatment Planning

       Periodontal treatment planning can

       Usually be divided into three phases.

           The first phase is considered disease control or initial therapy
              which include oral hygiene instruction, scaling, and root planning
              and polishing along with endodontic, occlusal adjustment, and
              temporary splinting,

           In the second—or periodontal—surgical phase, any needed
              periodontal surgery is accomplished, including free gingival
              grafts, osseous grafts, or pocket reduction.

                                                                  Mostafa Fayad 9
                                                                  Mouth preparation


             maintenance of periodontal health (definitive recall) phase ; A
               definitive recall schedule should be established with the patient
               and is usually kept at 3- to 4- month intervals.

       Tooth mobility

       Each tooth should be evaluated carefully for mobility. Normal mobility
is in the order of 0. 05 to 0. 10 mm.

       Primary mobility caused by; inflammatory changes in the periodontal
ligament, traumatic occlusion, loss of attachment, or a combination of the three
factors. Mobility due to occlusal interference may disappear after selective
grinding.

       Secondary mobility resulting from the presence of an inflammatory
lesion may be reversible if the disease process has not destroyed too much of
the attachment apparatus.

             Grade I mobility is present when there is less than 1 mm of
               movement in a buccolingual direction;

             grade II is present when mobility in the buccolingual direction is
               between 1 to 2 mm,

             grade III is present when there is greater than 2 mm of mobility
               in the buccolingual direction and/or the tooth is vertically
               depressible.

            Management

            Teeth may be immobilized during periodontal treatment by acid
            etching teeth with composite resin, with fiber reinforced resins, with
            cast removable splints, or with intracoronal attachments.

            After periodontal treatment, splinting may be accomplished with
            cast removable restorations or      cast cemented restorations. The


                                                                   Mostafa Fayad 10
                                                        Mouth preparation


   preferred form of permanent splinting is with two or more cast
   restorations soldered or cast together. They may be cemented with
   either permanent (zinc oxyphosphate or resin) cements or temporary
   (zinc oxide-eugenol) cements. A properly designed removable partial
   denture can also stabilize mobile teeth if provision for such
   immobilization is planned as the denture is designed.

       The night guard is a removable acrylic resin splint, originally
   designed as an aid in eliminating the deleterious effect of nocturnal
   clenching and grinding. It may be helpful as a form of temporary
   splinting if worn at night after the removal of the removable partial
   denture. The flat occlusal surface prevents the intercuspation of the
   teeth, which eliminates lateral occlusal forces

Elimination of Cross Occlusal Interferences

       Traumatic cuspal interferences are removed by a selective
grinding procedure. An attempt is made to establish a positive planned
intercuspal position that coincides with centric relation. Deflective
contacts in the centric path of closure are removed,

       The presence of working and nonworking interferences should be
evaluated, and if present, they should be removed.

       The indication for occlusal adjustment is based on the presence of
a pathological condition rather than on a preconceived articulation
pattern.

Guide to Occlusal Adjustment:

       In evaluation of occlusal disharmony of the natural dentition,
accurately mounted diagnostic casts are essential in determining static
cusp to fossa contacts of opposing teeth and as a guide in the correction
of occlusal anomalies in both centric and eccentric functional relations.
Ground tooth surfaces should be subsequently smoothed and polished.

                                                           Mostafa Fayad 11
                                                          Mouth preparation


       Schuyler has provided the following guide to occlusal adjustment
by selective grinding

I-Grinding In Centric Occlusion:

       A static coordinated occlusal contact of the maximum number
of teeth (maximum intercuspal position) when the mandible is in centric
relation to the maxilla should be the first objective.

       Articulating paper is used with an open and close movement of
the articulator or the mandible in intraoral method, to discover any
traumatic points on the occlusal surfaces of the teeth. These are removed
until even contact throughout the arch is obtained.

       In the posterior teeth the surfaces to be reduced are selected
according to two basic rules:

        a-    If the cusp is high in both centric and eccentric occlusion,
         reduce the cusp.

        b-    If the cusp is high in centric but not in eccentric occlusion,
         deepen the fossa.

       In anterior teeth:

       a- When anterior teeth are in premature contact in centric
relation, or in both centric and eccentric relations, corrections should be
made by grinding the incisal edges of the mandibular teeth.

       b- If premature contact occurs only in the eccentric relation,
correction must be made by grinding the lingual inclines of the
maxillary teeth.

       Premature contacts in centric relation are relieved by:

       - Grinding the buccal cusps of the mandibular teeth,

       - The lingual cusps of maxillary teeth,
                                                           Mostafa Fayad 12
                                                            Mouth preparation


       - The incisal edges of the mandibular anterior teeth.

       Deepening the fossa of a posterior tooth or the lingual contact
area in centric relation of a maxillary anterior tooth changes and
increases the steepness of the eccentric guiding inclines of the tooth.
Although this relieves trauma in centric relation, it may predispose the
tooth to trauma in eccentric relations.

II-Grinding To Obtain Occlusal Balance in Lateral Movements:

A- Anterior teeth:

       If the anterior dentition is found to be in traumatic contact reduce
the traumatic areas of contact using the following rules:

          a- Reduce the lingual surfaces of the maxillary incisal edges.

          b- Reduce the labial surfaces of the mandibular incisal edges.

          c- Reduce the disto-lingual slopes of the maxillary cuspids
            (canines).

          d- Reduce the mesio-labial slopes of the mandibular cuspids.

B- Posterior teeth:

       Where the posterior dentition is found to be in traumatic contact
reduce the traumatic area of contact. The attention is directed first to
balancing side contacts. Using the following rules:

       1- Care must be exercised to prevent the loss of a static
supporting contact in centric relation. This static support in centric
relation may exist between the mandibular buccal cusp fitting into the
central fossa of the maxillary tooth or between the maxillary lingual
cusp fitting into the central fossa of the mandibular tooth or it may exist
in both situations.



                                                             Mostafa Fayad 13
                                                            Mouth preparation


         2- The mandibular buccal cusp is in a static central contact in the
maxillary sulcus more often than the maxillary lingual cusp is in a static
contact in its opposing mandibular sulcus. Therefore corrective
grinding to relieve premature balancing contacts is more often done
on the maxillary lingual cusps.

         Evidence of excessive balancing contacts:

         It is extremely difficult to differentiate the harmless from the
destructive because we cannot visualize the influence of these fulcrum
contacts on the functional movements of the condyle in the articular
fossa.

         - Subluxation,

         - Pain,

         - Lack of normal functional movement of the joint,

         - Loss of alveolar support of the teeth involved

         may be evidence of excessive balancing contacts. Balancing-side
contacts receive less frictional wear than working-side contacts, and
premature contacts may develop progressively with wear.

Balancing side:

         Corrective grinding to relieve premature balancing contacts is
more often done on the maxillary lingual cusps.

         In complete denture reduce the inner inclines of the
mandibular buccal cusps in preference to the opposing maxillary
slope. This is important because grinding usually involves removal in
part or whole of the cusp, which is an established centric occlusal
contact. Therefore the maxillary cusp is left to provide a more
stabilizing effect for the lower denture.


                                                             Mostafa Fayad 14
                                                          Mouth preparation




Working side:

       Anterior teeth: necessary grinding must be done on the lingual
       surfaces of the maxillary anterior teeth.

       posterior teeth: done on the buccal maxillary cusp of premolars
       and molars and on the lingual mandibular cusp of the premolars
       and molars.

Grind on 'bull' rule, to avoid the supporting cusps (the upper palatal
and the lower buccal cusps) which preserve the vertical dimension of
occlusion

    1- Reduce the inner inclines of maxillary buccal cusps.

    2- Reduce inner inclines of mandibular lingual cusps.

       Grinding of mandibular buccal cusps or maxillary lingual cusps
at this time would rob these cusps of their static contact in the opposing
central sulci in centric relation.




III-Grinding to Obtain Occlusal Balance in Protrusive Movements:

    1- If the anterior dentition is found to be in traumatic contact
    reduce the traumatic areas of contact by grinding the lingual surface
    of the maxillary anterior teeth.

       Anterior teeth should never be ground to bring the posterior teeth
    into contact in either protrusive position or on the balancing side.

    2- If the posterior dentition is found to be in traumatic contact
    reduce the traumatic areas of contact, grinding in accordance with
    the


                                                           Mostafa Fayad 15
                                                               Mouth preparation


      BULL Rule: Grind only cuspal slopes, which are not providing centric
      contact. Grind distal inclines of maxillary buccal cusps and mesial
      inclines of mandibular lingual cusps.

      3- Any sharp edges left by grinding should be rounded off.




G] Preparation of abutment teeth:
CLASSIFICATION OF ABUTMENT TEETH

The subject of abutment preparations may be grouped as follows:

    (1) those abutment teeth that require only minor modifications to their
     coronal portions, include :    teeth with sound enamel, those with small
     restorations not involved in the removable partialdenture design, those
     with acceptable restorations that will be involved in the removable partial
     denture design, and those that have existing crownrestorations requiring
     minor modification that will not jeopardize the integrity of the crown.

    (2) those that are to have restorations other than complete coverage crowns,

    (3) those that are to have crowns (complete coverage). they provide the best
     possible support for occlusal rests.

SEQUENCE OF ABUTMENT PREPARATIONS ON SOUND ENAMEL
OR EXISTING RESTORATIONS

Abutment preparations should be done in the following order:

1. Proximal surfaces parallel to the path of placement should be prepared to
provide guiding planes.

2. Tooth contours should be modified, lowering the height of contour so that




                                                                Mostafa Fayad 16
                                                               Mouth preparation


    (a) the origin of the circumferential clasp arms may be placed well below
     the occlusal surface, preferably at the junction of the middle and gingival
     thirds;

    (b) retentive clasp terminals may be placed in the gingival third of the
     crown for better esthetics and better mechanical advantage; and

    (c) reciprocal clasp arms may be placed on and above a height of contour
     that is no higher than the cervical portion of the middle third of the crown
     of the abutment tooth.

3. After alterations of axial contours are accomplished and before rest seat
preparations are instituted, an impression of the arch should be made in
irreversible hydrocolloid and a cast formed in a fast-setting stone. This cast
can be returned to the surveyor to determine the adequacy of axial alterations
before proceeding with rest seat preparations. If axial surfaces require
additional axial recontouring, it can be performed during the same appointment
and without compromise.

4. Occlusal rest areas should be prepared that will direct occlusal forces along
the long axis of the abutment tooth.

       Mouth preparation should follow the removable partial denture
design that was outlined on the diagnostic cast at the time the cast was
surveyed and the treatment plan confirmed. Proposed changes to abutment
teeth should be made on the diagnostic cast and outlined in colored pencil
to indicate the area, amount, and angulation of the modification to be done.




Preparation of the abutment teeth may be in the form of:



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                                                          Mouth preparation


     A. Reshaping of abutment teeth.

     B. Crowns.

     C. Rest seat preparation.




A- Reshaping of Abutment Teeth:

 1- Enameloplasty:

 Conservatism must be the rule when recontouring enamel surface.
 Enameloplasty may be performed for:

   a) Developing Guiding Planes:

       Guiding planes are surfaces on proximal or lingual surfaces of
 teeth that are parallel to each other and, more importantly, to the path of
 insertion and removal of a removable partial denture
 (RPD). There functions are:

    - On the proximal walls adjacent to edentulous
 spaces they provide parallism needed for ensuring
 stabilization.

    - Minimize wedging action between RPD and abutment.

    - Decrease undesirable space between RPD and the abutment tooth to
 increase retention by frictional resistance.

    - On the lingual surfaces of teeth provides maximum resistance to
 lateral stresses exerted by the retentive clasp arm during insertion and
 removal of RPD.

       Dimensions of the Guiding Plane:

       It is prepared by cylindrical diamond in the following dimensions:



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                                                                    Mouth preparation


      occlusogingivally it is 2-4 mm in length prepared flat on the occlusal
      third of the abutment.

      Buccolingually it is 3-4 mm in width and curved in harmony with the
      existing tooth contour.

         Ideal guiding plane is 2-4 mm occlusogingivally

       Normal tooth contour should be maintained

      b) Changing Height of Contour:

          The retentive clasp arm should be ideally located
      at the junction of the gingival and middle thirds not higher, for esthetic
      purpose and for definite mechanical advantage.

      But when, the height of contour lies near the occlusal surface in the
      tipped tooth this can be lowered by grinding
      (enameloplasty).

      1- High survey line may cause deformation of the clasp.

      2- Shaping the enamel to lowering the survey line.

C) Modification of Retentive Undercut:

            When there is insufficient under cut and when the patient has good
      oral hygiene and low caries index, these teeth can be modified by
      increasing amount of the undercut by contouring the
      enamel surface; By creation of gentle                depression
      (concavity) about 4mm in            mesiodistal length and
      0.01inch deep (not a pit or hole).

      This concavity is prepared by using a small, round end tapered diamond
      stone.




     B- crowns:

                                                                        Mostafa Fayad 19
                                                          Mouth preparation


    When the remaining teeth do not posses natural contours and the
enamel surfaces cannot be modified to create undercut, cast restoration
should be planed. Cast crown also may be planned in case of extensive
caries, defective restoration, tooth fracture, and endodontically treated
teeth.

         To shape the wax pattern of the crown, the wax knife is used to
carve the guiding plane on the surveyor.

         The pattern must be hand carved tom place the height of contour
in the middle third of lingual surface if the tooth is to receive a
reciprocal clasp arm and at the junction of the gingival and middle third
of the buccal surface to receive a retentive clasp arm.

The position and depth of the retentive undercut can be verified by use
of an undercut gauge.

Contouring Wax Patterns

         Modern indirect techniques permit the contouring of wax patterns
on the master cast with the aid of the surveyor blade. All abutment teeth
to be restored with castings can be prepared at one time and an
impression made that will provide an accurate stone replica of the
prepared arch. Wax patterns may then be refined on separated individual
dies or removable dies. All abutment surfaces facing edentulous areas
should be made parallel to the path of placement by the use of the
surveyor blade




C- Rest Seat Preparation:

The purposes and functions of rests basically, are to:

- Direct the forces of mastication parallel to the long axis of the
associated abutment.

                                                           Mostafa Fayad 20
                                                              Mouth preparation


    - Prevents the gingival displacement of a RPD.

    - Maintains the relationship between a clasp assembly and the
   associated tooth.

    - In certain applications a rest may act as an indirect retainer.

    - It may be used to close a small space between teeth, which restoring
   continuity of the arch and preventing food impaction.

   Each seat must be positioned in a properly prepared rest seat. These rest
   seats must be prepared before final impression and master cast are made.




         Rest Seat Preparation for Posterior Teeth:




   1) Occlusal Rest Seat in Enamel:

 The basically outline form of an occlusal rest seat is triangular, with its
   base directed at the marginal ridge and the apex toward the tooth center,
   occupying about one half of the buccolingual width of the occlusal
   surface, and the apex should be rounded as all margins of the
   preparation.

 An occlusal rest must be at least 1 mm thick at its thinnest point if
   chrome alloy is used for framework and about 1.5 mm if gold is to be
   used.

 Extension of the rest seat mesiodistally about one third to one half of the
   mesiodistal diameter.

 The floor of the occlusal rest seat must be inclined toward the center of
   the tooth to place the deepest part of the rest nearly at the center of the
   preparation.


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                                                             Mouth preparation


 The floor of the rest seat should be spoon in shape.

 Any sharp angle should be smoothed.

 An occlusal rest seat may be prepared using a variety of rotatory
   instruments. Many practitioners use round diamond burs, while others
   prefer diamond bur with rounded ends and tapering sides.

 When using round diamond bur care must be taken to avoid creation of
   mechanical undercut at the peripheries of the preparation.




   2) Occlusal Rest Seat as Part of a New Cast-metal Restoration:

          When one or more fixed restoration will be placed in conjunction
   with RPD, these restorations must be carefully planed and fabricated.
   Accordingly, occlusal rest seat for cast gold
   restorations should always be carved into
   the wax pattern following placement of
   guiding planes. (Figure 6)

   - A round carbide bur (No 4 or 6) is used to perform the initial shaping
   procedure for box-shaped rest

   - Upon completion of the casting process, the restoration is finished and
   polished using a small round fishing bur.

   3) Occlusal Rest Seat on the Surface of an Existing Cast-metal
   Restoration:

           Sometimes a RPD is indicated for a patient with one or more
   cast restorations on proposed partial denture abutments. Although it
   would be ideal to replace these restorations, the practitioner should try to
   contour these restorations to satisfy the requirements of the designed
   RPD.


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                                                          Mouth preparation


- When preparing rest seats in existing cast restoration, the
establishment of sufficient space should be the highest priority; so the
patient must be informed if perforation of this existing restoration
occurred that perforated restoration must be replaced.

- The instrumentation and procedures for preparing rest seats on existing
fixed restorations are identical to those for preparing rest seats on
enamel surfaces.




4) Occlusal Rest Seats on an Amalgam Restoration:

     A rest seat preparation on a multiple-surface amalgam restoration is
less desirable than a rest seat preparation on sound enamel or a cast
restoration.

- The amalgam alloy tends to deform when exposed to constant load.

- Care must be taken to avoid weaken the proximal portion of
the amalgam restoration at the ismuth during preparation.

- Experience indicates that rest seat should not be placed entirely
on amalgam. If a substantial portion of     the rest seat cannot be placed
on sound tooth structure, then a complete- or partial-coverage casting
should be considered.




  5) Embrasure Rest Seat:

      This preparation crosses the occlusal embrasure of two
approximating posterior teeth, from the mesial fossa of one tooth to the
distal fossa of the adjacent tooth; to receive an embrasure clasp.

- A diamond bur with a rounded end and

tapering sides is ideal for preparing embrasure rest seats.

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                                                            Mouth preparation


   - Contact between the teeth should not be broken since this may result in
   tooth migration or food impaction.




              Embrasure space dimensions

   - The form and depth of the rest seat: at the facial and lingual
   embrasures, the embrasure rest seat should be 3.0 to 3.5 mm wide and
   1.5 to 2.0 mm deep.

   - Occlusal clearance can be checked by laying two pieces of 18 gauge
   wires side by side across the preparation.

   - The patient should be able to close without contacting the metal.

   - The buccal inclines of the preparation must be rounded after the
   preparation is completed.

 Rest Seat Preparation for Anterior Teeth:

         In most cases an occlusal rest seat on a posterior tooth is preferred
   than a cingulum or incisal rest seat on an anterior teeth. Because of its
   size and position, this permits forces to be directed along the long axis
   of the teeth.

   1) Lingual or Cingulum Rest Seat:

 Indications:

   1- When there is no posterior tooth to place an occlusal rest.




                                                             Mostafa Fayad 24
                                                             Mouth preparation


  2- Maxillary canine is mainly used for lingual or cingulum rest, because
  the morphology of the tooth permits preparation of the seat.

  3- It is rarely used on incisors when the canine is missing. In this case
  multiple rests should be used to distribute the force over a number of
  incisors.

  4- To prepare rest seat in the enamel there should be (prominent
  cingulum, good oral hygiene, and low caries index).

 Design:

  1-the outline form of a cingulum rest seat should be crescent shaped
  when widowed from the lingual aspect. Its broadest portion is in the
  middle of the lingual surface and get less broad as it approaches the
  proximal surface.

  2- The rest seat should be V-shaped when viewed from the proximal;
  with rounded line angles. (This permits direction of the force along the
  long axis of the tooth).

  3- Mesiodistal length of preparation should be a minimum of 2.5 mm.
  labiolingual width about 2 mm, and incisal apical depth a minimum of
  1.5 mm.

  4- It is often difficult to obtain a positive epically inclined rest seat due
  to tooth angulations or anatomy. The use of cast restoration may be
  required to establish a definite rest seat.




 Preparation:

  a) Cingulum Rest Seat in Enamel:



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                                                             Mouth preparation


         A lingual or cingulum rest seat may be prepared in enamel if the
  tooth is sound, low caries index, good oral hygiene and prominent
  cingulum.

  A cingulum rest seat is accomplished using a carbide inverted
  cone bur (side- and end- cutting surfaces) in a high speed hand
  piece. The preparation is finished, polished, smoothen, and gently
  rounded using a rubber wheel in a low                  speed hand piece.

  b) Cingulum Rest Seat in Cast Restorations:

       The most satisfactory cingulum rest from the stand point of
  support is one that is placed on a prepared rest seat in a cast restoration.
  The rest seat should be carved in during the wax pattern stage, not cited
  or prepared in the cast restoration.




  2- Incisal Rest Seats in Enamel:

         Incisal rest seats are the least desirable rest seats for anterior
  teeth. Because of its bad esthetic, interference with occlusion, and its
  damaging effect on the abutment.

 Indications:

  1- Incisal rests are used mostly on mandibular canines when the
  abutment is sound and when a cast restoration is not indicated.

  2- It may be used as an auxiliary rest for indirect retention.

 Disadvantages:

  a) The bad esthetic of metal.

  b) Greater mechanical leverage than lingual rests, due to the longer
  minor connector required.


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                                                             Mouth preparation


 Design:

  1- An incisal rest seat is usually placed near a proximal surface, mostly
  on the proximal distal line angle of the tooth for esthetic.

  2- When viewed from the facial surface, its floor is concave in shape
  and inclined toward the center of the tooth to direct the force along to
  the long axis of the tooth.

  3- When viewed from the proximal, the outline form is convex (saddle
  shape) with buccal and lingual bevels.

  4- All borders are rounded and smooth.

  5- Its dimensions are approximately (2.5 mm wide and 1.5 mm deep).

 Preparation:

  An initial depth cut is made, using a tapered cylindrical stone, at the
  junction of the middle and the mesial or distal third
  of the abutment tooth.

  The walls of the rest seat are created by flaring the
  edges of the depth cut preparation and beveling the
  buccal and lingual walls with finishing bur. The
  completed preparation should be smooth and comfortable for the patient.




                       Special consideration


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                                                               Mouth preparation


Abutment preparations using conservative restorations

       When an inlay is the restoration of choice for an abutment tooth, certain
modifications of the outline form are necessary. To prevent the buccal and
lingual proximal margins from lying at or near the minor connector or the
occlusal rest, these margins must be extended well beyond the line angles of
the tooth. This additional extension may be accomplished by widening the
conventional box preparation.

       The restoration should be with maximum resistance and retention, and
with clinically imperceptible margins. The first requisite can be satisfied by
preparing opposing cavity walls 5° or less from parallel and producing flat
floors and sharp, clean line angles.

Abutment preparations using crowns

       One of the advantages of making cast restorations for abutment teeth is
that mouth preparations that would otherwise have to be done in the mouth
may be done on the surveyor with far greater accuracy. It is generally
impossible to make several proximal surfaces parallel to one another when
preparing them intraorally.

       The ideal crown restoration for a removable partial denture abutment is
the complete coverage crown, which can be carved, cast, and finished to ideally
satisfy all requirements for support, stabilization, and retention without
compromise for cosmetic reasons.

       The preparation should be made to
provide the appropriate depth for the occlusal
rest seat. This is best accomplished by altering
the axial contours of the tooth to the ideal
before preparing the tooth and creating a
depression in the prepared tooth at the
occlusal rest area.

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                                                                 Mouth preparation


Ledges on Abutment Crowns

       The functions of the reciprocal clasp arm are reciprocation,
stabilization, and auxiliary indirect retention. Any rigid reciprocal arm may
provide horizontal stabilization if it is located on axial surfaces parallel to the
path of placement.

       Its function as a reciprocating arm against the action of the retentive
clasp arm is limited only to stabilization against possible orthodontic
movement when the denture framework is in its terminal position. Such
reciprocation is needed when the retentive clasp produces an active orthodontic
force because of accidental distortion or improper design.

       The term orthodontic force is incorrect, because the term signifies a
slight but continuous influence that would logically reach equilibrium when the
tooth is orthodontically moved. Instead, the transient forces of placement and
removal are intermittent but forceful, which can lead to periodontal
destruction and eventual instability rather than to orthodontic movement.

       True reciprocation is not possible with a clasp arm that is placed on
an occlusally inclined tooth surface because it does not become effective
until the prosthesis is fully seated. When a dislodging force is applied, the
reciprocal clasp arm, along with the occlusal rest, breaks contact with the
supporting tooth surfaces, and they are no longer effective. Thus as the
retentive clasp flexes over the height of contour and exerts a horizontal force
on the abutment, reciprocation is nonexistent just when it is needed most.

       True reciprocation can be obtained only by creating a path of
placement for the reciprocal clasp arm that is parallel to other guiding
planes. In this manner the inferior border of the reciprocal clasp makes contact
with its guiding surface before the retentive clasp on the other side of the tooth
begins to flex.




                                                                  Mostafa Fayad 29
                                                                            Mouth preparation


        The presence of a ledge on the abutment crown acts as a terminal stop
for the reciprocal clasp arm. It also augments the occlusal rest and provides
indirect retention for a distal extension removable partial denture.

        A reciprocal clasp arm built on a crown ledge is actually inlayed into the
crown and reproduces more normal crown contours. The patient's tongue then
contacts a continuously convex surface rather than the projection of a clasp
arm.




   a; Open circle at top and bottom illustrates that retentive clasp is only passive at its first
contact with tooth during placement and when in its terminal position with denture fully
seated. During placement and removal, reciprocal rigid clasp arm placed on opposite side of
tooth cannot provide resistance against these horizontal forces.

  b. True reciprocation throughout full path of placement and removal is possible when
reciprocal clasp arm is inlaid onto ledge on abutment crown.




        The crown ledge may be used on any complete or three-quarter crown
restored surface that is opposite the retentive side of an abutment tooth. It is
used most frequently on premolars and molars but also may be used on canine
restorations. It is not ordinarily used on buccal surfaces for reciprocation
against lingual retention because of the excessive display of metal, but it may
be used just as effectively on posterior abutments when esthetics is not a factor.




                                                                             Mostafa Fayad 30
                                                                Mouth preparation


Spark Erosion

       Spark erosion technology is a highly advanced system for producing
the ultimate in precision fit of the reciprocal arm to the ledge on the
casting. This technology uses a tool system that permits repositioning the
casting with great accuracy and an electric discharge machine that is
programmed to erode minute metal particles through periodic spark intervals.

Veneered Crowns for Support of Clasp Arms

       Veneered crowns must be contoured to provide suitable retention.
This means that the veneer must be slightly overcontoured and then shaped to
provide the desired undercut for the location of the retentive clasp arm. If the
veneer is of porcelain, this procedure must precede glazing; if it is of resin, it
must precede final polishing.

       Porcelain laminates have demonstrated resistance to wear for the
equivalent of 5 years. The porcelain, however, resulted in slight wear on the
clasps. The flat underside of the cast clasp makes sufficient contact with the
surface of the veneer so that abrasion of the resin veneer may result.

       Present-day acrylic resins, being cross-linked copolymers, will
withstand abrasion for considerable time but not nearly to the same degree as
porcelain. Therefore acrylic resin veneers are best used in conjunction with
metal that supports the half-round clasp terminal.

SPLINTING OF ABUTMENT TEETH

       Splinting to the adjacent tooth or teeth can be used as a means of
improving abutment support. Thus two single-rooted teeth serve as a
multirooted abutment. Splinting should not be used to retain a tooth that would
otherwise be condemned for periodontal reasons.

       The most common application of the use of multiple abutments is the
splinting of two premolars or a first premolar and a canine. Mandibular


                                                                 Mostafa Fayad 31
                                                                Mouth preparation


premolars generally have round and tapered roots, which are easily loosened by
rotational and tipping forces. They are the weakest of the posterior abutments.

       Anterior teeth on which lingual rests are to
be placed often must be splinted together to
prevent orthodontic movement of individual teeth.
Mandibular anterior teeth are seldom used for
support, but if they are, splinting of the teeth
involved is advisable.

When splinting is impossible, individual lingual rests on cast restorations may
be slightly inclined apically to prevent possible tooth displacement, or lingual
rests may be used in conjunction with incisal rests, slightly engaging the labial
surface of the teeth.




USE OF ISOLATED TEETH AS ABUTMENTS

       The average abutment tooth is subjected to some distal tipping, rotation,
torquing, and horizontal movement, The isolated abutment tooth, however, is
subjected also to mesial tipping because of lack of proximal contact.

       In a tooth-supported prosthesis, an isolated tooth may be used as an
abutment by including a fifth abutment for additional support. Thus rotational
and horizontal forces are resisted by the additional stabilization obtained from
the fifth abutment. When two such isolated abutments exist, a sixth abutment
should be included for the same reason. Thus the two canines, the two isolated
premolars, and the two posterior teeth are used as abutments.

       An isolated anterior abutment adjacent to a distal extension base usually
should be splinted to the nearest tooth by means of a fixed partial denture. The
effect is twofold:




                                                                 Mostafa Fayad 32
                                                               Mouth preparation


           (1) The anterioredentulous segment is eliminated, thereby creating
            an intact dental arch anterior to the edentulous space; and

           (2) The isolated tooth is splinted to the other abutment of the fixed
            partial denture, thereby providing multiple abutment support.

Factors influence the decision to use an isolated tooth as an abutment:

1- Form, length of the root and the supporting bone

2- Esthetic consideration

MISSING ANTERIOR TEETH

       When a removable partial denture is to replace missing posterior teeth,
especially in the absence of distal abutments, any additional missing anterior
teeth are best replaced by means of fixed restorations rather than included in
the removable partial denture. In any distal extension situation, some
anteroposterior rotational action will result from the addition of an anterior
segment to the denture.

       It is generally advisable that a removable partial denture should replace
only the missing posterior teeth after the remainder of the anterior arch has
been made intact by fixed restorations.

       The decision to include an anterior segment on the denture depends
largely on the support available for that part of the removable partial denture.
The greater the number of natural anterior teeth remaining, the better the
available support for the edentulous segment.

       FABRICATING           RESTORATIONS TO                FIT     EXISTING
DENTURE RETAINERS

       The technique for making a crown to fit the inside of a clasp is as
follows:



                                                                  Mostafa Fayad 33
                                                               Mouth preparation


       1- An irreversible hydrocolloid impression of the mouth is made with
the removable partial denture in place.

       2- This impression, which is used to make the temporary crown, is
wrapped in a wet paper towel or placed in a plastic bag and set aside while the
tooth is being prepared.

       Even though several abutment teeth are to be restored, it is usually
necessary that each temporary restoration be completed before the next one is
begun. This is necessary so that the original support and occlusal relationship
of the removable partial denture can be maintained as each new temporary
crown is being made.

       3- During the preparation of the abutment tooth, the removable partial
denture is replaced frequently to ascertain that sufficient tooth structure is
removed to allow for the thickness of the casting.

       4- When the preparation is completed, an individual impression of the
tooth is obtained from which a stone die is made.

       5- A temporary crown is then made in the original irreversible
hydrocolloid impression. It is trimmed, polished, and temporarily cemented,
and the removable partial denture is returned to the mouth.

       6- The patient is dismissed after the excess cement has been removed.

       7- On the stone die made from the individual impression, a thin,
autopolymerizing resin coping will be formed with a brush technique.

       8- The wax pattern buildup on the resin coping is usually not begun until
the patient returns.

       9- the occlusal portion of the wax pattern is established by having the
patient close into maximum intercuspation, followed by excursive movements.
The wax pattern is returned to the cast, and additions are made as required to



                                                                Mostafa Fayad 34
                                                               Mouth preparation


dull areas. The process is repeated until a smooth occlusal registration has been
obtained.

       10- addition of sufficient wax to establish contact relations with the
adjacent tooth. At this time, the occlusal relation of the marginal ridges also
must be established.

       11- wax is added to buccal and lingual surfaces where the clasp arms
will contact the crown, and the wax pattern is again reseated in the mouth.

       12- The clasp arms,minor connectors, and occlusal rests involved on the
removable partial denture are carefully warmed with a needlepoint flame,
carefully avoiding any adjacent resin, and the removable partial denture is
positioned in the mouth and onto the wax pattern.

       13- Several attempts may be necessaryuntil the removable partial
denture is fully seated and the components of the clasp are clearly recorded in
the wax pattern.

       14- the temporary crown may be replaced and the patient dismissed.The
crown pattern is completed on the die by narrowing the occlusal surface
buccolingually, adding grooves and spillways, and refining the margins.

       15-Any wax ledge remaining below the reciprocal clasp arm may be left
to provide some of the advantages of a crown ledge. Excess wax remaining
below the retentive clasp arm, however, must be removed to permit the
addition of a retentive undercut later.

       16- The wax pattern must be sprued with care so that essential areas on
the pattern are not destroyed. After casting, the crown should be subjected to a
minimum of polishing, because the exact form of the axial and occlusal
surfaces must be maintained.

       17- After the crown has been tried in the mouth with the denture in
place, the location of the retentive clasp terminal is identified by scoring the


                                                                Mostafa Fayad 35
                                                                Mouth preparation


crown with a sharp instrument. Then the crown may be ground and polished
slightly in this area to create a retentive undercut.

       Ideally, all abutment teeth would best be protected with complete
crowns before the removable partial denture is fabricated. Except for the
possibility of recurrent caries because of defective crown margins or gingival
recession, abutment teeth so protected may be expected to give many years of
satisfactory service in the support, stabilization, and retention of the removable
partial denture.




                                                                 Mostafa Fayad 36
                                                            IMPRESSIONS FOR RPD


IMPRESSIONS FOR REMOVABLE PARTIAL DENTURE

                    A- PRIMARY IMPRESSIONS

Primary impressions are used in the preparation of study casts which playa vital
role in the planning and construction of a removable partial denture.

Stock tray

       The stock tray used for the primary impression should be

       1- large enough to provide adequate thickness of the alginate
impression material (5- 7 mm).

       2- Has a mechanical means of retention of impression material.

       If the maxillary arch has a high vault, build up the tray with impression
compound to prevent the hydrocolloid from sagging away from the palatal
surface. The margins of the stock tray may need to be lengthened with
impression compound or it may need to be trimmed.




I-Irreversible hydrocolloid (Alginate): -

       Common problems in making alginate impressions:

1-Surface inaccuracy due to:

  a- Air bubbles.

  b- Mucous film on the soft tissue.

2- Dimensional inaccuracy due to:

   a- synerisis & imbibition.

   b- strain caused by movement or removal during gelation.



                                                                  Mostafa Fayad 1
                                                             IMPRESSIONS FOR RPD


   c- dislodgment of impression from the tray.

   d- displacement during pouring.

3- Cast has rough surface or chalky appearance:due to

   a- insufficient spatulation of stone.

   b- saliva retained on impression.

   c- poor mix of alginate.

   d- impression left long period in contact wit the cast.

   e- trapping of air.

4- Low tear strength of alginate.

   This may be improved by lifting the impression in the patient mouth one or
two minutes more after setting.

Advantages of alginate:

1-can be used with the presence of saliva.

2-pour well with stone (hydrophilic).

3-has pleasant taste and odor and non expensive.

4-Can be disinfected with 2% glutaraldehyde stored in 100% humidity and
poured within one hour.




Possible Causes of an Inaccurate and/or a Weak Cast of a Dental Arch

1. Distortion of the hydrocolloid impression (a) by use of an impression tray
that is not rigid; (b) by partial dislodgment from the tray; (c) by shrinkage
caused by dehydration; (d) by expansion caused by imbibition (this will be




                                                                  Mostafa Fayad 2
                                                               IMPRESSIONS FOR RPD


toward the teeth and will result in an undersized rather than oversized cast);
and (e) by attempting to pour the cast with stone that has already begun to set.

2. A ratio of water to powder that is too high. Although this may not cause
volumetric changes in the size of the cast, it will result in a weak cast.

3. Improper mixing. This also results in a weak cast or one with a chalky
surface.

4. Trapping of air, either in the mix or in pouring, because of insufficient
vibration.

5. Soft or chalky cast surface that results from the retarding action of the
hydrocolloid or the absorption of necessary water for crystallization by the
dehydrating hydrocolloid.

6. Premature separation of the cast from the impression.

7. Failure to separate the cast from the impression for an extended period.

                      B- FINAL IMPRESSION
               ANATOMICAL FORM FINAL IMPRESSION
                      FOR TOOTH SUPPORTED R P D

        The anatomic form impression is a one-stage impression method using
an elastic impression material that will produce a cast that does not represent a
functional relationship between the various supporting structures of the
partially edentulous mouth. It will only represent the hard and soft tissue at
rest.

        A removable partial denture fabricated from a one stage impression,
which only records the anatomic form of basal seat tissue, places more of the
masticatory load on the abutment teeth and that part of the bone that underlies
the distal end of the extension base.

Technique of making anatomical final impression:

                                                                     Mostafa Fayad 3
                                                          IMPRESSIONS FOR RPD


I. Position of patient and dentist:

II. Verifying and adjusting special impression tray:

III. Mixing impression material:

IV. Loading impression tray:

V. Making the impression:

VI. Removal of impression from the mouth:

VII. Inspecting the impression:

VIII. Cleaning the impression:

IX. Pouring of the cast:

X. Trimming the cast:

Rubber base impression materials:

Advantages:

1- greater dimensional stability.

2- produces a smooth surfaces of the stone cast.

3- higher tear strength.

Types:

A- Mercaptan(Thiokol or polysulphide):-

Indication:

Final impression for RPD & for altered cast impression.

Advantages:

1- longer setting time than alginate , which gives a chance for a better border
molding.

                                                                Mostafa Fayad 4
                                                              IMPRESSIONS FOR RPD


2- hydrophobic so it can be disinfected in liquid (cold sterilizing solutions).

Disadvantages:

1- the medium and heavy body materials do not recover well from deformation
and so should not be used when large undercuts are present.

2- the long term of dimensional stability of these materials is poor due to water
loss after setting.

It should allowed to rebound foe 7-15 minutes then poured immediately.

B- Silicone:

Indications:

1- final impression for RPD and for altered cast impression.

2- can be used with a compatible putty in a double impression tech.

Advantages:

1- the most accurate elastic impression material (addition type).

2- moderate working time (can be controlled by amount of accelerator).

3- pleasant odor.

4- excellent recovery from deformation.

5- disinfected in sterilizing solutions.

6- the addition reaction silicones can be poured up to one week. While the
condensation reaction silicones should be poured within one hour.

Disadvantages:

1- latex gloves inhibit polymerization of some silicones.

2- the putty forms are expensive and of short shelf life.



                                                                    Mostafa Fayad 5
                                                              IMPRESSIONS FOR RPD


C- polyether:

Indications:

in addition to its use as an impression material it can be used as a border
molding material. However, it is not compatible with the addition reaction
silicone and should not be used for border molding with it.

Advantages:

1- good wetability that produces easy cast forming (hydrophilic).

2- it should be poured within 2 hours ; however if it is kept dry it can be poured
within 7 days.

Disadvantages:

1- Shorter working and setting time.

2- The flow and flexibility are the lowest, which may cause cast breakage
during removal from the impression.

Master cast:

- It the cast obtained from pouring the final impression.

- The impression is poured in two stages; in the first stage the stone is vibrated
into the impression until it is filled.

After initial setting of this layer, the second stage is start for making a base for
the cast.

Removal of cast from impression:

- Stone should be allowed to set for 45 minutes before separating the cast from
the impression.

- The cast is trimmed by a cast trimmer.



                                                                     Mostafa Fayad 6
                                                              IMPRESSIONS FOR RPD


- The cast is rejected if voids or nodules of stones are found in a critical areas
e.g. rest seat area.

                       Special Impression Techniques

                   FOR TOOTH TSSUE SUPPORTED R P D

Objective:

          When occlusal forces are applied to a tooth-supported removable partial
denture, they are directed through the rests and
transmitted to the abutments.

          The edentulous ridges do not contribute to
the support of the RPD because the teeth absorb
these forces before the forces can be transmitted
to the underlying residual ridge.

      Since the denture base does not contribute to the support of the partial
denture and the underlying mucosa and bone are not subjected to functional
forces,     a   tooth-supported     RPD      can   be
constructed on a master cast made from a single
impression that record the teeth and soft tissues
in their anatomic form.

          When occlusal forces are applied to a tooth-tissue-supported RPD, these
forces must be equally distributed to the abutments and the tissues of the ridge.
So a dual impression technique is used in which a (corrected cast) is generated.

          The impression of teeth is made with a material that records the teeth in
their anatomic positions, while the impression of the residual ridge must record
the soft tissues in their functional form.




                                                                    Mostafa Fayad 7
                                                               IMPRESSIONS FOR RPD


Aims of Dual Impression Technique:

   1. Record and relate the tissues under uniform loading.

   2. Distribute the load over as large an area as possible.

   3. Accurate determination of the peripheral extent of the denture base.

Factors influencing support of distal extension base : see class 1 design

Requirements of accepted impression for distal extension base:

          An impression registration for the fabrication of a partial denture must
fulfill the following two requirements:

1. The anatomic form and the relationship of the remaining teeth in the dental
arch and the surrounding soft tissue must be recorded accurately so that the
denture will not exert pressure on those structures beyond their physiological
limits.

          A type of impression material that can be removed from undercut areas
without permanent distortion must be used to fulfill this requirement. The
elastic     impression materials, such as irreversible hydrocolloid (alginate),
mercaptan rubber base (Thiokol), silicone impression materials (both
condensation and addition reaction), and the polyethers are best suited for this
purpose.




2. The supporting form of the soft tissue underlying the distal extension base of
the partial denture should be recorded so that firm areas are used as primary
stress-bearing areas and readily displaceable tissues are not overloaded. Only in
this way can maximum support be obtained for the partial denture base. An
impression material capable of displacing tissue sufficiently to register the
supporting form of the ridge will fulfill this second requirement. A fluid
mouth-temperature wax or any of the readily flowing impression materials


                                                                    Mostafa Fayad 8
                                                             IMPRESSIONS FOR RPD


(rubber base, silicones, or polyethers in an individual, corrected tray) may be
employed for registering the supporting form. Zinc oxideeugenol paste can also
be used when only the extension base area is involved in the impression .

        No single impression material can satisfactorily fulfill both of the
previously mentioned requirements.

        Recording the anatomic form of both teeth and supporting tissue will
result in inadequate support for the distal extension base. This is because the
cast will not represent the optimum coordinating forms, which necessitates that
the ridge be related to the teeth in a supportive form. This coordination of
support maximizes the support capacity for the arch and minimizes movement
of the partial denture under function.

Three factors must be considered in the acceptance of an impression
technique for distal extension removable partial dentures:

     1- The material should record the tissue covering the primary stress
         bearing areas in their function form.

     2- Tissues within the basal set area other than the primary stress bearing
         areas must be recorded in their anatomic form.

     3- Maximum coverage by the impression must be obtained to distribute
         the lode over as large an area as can be tolerated by the border tissues.
         This is an application of the principle of the snowshoe.

  Indications of dual impression technique:

1-    In mandibular distal extension ridge, because

        a)- there is only a limited ridge area can be used as a primary stress
        bearing area.

        b) – Difficult to obtaining the proper peripheral extension for denture
        base, because a movable tissues in the flower of the mouth.


                                                                    Mostafa Fayad 9
                                                            IMPRESSIONS FOR RPD


     In the maxillary arch the dual impression does not often improve the
stress distribution. Because, the maxillary distal extension ridge is usually
covered by a firm, dense will attached mucosal the stress bearing area must be
the crest & buccal slope of the ridge.

2-   Long span anterior edentulous ridge where the ridge must supply some
     support for the partial denture.

 A dual impression technique is used to equalized as much as possible the
support derived from the edentulous ridge& that received from the abutment
teeth.

Impression methods

A – Physiologic or functional impression techniques.

            McLean's physiologic impression technique (made before the
              framework construction)

            Hindel's impression technique (made before the framework
              construction)

            The Functional Relining method ( made after finishing of RPD ) .

            The fluid wax functional impression technique (made after the
              framework construction )

B- selected pressure impression.

         a- Two stage selected pressure impression technique.

         b- One stage selected pressure impression technique

The Altered Cast Techniques

         a-The fluid wax functional impression technique.

         b- Two stage selected pressure impression technique


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                                                           IMPRESSIONS FOR RPD




I- Physiologic or functional impression techniques:

   1- McLean's physiologic impression technique:-

  In this technique the impression of the edentulous areas was made with
impression past loaded in an acrylic tray which was providing with occlusion
rim under biting force.

       This impression was then related to the arch by making a hydrocolloid
impression (overall impression) with the original impression set in the mouth.
After removal the composite impression from the mouth a master cast was
poured with the edentulous areas recorded under functional loading.

Disadvantages: -     The tray used for over all impression was in contact with
the occlusion rims of the original impression & held in his position with finger
pressure. This pressure does not simulate the occlusal loading. This lead to the
advantage of the technique was lost with this variation.

    2- Hindel's impression technique:

     in Hindel's technique the imp of the edentulous ridge was not made under
pressure but it is an anatomic imp made with a free-flowing zinc oxide-eugenol
paste. After setting of the impression, a tray with ¾ inch holes in the regions
of the first molar for the second impression is made. So that finger pressure
could be applied through this holes of the tray as the hydrocolloid impression
was made. The pressure had to be maintained until the alginate was completely
set. The finished impression was a reproduction of the anatomic surface ridge
and the surface of the teeth.

                                                                Mostafa Fayad 11
                                                                IMPRESSIONS FOR RPD


         The main purpose of these techniques was to relate an impression of the
edentulous ridge to the teeth under a form of function loading (supported
form).




Disadvantages:

         A- If the action of the retentive clasps of the partial denture is sufficient
to maintain the denture base in relation to the soft tissue in the functional form,
this lead to interruption of blood circulation & resorption of the under lying
bone.

         B- If functional relationship of the denture base to the soft       tissue is
present when the partial denture at rest, this lead to, the partial denture would
be slightly occlusal than the remaining teeth and premature contact occurred.

3- Functional relining method

         The functional relining is done to a completed partial denture
constructed on a cast made from a single impression. It can be used before
initial insertion for the purpose of perfecting the fit of the denture base to the
residual ridge.

         If relining is planned, a soft metal spacer (ash No 7) is adapted over the
ridge on the cast before processing the denture base. After processing, the
metal is removed, leaving an even space between the base and the edentulous
ridge to allow room for the impression material.

         It can also be used for relining an old partial denture to compensate for
bone resorption.

         In making the reline impression, the patient must maintain the mouth in
a partially opened position while the border molding and impression are being


                                                                     Mostafa Fayad 12
                                                             IMPRESSIONS FOR RPD


accomplished because the relationship between the partial denture framework
and the teeth must be observed.

       A low fusing compound is used to make an impression for the
edentulous ridge. Then the entire surface of the modeling plastic is scraped to a
depth of 1mm. The final impression is made with a free flowing zinc oxide
paste. If undercuts are present on the ridge light bodied polysulphide or silicon
may be used.

       b)      Impression making:

             Placed a flowing law-fusing modeling plastic over the tissue
               surface of the denture base.

             Tempering the modeling plastic in a water bath, and seating in
               the patient’s mouth.

             The heating, tempering, and seating must be accomplished
               several times until; accurate imp of the ridge is made.

             The border extensions are determined by limiting application of
               heat to the borders& manipulating he cheek & tongue.

             The modeling plastic over ridge is relieved before final imp is
               made to provide space for the imp material. This relived
               approximately 1mm, or the entire thickness of the modeling
               plastic may be removed over the crest of the ridge.

             The final imp is made with a free-flowing Z.D.E. paste. If
               undercut are present on the ridge, light-bodied rubber base may
               be used.

             As in all reline procedures, occlusal discrepancies must be
               corrected. Because, the open mouth imp technique must be used
               it is impossible to maintain previously established occlusal
               contacts. If error in occlusion after the denture had been

                                                                     Mostafa Fayad 13
                                                             IMPRESSIONS FOR RPD


              processed is slight, the correction may be accomplished in the
              mouth. However, in a majority of cases it will be necessary to
              remount the partial denture on an articulator to correct & refine
              occlusion.




Disadvantage of functional relining:

After relining occlusal discrepancies occurs.

Advantage of functional relining :

       a) Improving the fit of the denture base to the residual ridge.

       b) Control the amount of soft tissue displacement by controlling the
amount of relief of the modeling plastic before impression making. The greater
the relief the less will be the tissue displacement.




4- The fluid wax functional impression technique: see later

II – The Altered Cast Techniques

       The selected pressure impression technique and the fluid wax functional
impression are made after the framework construction for the purpose of
correcting the master cast before processing the denture base ( Altered cast
technique ) . The framework is constructed on a master cast made from a
single impression .

a- The fluid wax functional impression technique :

             The term fluid wax is used to denote waxes that are firm at room
temperature & have the ability to flow at mouth temperature.

The most frequently used fluid waxes are (Lowa wax & korrecta wax No.4.)
The korrecta wax is lightly more fluid than Lowa wax.


                                                                   Mostafa Fayad 14
                                                           IMPRESSIONS FOR RPD


       The objectives of these techniques are:

1-      To obtain maximum extension of the peripheral borders of the denture
base without interfering with the function of movable border tissue.

2-     To record the stress-bearing area of the ridge in their functional form,
and to record non-pressure bearing areas in their anatomic form. This technique
made with the patient opened his mouth this lead to less changer of
displacement of ridge by occlusal or vertical forces.

     Impression technique

      1- Autopolymerizing acrylic resin custom tray is made over the
     edentulous ridge framework .

     2- Green stick compound is used for border molding the impression tray .

     3- Relieving the tray and impression making , relief between the tray
     and the ridge of 1-2 mm is provided .

     4- Iowa or Korrecta wax No 4, molten in a water bath is painted on the
     tray with a brush.

     5-The tray is seated in the mouth for about 5 minutes, while the patient’s
     mouth is kept opened. The patient is instructed to do functional
     movements and border trimming is made .

     6-The impression is removed, dried and inspected. Where tissue contact is
     present the wax surface will be glossy and where there is no contact the
     surface will be dull.

     7-Any dull spots or imperfections are coated with wax and the procedure
     is repeated. The entire surface of completed impression should have a
     glossy appearance and all peripheral margins are definitely turned over.




                                                                Mostafa Fayad 15
                                                           IMPRESSIONS FOR RPD


     8- When the impression is completed, it should be left in the mouth for 12
     minutes to be certain that the wax has completely flowed and releasing
     any pressure that may be present.




b-The selected pressure impression technique:

      it is often referred to as the " Selective Tissue Placement Impression" or
"dynamic" impression. to selectively recording of mucoosseous tissue we use

      1- Varying viscosity of impression material

      2- Selective venting (escape hole) of tray

      3- Selective relief of the tray

Method:

   1- Autopolymerizing acrylic custom tray is made over the edentulous ridge
      framework.     Green stick compound is used for border molding the
      impression tray.

   2- The mandibular tray is relieved at specific area of the ridge as the crest
      of the ridge down to the metal . Only slight relief is provided in the
      buccal shelf and lingual slope areas . The tray may be vented over the
      ridge crest to allow escape of the impression material and decrease
      tissue displacement. Impression is made with zinc oxide paste if the
      ridge is free from gross      undercuts . Both polysulphide and silicon
      impression materials are indicated for those ridges with bony undercuts.

Framework try in

Before the trays are attached, the framework must be fitted in the mouth.

1. Use of a disclosing media to identify interferences to completely seating the
removable partial denture framework


                                                                Mostafa Fayad 16
                                                            IMPRESSIONS FOR RPD


2. Use of disclosing media to identify the appropriate contact(s) of the
component parts of the framework during the seating of the framework and
when the framework is completely seated in its designated terminal position

3. Adjusting the seated framework to the opposing occlusion. If there are
opposing frameworks, the maxillary framework is removed from the mouth
and the mandibular framework is adjusted to the natural maxillary dentition.
Then the maxillary framework is replaced and it is adjusted to the mandibular

       Several types of disclosing media may be used, such as stencil
correction fluid, rouge and chloroform, and disclosing fluids, pastes, a spray
disclosing medium and waxes. the framework is placed with mild pressure.

Making impression tray

           1- The metal framework & the master cast must be examined to
              eliminate any obliteration in the lingual extension of a
              mandibular ridge by trapped of the floor of the mouth or
              sublingual gland within the impression.

N.B: One reason for modifying the impression tray with molding plastic is to
prevent the trapping of the floor of the mouth or the sublingual gland within the
impression.

           2- The acrylic resin impression tray then adapted & contoured
              without any relief at this time. Because the tray should
              stabilized during border modeling.

       Obtaining support from the primary support areas is achieved by:
the manner in which the flow of the impression material is controlled during
the impression-making procedure.

       Restricting the flow of the material in the primary stress-bearing areas
(by minimizing the amount of relief over the area when the custom tray was
made) causes greater pressure to be exerted on the tissue in this area (compared

                                                                 Mostafa Fayad 17
                                                            IMPRESSIONS FOR RPD


with other areas of unrestricted flow where a greater amount of relief or
venting of the impression tray was provided).

B – Correcting peripheral extensions of tray:

          1- The framework with the tray attached is seated in the mouth.

The buccal extension of the tray should be observed as the cheek is moved
down word, outward and upward, the edge of the tray should be just shy (1 or
2mm) of the movable tissue.

          2- The posterior extension of the tray should be end at two thirds
             coverage of the retro molar pad to be directly observed.

          3- The distoligual extension of the tray is determined by the patient
             protruding his tongue until contact the upper lip. The fingers of
             the operator should be rest lightly on the tray, if the tray tends to
             lift, even slightly, during this movement, the distolingual length
             should be shortened.

          4- The patient moves the tongue into each cheek with the operator
             fingers resting lightly on the tray to check the lingual flange
             extension. If the tray moves during this movement, the lingual
             flange opposite the cheek toward which the tongue moves, should
             be shortened.




C- Border molding the Impression tray:

        The tray may be border molded in two steps:

          1- From the anterior extent of the buccal flange to the most posterior
             extent of the tray.

          2- The remaining of the lingual & distolingual flange:



                                                                  Mostafa Fayad 18
                                                             IMPRESSIONS FOR RPD


         A low – fusing modeling plastic, green or gray stick, is used for this
procedure. This step will be as in correcting the peripheral extension. This
processes basically the same as that for complete denture.

D – Relieving trays:

          Now the relief under the tray is done at specific area needed .

Correcting the master cast

   1- The ridge area(s) of the cast , which will be replaced by corrected cast
       impression , is outlined with a pencil and removed with a handsaw .
       Retentive grooves on the cut surface of the cast are made. These grooves
       will help in retention of the poured new stone to the old cast .

   2- The framework with the impression is seated and sealed to the sectioned
       cast .

   3- The sectioned cast with the impression is inverted , beaded , boxed and
       poured into dental stone .

The resultant cast is used to complete the partial denture . The tissue
displacement during impression requires that the metal stop should be adapted
to the cast by self – curing resin before making the record base .




                                                                     Mostafa Fayad 19
                                                                     IMPRESSIONS FOR RPD




Areas to be removed from the cast are outlined , removed & retentive grooves are made to
                help in retention of the poured new stone to the old cast .




                                                                              Mostafa Fayad 20
                                                                IMPRESSIONS FOR RPD




Beading & boxing of the impression .              The corrected cast after hardening of
dental stone.

                       Steps for correcting the master cast .




                                                                     Mostafa Fayad 21
                                                           IMPRESSIONS FOR RPD


        The selective pressure technique described above can be applied to all
varieties of residual ridges as it is customized to mucosal conditions, whereas
the functional impression technique has limited application to a uniformly firm
ridge consistency.

II- One stage selected pressure impression technique:

        Dumbrigue and esquivel in 1998 described a technique for selective
pressure impression technique from a single impression prior to framework
construction and after mouth preparation.

Procedure:

1- A custom tray with 2 mm. Short borders is constructed over the study cast
after adaptation of two layer wax on teeth and residual ridge. Aluminium foil is
burnished over the wax.

2- Occlusal stops are placed over the remaining teeth by cutting boxes through
the aluminium foil and wax to ensure proper seating of the tray.

3- Softened modelling compound is applied in the tissue surface of the tray.

4- Reheat compound and place intraorally. Remove, check and then apply
modelling compound to the border

5- Relief the tissue surface of compound 1mm except for primary stress bearing
area.

6- Make complete impression using rubber base material with applying finger
pressure.




                                                                   Mostafa Fayad 22
                                                               IMPRESSIONS FOR RPD


Control of gagging

Procedures that will help to prevent gagging include:

1. The dentist should:

        a) Not mention the subject of gagging

        b) Ask whether the patient has had impressions made previously.

2. Before the impression is made:

        a) Ask the patient to use astringent mouth rinse and cold-water rinses

        b) Seat the patient in an upright position with the occlusal plane
        parallel with the floor.

        c) Ask the patient to take a deep breath and hold the breath while the
        dentist quickly checks the size and fit of the tray.

        d) Correct the maxillary tray with modeling plastic and leaving
        sufficient unrelieved modelling plastic at the posterior border.

3. The impression material must:

        a) Have the consistency of thick whipped cream

        b) Fast-setting alginate.

        c) Set up to a rubbery consistency in few minutes.

4. During the impression procedure:

        a) Not overfill the tray with impression material.

        b) Seat the posterior part of the tray first and then rotate the tray into
        position.

        c) Force excess alginate in an anterior direction.



                                                                   Mostafa Fayad 23
                                                                IMPRESSIONS FOR RPD


        d) Ask the patient to: • Keep the eyes opened and focused on some
        small object. • Breathe through the nose.

5. The “leg lift” procedure is used before and during the making of the
impression.

6. Giving all instructions to the patient in a firm, controlled manner.

7. The use of an anesthetic spray is usually contraindicated.




Control of saliva
If the teeth are too dry, alginate has a tendency to stick to them. Therefore the
teeth should not be air dried before making an impression.

Excessive amounts of saliva, particularly of the thick mucous type, will
displace the alginate impression material and will contribute to an inaccurate
impression.

The excessive saliva can be controlled for most patients by having the
patient rinse the mouth with an astringent mouthwash followed by a rinse
of cold water and then packing the mouth with unfolded 2 x 2 inch gauze:

• In the maxillary arch one gauze strip is placed in the right buccal vestibule
and another in the left vestibule. The dentist must wipe the palatal area just
before making the impression.

• In the mandibular arch one gauze strip is placed in each of the buccal
vestibules and another is placed in the linguoalveolar sulcus by having the
patient raise the tongue, placing the gauze in the sulcus, and then having the
patient relax the tongue to hold the gauze in position. The gauze is removed
immediately before the impression is made.

• With excessive amount of thick mucinous saliva from the palatal salivary
glands, the patients should be instructed to rinse with an astringent mouth rinse.

                                                                    Mostafa Fayad 24
                                                          IMPRESSIONS FOR RPD


Then 2 x 2-inch sponges moistened in warm water should be used to place
pressure over the posterior palate in an attempt to milk the glands. This is
followed by an ice water rinse immediately before the impression is made.

• With copious amounts of saliva, the use of an antisialagogue in combination
with mouth rinses and gauze packs effectively controls this salivation. (A 15-
mg Pro-Banthine tablet taken 30 minutes before the impression appointment)




                                                               Mostafa Fayad 25
                                                     Establishing occlusal relationship


              ESTABLISHING OCCLUSAL RELATIONSHIPS

       Establishing of functional, and harmonious occlusion is important in the
treatment of partially edentulous patients. Occlusal harmony between a partial
denture and the remaining natural teeth is a major factor in the preservation of
the residual ridges, and the abutment teeth.

       The goal in developing an occlusal scheme for the R P D to provide a
masticatory efficiency & esthetically acceptable, and to distributed the occlusal
loading as evenly as possible to all supporting structures in case of tooth tissue
born R P D.

       DESIRABLE OCCLUSAL CONTACT RELATIONSHIP FOR
REMOVABLE PARTIAL DENTURES;

   •   The following occlusal arrangements are recommended to develop a
       harmonous occlusal relationship of removable partial dentures and to
       enhance stability of the removable partial dentures

   1. Simultaneously bilateral contacts of opposing posterior teeth must occur
       in centric occlusion

   2. Occlusion for tooth supporetd removable partial denture may be arranged
       similar to the occlusion in seen in a harmonous natural dentition

       -      Stability of such removable partial dentures results from the effect
of the direct retainers at tha both ends of the dentures base

       3.Bilateral balanced occlusion in eccentric position should be formulated
when a maxillary complete denture oppose the removable partial denture. This is
a complete primarily to promote the stability of the complete denture.

       4. Working side contact should be obtained for the mandibular distal
extension denture. This contacts should occur simultaneously with working side
contacts of the natural teeth to distribute the stress over the greatest possible area




                                                                       Mostafa Fayad 1
                                                    Establishing occlusal relationship


       5. Simultaneously working and balancing contact should be formulated for
the maxillary bilateral distal extension removable partial denture whenever
possibe.

       6. Only working contacts need to be formulated for either maxillary or
mandibular unilateral distal extension removable partial dentures.

       7. In the Kennedy Class IV removable partial denture configuration
contact of opposing anterior teeth in the planned intercuspal position is desired to
prevent a continous eruption of the opposing natural incisors unless they are
otherwise prevented from extrusion by means of a lingual plate, auxillary bar, by
splinting.

       8. Balanced contact of opposing posterior teeth in a straight forward
protusive relationship and functional excursive position is desired only when an
opposing complete denture or bilateral distal extension maxillary removable
partial denture is placed.

       9. Artificial posterior teeth should not be arranged further distally than the
beginning of a sharp upward incline of the mandibular residual ridge or over the
retromolar pad.

Failure to provide and maintain adequate occlusion on the removable
partial denture is primarily a result of:

       (1) Lack of support for the denture base,

       (2) The fallacy of establishing occlusion to a single static jaw relation
record.

          (3) An unacceptable occlusal plane.

The establishment of a satisfactory occlusion for the removable partial
denture patient should include the following:

       (1) An analysis of the existing occlusion;

       (2) The correction of existing occlusal disharmony;

                                                                      Mostafa Fayad 2
                                                    Establishing occlusal relationship


       (3) The recording of centric relation or an adjusted centric occlusion;

       (4) The recording of eccentric jaw relations or functional eccentric
occlusion; and

       (5) The correction of occlusal discrepancies created by the fit of the
framework and in processing the removable partial denture.




                           Vertical Jaw Relation

Vertical diminution (V D) :-

Definition:- it is a vertical measurement of the face between two arbitrary points :
one below the mouth usually on the chin, and other above the mouth generally on
the nose.

Two vertical dimensions are recognized for each patient:-

   1- Vertical dimension of rest (V D R): - it is taking when the patient is in an
       upright position and is complete at rest, and the natural teeth will not be
       touching (free way space).

   2- Vertical dimension of occlusion (V D O): - it is taking when the patient
       with natural teeth elevates the mandible from the rest position and the
       teeth become contact in maximum intercuspal relation.

Altering the Vertical Dimension of Occlusion:-

   For most patients requiring RPD measurement of the V D is not necessary. As
the following:-

       If natural teeth in opposing arch contact in C O. This should be
considered as a V D O for that patient, and the prosthesis should be constructed
at this V D. increasing this V D O should be occur only; if the patient display
symptoms that suggested the V D O has been dimensioned, shush as tired aching



                                                                      Mostafa Fayad 3
                                                    Establishing occlusal relationship


muscles, unexplained pain in the head or neck, or an appearance of premature
aging caused by shorting nose-chin distance

Most significance signs of over closure:-

1- Excessive free –way space.

2- Extrem anterior vertical overlap in which the mandibular teeth actually strike
the soft tissue of the palate and migration of the condyles (this seen in
radiographically).

- If these signs and symptoms are present, a temporary increase in existing V D
can be considered with a temporary removable appliance in the form of an
acrylic resin occlusal overlay to cover the maxillary teeth. Because less
interference with the tongue movement. The most importance consideration is
the remaining teeth in both arches must be contact by the prosthesis.

-If the teeth not in contact by the appliance; will tend to erupted to reestablished
the functional contact. - If sufficient number of remaining teeth is not used to
support the appliance, the supporting teeth will be submerged or depressed to an
infraocclusal position.

- If the physiologic response of the patient to this appliance is positive disappears
the signs & symptoms of the decreased V D for several months, permanent
correction must be instituted.

      When permanent treatment begins, it must be planned so that all occlusal
dimension restoring prosthesis, fixed and removable, are inserted at the same
time.



Establishing V D O:-

       Only a small percentage of partially edentulous patient( those who have C
D opposed P D & those who have lost all posterior teeth in one or both arch)
need to have the V D O established by measurement. This done by measuring the
V D R and then subtracting 3 mm (the average amount of free way space).

                                                                      Mostafa Fayad 4
                                                     Establishing occlusal relationship


                        Horizontal jaw relationship

        Two horizontal jaw relationships of mandible to maxilla are of importance
in the occlusion of R P D.

a- The first of these relationships of the mandible to maxilla is centric relation
(CR).

b- The second of these relationships is centric occlusion (C O). In more than
90% of all people, C R & C O does not coincide. The C O will always be anterior
to the C R 1 to 2 mm is most frequently. The patient with partial denture will
always function in these two positions & intervening space, so deflective
occlusal contacts in either position must be avoided.

    Deflective occlusal contacts:- it is a contact that displaces a tooth, diverts the
mandible from it is intended movement, or displaces the removable denture from
it is basal seat.




Selection of C R or C O in recording horizontal jaw relation:-

1- C R & C O position coincide with no evidence of occlusal pathology;
therefore the decision should be to fabricate the restoration in centric relation;

2- C R & the C O position do not coincide but the planned C O position is clearly
denned and the decision has been made to fabricate the restoration in the planned
intercuspal position;

3- C R & the planned C O position do not coincide and the intercuspal position is
not clearly denned, therefore the decision should be made to fabricate the
restoration in centric relation;

4- Posterior teeth are not present in one or both arches and the denture will be
fabricated in centric relation.


                                                                       Mostafa Fayad 5
                                                     Establishing occlusal relationship


Factors influencing development of occlusion

Several factors influence the final occlusal schem for the partial denture patient.
(Hanau Quint)

1. The inclination of the condylar guidance.

2. The prominence of the compensating curve.

3. The inclination of the plane of orientation.

4. The inclination of the incisal guidance.

5. The heights of cusps.

   In a patient who has partial dentures, however, the factors governing the
occlusal patterns are already determined.

The presence of some natural teeth means that the prominence of the
compensating curve has been determined& the plane of orientation is present.

 The presence of anterior teeth means that the incisal guidance is determined
and the height of the cusps is known.

 This means that in partial denture construction the remaining natural teeth will
dictate the form and position of the artificial teeth. The only exceptions are:

1. When the removable partial denture is opposed by a complete denture and
occlusal harmony can be obtained and

2. When only anterior teeth remain in both arches and the incisal relationship is
noninterfering.




       METHODS FOR ESTABLISHING OCCLUSSAL RELATIONSHIP

There are basically two methods of establishing the occlusion for a removable
partial denture:


                                                                       Mostafa Fayad 6
                                                     Establishing occlusal relationship


1. The articulator, or static, technique.

2. The functionally generated path technique

I- Articulator Technique

       1- Direct Apposition of Casts (Hand Articulation)

     Hand articulation may be used when sufficient opposing teeth remain in
contact to make the existing jaw relation ship obvious.

       It should be used when only a few teeth are to be replaced.

       The occluded casts are secured together with wooden sticks and sticky
wax and mounted arbitrarily on an articulator. A face-bow mounting is generally
not indicated.

The limitations to using this method:-

   The principal danger in this technique is that it perpetuates the existing
vertical dimension and any existing occlusal disharmony.

3- Interocclusal records with posterior teeth remaining

- It is a modification to the direct apposition of cast. It is used when sufficient
teeth remain to support the partial denture (Kennedy class III or Class IV), but
the relation of opposing teeth does not permit the occluding of casts.

a- Interocclusal wax records:

- A uniformly softened, metal-reinforced baseplate or set-up wax is placed
between the teeth, and the patient is guided to close in centric relation.

- The wax is then removed & immediately chilled
thoroughly in room–temperature water. It should be
replaced a second time to correct the distortion that
result from chilling & then again chilled after removal.



                                                                       Mostafa Fayad 7
                                                      Establishing occlusal relationship


- All excess wax should now be removed with a sharp knife. All wax that
contacts mucosal surfaces be trimmed free of contact. The chilled wax record
again should be replaced to make sure that no contact with soft tissue exists.

- A wax record should be further corrected with a bite registration paste,
which is used as the final recording medium. The bite registration paste is then
mixed and applied to both sides of the metal reinforced wax record. The patient
is assisted with closing in the rehearsed path, which will time be guided by the
previous wax record. After the paste has set, the corrected wax record is removed
and inspected for accuracy.

     The record should seat on accurate casts without discrepancy or
interference. When an intact opposing arch is present, use of an opposing cast
may not be necessary. Instead, a hard stone may be poured directly into the
impression paste record to serve as an opposing cast.

       The advantage of having casts properly oriented on a suitable articulator
contraindicates the practice. The only exception to this is if the maxillary cast on
which the partial denture is to be fabricated has been mounted previously with
the aid of a face-bow. In such an instance an intact lower arch may be reproduced
in stone by pouring a cast directly into the interocclusal record.

-    The advantages of using a metallic oxide paste over wax as a recording
medium for occlusal records

       1- Uniformity of consistency.

       2- Ease of displacement on closure.

       3- Accuracy of occlusal surface reproduction.

       4- Dimensional stability.

       5- The possibility of some modification in occlusal relationship after
       closure, if it is made before the material sets.

       6- Less likelihood of distortion during mounting procedures.

                                                                        Mostafa Fayad 8
                                                   Establishing occlusal relationship


Three important details to be observed when one uses such a material:

       1- Make sure that the occlusion is satisfactory before making the
       interocclusal record.

       2- Be sure that the casts are accurate reproductions of the teeth being
       recorded.

       3- Trimmed the record with a sharp knife wherever it engages undercuts,
       soft tissues, or deep grooves.

B-Using of bite tray:

A ready made bite tray may be used to record the jaw relation. The final
recording medium is placed on both sides of the tray and the patient is guided to
close in centric occlusion.

3 - Jaw Relation Record Made By Using The Framework

   In the first jaw relation record made to complete the diagnostic mounting
procedure, baseplates were used to transport occlusion rims and recording media.
The baseplates were constructed of autopolymerizing acrylic resin.

  For the final jaw relation record the framework should be used to support the
occlusion rim and recording medium.

1- The framework should be fit & any occlusal interference have been corrected
or eliminated at the framework try-in appointment. This means that the
framework will be a stable and accurate base on which to record the jaw
relationship.

2- If this appointment follows the construction of an altered or corrected cast, as
it usually will. The acrylic resin tray that was used to make the impression must
be removed from the framework. The impression should not be used as a
recording base for the jaw relation record because the impression generally is
distorted as it is removed from the cast.



                                                                     Mostafa Fayad 9
                                                   Establishing occlusal relationship




Lab procedures:-

a- Making the Record Base:-

  If the edentulous space is not too long, hard baseplate wax may be formed over
the acrylic resin retention metal in contact with the edentulous ridge. The normal
precautions must be taking during handling the framework, and using a pressure-
free interocclusal media, to decrease the pressure on the record base.

   The baseplate wax record base & the casts must be mounting on an
articulator immediately to avoid the distortion of the wax.

If the edentulous ridge is long or if the interarch space is restricted,
autopolymerizing acrylic resin (sprinkle-on method) or acrylic resin tray material
(finger-molding technique) should be used to construct the record base. But the
danger of damaging the master cast is also slightly greater.

Regardless of the material used to construct the record base, soft tissue undercuts
on the edentulous ridge must be blocked.

    Separating medium should be painted over the edentulous ridge before the
framework is seated.

       To prevent the dislodge the framework by excessive downward force
during the adaptation of the record base materials. A bead of autopolymerizing
resin can be placed between the tissues stops and the stone ridge and allow to set
before the record base is adapted.

b- Occlusion Rim

 An occlusion rim of medium baseplate wax is added to the record base. The
occlusion rim should be centered over the crest of the edentulous ridge. The
mandibular distal extension occlusion rim may be constructed so that the height
will be even with the cusps of the adjacent abutment tooth anteriorly and
posteriorly to two-thirds the height of the retro-molar or pear-shaped pad.

                                                                    Mostafa Fayad 10
                                                    Establishing occlusal relationship


c- Recording Media

1- Zinc oxide-eugenol impression paste it is the first choice as a recording
medium. It can be mixed to form a free-flowing, practically pressure-free
material. The material produces a firm record and not liable to damage. The
record can be kept for an extended time, if needed without fear of distortion.

2- Concentrated slurry solution mixed wit Hydrocal, it is produces a hard and
accurate record. The mix of the material is free flowing and yet will set rapidly.
The record can be kept for an indefinite period without fear of distortion.

3- Modeling plastic, it is hardly a pressure-free material and the accuracy of the
record should be verified. Once chilled, the record is hard, but it still susceptible
to distortion. It should be used to mount the casts immediately.

4- Baseplate wax it is difficult to soften it evenly to obtain an accurate record.
Waxes that contain metallic particles (such as Aluwax) can be uniform, Softened,
but even after this type of wax is chilled' remains pliable and can be distorted.

d- Clinical Procedures

The framework with the record base and occlusion rim attached is tried in the
patient's mouth. The height of the occlusion rims must be adjusted so that no
contact takes place between the opposing teeth and the rim. A space of
approximately 1 mm is desired.

   When the opposing occlusion rims are to be used. The mandibular rim is
usual used to establish the ideal occlusal plane because the landmarks that are
normally present. The posterior height of the rim is established at 2\3 the height
of the retromolar pad and anterior to the height of the remaining teeth.

   If opposing occlusion rims are to be used, the recording medium is normally
placed on the mandibular rim. The maxillary rim should be indexed with several
V-shaped notches. A separating medium, petrolatum, should also be used over
the surface of the maxillary rim.



                                                                     Mostafa Fayad 11
                                                      Establishing occlusal relationship


    The surface of the occlusion rim that is to support the recording medium
should be roughened. To ensure that the record will remain attached to it.

    If the record is made at C R position, the patient's mandible should be guide
to the most retruded position& allowed to close. If the CO position is to be used,
the patient should close in that position.

The greatest cause of incorrect jaw relation records is pressure. If any force
occurs on the occlusion rims, the distal extension record base will depress the
soft tissue beneath the base. This is enough to cause an incorrect jaw relation
record.

If the jaw relation record is accurate, the casts may be mounted on the articulator
and the artificial teeth selected and set.

4- Occlusal relations using occlusion rims on record bases

  It is used when

    one or more distal extension areas are present,

    when a tooth-supported edentulous space is large,

    when opposing teeth do not meet.

- Occlusion rims on accurate jaw relation record bases must be used.

- Visible light-cured (VLC) or autopolymerizing acrylic resin, cast metal,
compression molded or processed acrylic resin bases can be used to made a
record bases for jaw relation records.

- The recording proceedes much the same as in the previous method, except that
occlusion rims are substituted for remaining teeth.

    Jaw relation record bases are useless unless they are made on the same cast
or a duplicate cast on which the denture will be processed, or are themselves the
final denture bases. The latter may be either of cast alloy or a processed acrylic
resin base.

                                                                       Mostafa Fayad 12
                                                    Establishing occlusal relationship


Methods for recording centric relation on record bases:-

        There are many ways by which centric relation may be recorded when
record bases are used. The least accurate is the use of softened wax occlusion
rims.

Modeling plastic occlusion rims, on the other hand, may be uniformly softened
by flaming and tempering, resulting in a generally acceptable occlusal record.
This method is time proved, and when competently done, it is equal in accuracy
to any other method.

- Modeling plastic occlusion rims, are uniformly softened by flaming and
tempering, resulting in a generally acceptable occlusal record.

- When wax occlusion rims are used, they should be reduced in height until just
out of occlusal contact at the desired vertical dimension of occlusion. A single
stop is then added to maintain their terminal position while a jaw relation record
is made in some uniformly soft material, which sets to a hard state. Quick-setting
impression plaster, bite registration paste, or autopolymerizing resin may be
used.

- With any of these materials, opposing teeth must be lubricated to facilitate easy
separation.

- When two blocks are being used, one of the bite blocks is inserted first and the
occlusal plane is trimmed to the correct level. Which block is selected depends
upon which arch will be the greater help in aligining the occlusal plane. If a
posterior molar is standing the plane is adjusted to a level indicated by this tooth.
If no posterior teeth are present (Kennedy class I & II ), the lower occlusal plane
should be trimmed first to a level indicated anteriorly by the abutment teeth, and
posteriorly by the center of the retromolar pad.

- The upper block is then inserted and the occlusal plane is trimmed to provide
even contact with the lower at the predetermined occlusal vertical dimension.




                                                                     Mostafa Fayad 13
                                                    Establishing occlusal relationship


5- Jaw relation records made entirely on occlusion rims

       It is used when

            no occlusal contact exists between the
              remaining natural teeth, such as when an
              opposing maxillary complete denture is to
              be made concurrently with a mandibular
              partial denture.

            used in those rare situations in which the few remaining teeth do
              not occlude and will not influence eccentric jaw movements.

            Jaw relation records are made entirely on occlusion rims when
              either arch has only anterior teeth present.

   In any of these situations, jaw relation records are made entirely on occlusion
rims. The occlusion rims must be supported by accurate jaw relation record
bases. Here the choice of method for recording jaw relations is much the same as
that for complete dentures. Either some direct interocclusal method or a stylus
tracing may be used.

       As with complete denture fabrication the use of a face-bow, the choice of
articulator used, the choice of method for recording jaw relations, and the use of
eccentric positional records are optional according to the training, ability, and
desires of the individual dentist.




In this case recording jaw relations is such the same as that for complete
dentures. This includes:

   1- Establishing proper facial contour, and orientation of the occlusal plane.

   2- Determination of vertical dimension of occlusion.

   3- Mounting the upper cast according to a face-bow record.

                                                                     Mostafa Fayad 14
                                                   Establishing occlusal relationship


   4- Registration of centric relation,

   5- Locking the maxillary and mandibular occlusion blocks and mounting the
       lower cast on articulator.

   6- Registration of eccentric jaw-relations.

II -Functionally Generated Path Technique
   Clinical Procedure :         An acrylic resin denture base is
attached to the framework. A specially compounded hard wax
occlusion rim is constructed on the acrylic resin base. This
occlusion rim is constructed slightly high in occlusal contacts
and will keep the remaining natural teeth apart from 0.5 to 0.7mm. The extra
height is necessary to develop the full range of motion. The occlusion rim should
be made several millimeters wider than the buccolingual width of the tooth
opposing the rim.        There are two methods of having the patient grind the
occlusal pathways.

The first method:-

     The patient take the framework with the denture base and occlusion rim
attached home and to wear it continuously for 24 hour except when eating and
when drinking hot or chilled drinks.

     The patient who wears the prosthesis overnight must be reminded to
intermittently close the jaws together firmly and to grind against the wax in all
possible jaw position.

     The value of the patient's wearing the denture while sleeping is that
involuntary or bruxing contacts will be recorded. The resulting pathway will be a
record of all possible jaw movements and tooth contacts even though some of the
contacts may be undesirable.

      The completed wax pattern will resemble a slightly larger version,
buccolingually, of the teeth that originally occupied the edentulous space.

                                                                    Mostafa Fayad 15
                                                   Establishing occlusal relationship


    This wax pattern is boxed and poured in improved dental stone to provide a
permanent record of the generated pathways. The stone record is mounted on an
articulator.

      The second method:-

   The patient is creating the pathway in the dental office directly under the
supervision of the dentist.

   Advantage of this method: - the dentist's being able to observe and correct the
movement the patient is making.

Disadvantage of this method: - normally a patient will require at least 30
minutes of active movement to complete a pathway.

  The record should be removed and examined every few minutes. The wax will
exhibit a glossy surface where tooth-wax contact is occurring. Those areas not in
contact will appear dull. Wax may be melted and added to those areas to ensure
complete and even contact. The record is boxed and poured the same as for the
overnight record.

Artificial Teeth Set to the Generated Path

   1- The incisal guide pin is opened 1 mm before the artificial teeth are
       positioned. This increase in vertical dimension will be returned to normal
       by selectively grinding the denture teeth. The selective grinding also
       develops the occlusal anatomy of the denture tooth to conform to the
       functionally generated stone path.

   2- The denture teeth are positioned over the framework in the correct
       anteroposterior and buccolingual position. Then the incisal guide pin is
       returned to correct vertical dimension of occlusion.

   3- A water-soluble Prussian blue dye is painted on the surface of the
       generated path. The articulator is locked in C R, and opening and closing
       tapping movements are made of the stone path against the denture teeth.


                                                                    Mostafa Fayad 16
                                                      Establishing occlusal relationship


   4- The spots of dye transferred from the stone pathway to the denture teeth
        indicate the areas of contact and are reduced by grinding.

   5- Selective grinding is continued until the incisal pin again contacts the
        incisal table.

     At this time, intimate contact should be present between the artificial teeth
and the stone pathway. The articulator is not moved into protrusive and lateral
excursions because these positions are incorporated in the pathway.

Advantages:-

   1-    Eliminates the need for adjusting an articulator with interocclusal record
         or a tracing device.

   2-     Eliminates the need to make a face-bow transfer, because all the in-
         formation derived from a face-bow transfer is contained in the pathway.

There are limitations or disadvantages to the use of the generated path.

   1-      If opposing partial dentures are required, one of the partial dentures
           must be completed before the other can be made by the articulator
           method and then to functionally generate a pathway for the complete
           denture.

   2-      Can not used in distal extension R P D because during the generation
           of the path in the hard inlay wax, movement of a distal extension base
           carrying the occlusion rim is possible. This will produce an inaccurate
           pattern that will appear to be complete.

   3-       Verification of a recording in the mouth is difficult.

Numerous studies have also shown that the masticatory cycle differs depending
on the type and texture of food being chewed. This may mean that the pattern
developed in the wax is accurate for the wax only and that food-stuffs may fall
inside or outside the particular chewing cycle.



                                                                       Mostafa Fayad 17
                                                    Establishing occlusal relationship


ESTABLISHIN         JAW      RELATION        FOR     A    MANDIBULAR              RPD
OPPOSING A MAXILLARY CD :

 (1) If mandibular removable partial denture occluding with maxillary
complete denture-

  - If existing denture is satisfactory and occusal plane is oriented to an
acceptable anatomic, function and esthetics position than complete denture not
need to b replaced and treated as a intact arch.

 - A face bow transfer is made of that arch and cast is articulated on the
articulator.

  - than face bow and complete denture is remover and irreversible hydrocolloid
impression of the denture is made.

 - A cast is formed from the impression and mount on the articulator.

 - Than centric relation recorded and transferred to the articulator.

(2) When the removable partial denture replaces all posterior teeth and the
anterior teeth are no interfering.

 A central bearing point tracer is used may be mounted im the plate on maxillary
denture. A centric relation are recorded by means of introral stylus tracing
against the stable mandibular base.

When a existing complete denture opposing a arch on which removable partial
denture is fabricated. A cast of complete denture is used during the fabrication
procedure.

(3) If the mandibular removable partial dentures is tooth supported than
mandibular arch resorted first.

In other instance the mandibular arch is restored first and jaw relation are
established if they would be a full complement of opposing teeth. Thus the
maxillary complete denture is occluded with an intact arch.


                                                                        Mostafa Fayad 18
                                                      Establishing occlusal relationship


Establishing appropriate functional balanced occlusion of
partial denture:

   In designing occlusion for partial dentures, the location of the edentulous area
and the condition of the opposing arch will significantly influence the desirable
occlusal contacts during functional movement of the mandible.

   The objective of creating occlusal contacts during escursive movements of the
mandible is to broadly distribute forces over the supporting structure and to
reduce tipping of the removable partial denture. Simultaneous bilateral contacts
of the opposing posterior teeth must occur in the selected horizontal jaw position
in all cases.

   1- For Kennedy class I mandibular partial denture, opposing completely
        edentulous maxilla. Balanced occlusion (working balancing and
        protrusive contacts of the posterior teeth, with light contact of the
        anterior   teeth ) should be formulated to promote stability of the
        maxillary denture.

   2- When maxillary Kennedy class I removable partial denture opposing
        mandibular class I partial denture working and balancing sides contact
        should be formulated to minimize tipping of maxillary partial denture
        and broadly distribute the forces. Such arrangement will compensate in
        part for the unfavorable position of the maxillary artificial teeth to the
        crest of the ridge, which is usually lateral to the crest of the ridge.

   3- For mandibular class I partial denture opposed by natural dentition.
        Simultaneous, working side contact only should be formulated.

   4- For Kennedy class II mandibular, or maxillary partial dentures only
        working side contacts should be formulated.

   5- For class IV maxillary removable partial denture, opposing natural
        dentition, contact of the opposing anterior teeth in centric occlusion is
        desirable to prevent a continuous eruption of the mandibular incisors.

                                                                       Mostafa Fayad 19
                                                    Establishing occlusal relationship


        Contact of the opposing teeth in eccentric position should be avoided to
        prevent overloading of maxillary arch and the formation of flabby tissue.

   6- For Kennedy class III partial denture, opposing natural dentition contact
        of the posterior teeth during functional movement is not desirable, since
        stability of the denture is maintained by direct retainers on both sides.

Guidelines for the choice of partially edentulous patients occlusal concept.

Maxillary arch              Mandibular arch             Occlusal scheme

Fully           edentulous Kennedyt         class    I Balanced occlusion working
restored by C.D.            restored by R.P.D.          balancing protrusive.



Kennedy class I restored Kennedy class I                Working side contact
by R.P.D.
                            restored by R.P.D.



Fully dentate
                            Fully dentate               Working and balancing side
                                                        contact

Kennedy class II                                        Working side contact
                            Fully dentate



Fully denture                                           Working side contact
                            Kennedy class II



Class III                                               Working side contact
                            Class III



Class IV                                                Contact in centric no-eccentric
                            Fully dentate
                                                        contact



                                                                     Mostafa Fayad 20
                                                                      Try-in of RPD


                           TRY IN OF RPD
       Even the best partial denture frameworks do not fit perfectly in the mouth.
Stewart Rudd and Kuebker have stated that up to 75% of all frameworks may not
fit the mouth on the day of insertion. Since clasp tips are designed to fit passively
into a specified undercut, any discrepancy in seating of the partial denture
framework will cause the direct retainers to become active, thereby causing
orthodontic movement of the teeth. For this reason, frameworks must be adjusted
intraorally.

This stage of treatment may require action in two phases:

1. Trial of a cast metal framework, where one is included in the design of a partial
denture.

2. Trial of the partial denture, with the replacement teeth arranged on a temporary
or 'permanent' (metal) baseplate.




                                    Mostafa fayad                                 1
                                                                  Try-in of RPD


                    Framework Evaluation
A] Extraoral evaluation of the Framework

a- Check the framework on the master cast

    Design drawn on the diagnostic cast was followed

    Location of the components

    Fit of the framework on the master cast

    Amount of undercut and Soft tissue relief

    Inspect the rests.

    Examine the relationship between the framework and the soft tissue areas.

    Check for proper adaptation and placement of clasps:

    Check for proper adaptation and placement of the lingual plate:

    Check the ease of framework removal

b. Inspect the framework off the master cast:

    Cheek for abraded areas of the master cast:

    Partial denture component

    The finishing and polishing of the framework:

    Presence of defects

    Finish lines

c. Radiographic evaluation




                                  Mostafa fayad                              2
                                                                       Try-in of RPD


B] Intraoral evaluation of the Framework

1-Seating the framework (Checking fit):

(a) Fitting the framework to the abutment teeth,

        i. Seat the framework in place carefully with minimal force:

        ii. Check for rocking of the framework in both anteroposterior and
        buccolingual direction:

        iii. Check for close adaptation of rests, clasp arms, and lingual plates:

        iv. Cheek for physiologic relief on distal extension frameworks:

(b) Fitting the framework to the soft tissue (Check soft tissue contact or relief):

(c) Adjusting the framework to the opposing occlusion.

2- Checking for clicking or tilting during insertion

3- Verifying retention and reciprocation:

4- Checking stability

5 – Checking for deformed clasp :

6- Checking aesthetics

7- Checking occlusion:

8- Finishing and polishing ground surfaces :




                                     Mostafa fayad                                    3
                                                                        Try-in of RPD


A] Extraoral evaluation of the Framework (Pre-clinical Inspection
and Adjustment)

For examination of the completed laboratory work , Careful inspection should be
accomplished using magnification, the following should be observed:

a- Check the framework on the master cast

1-If the design drawn on the diagnostic cast was followed. The dental laboratory
should never change the framework design without consulting the dentist.
Conversely, errors in framework design caused by inaccurate drawing on casts or
omissions in laboratory prescriptions are the fault of the dentist.

2-     Location of the components. The position of the framework components
should correspond to the design indicated on the master cast.

3.     Fit of the framework on the master cast.

The fit of the framework to the master cast. The framework should fit the master
cast. If it does not, it will probably not fit intraorally. Replace the framework on
master cast as little as possible to prevent abrasion (in case a remake is necessary).

       a.      Complete and stable seating. The framework should demonstrate
       accurate adaptation of the rests to their rest seats without rebound.

       b.      Adaptation. Confirm intimate adaptation of the framework to the
       master cast, where indicated.

       c.      Relief. Confirm areas of relief between the framework and master
       cast, where indicated.

4. Evaluate the amount of undercut and Soft tissue relief.

5. Inspect the rests.



                                       Mostafa fayad                                   4
                                                                     Try-in of RPD


     Check to see whether the rests are fully seated: The margins of the rests
     should be flush with the margins of the rest seats. If they are not, the source
     of interference should be determined and corrected.

     Evaluate the contours of the rests: overcontoured rests will interfere with
     occlusion, and undercontoured rests may be too thin and weak and subject to
     fracture.

6. Examine the relationship between the framework and the soft tissue areas.

       Inspect areas where the major connector is in contact with soft tissue,and
make sure there is intimate contact to prevent food from getting beneath the
framework.

       Make sure there is adequate gingival exposure around minor connectors
and approach arms for bar-type clasp assemblies. There should be 5 mm between
minor connectors and other vertical components. Horizontal portions of I-bars
should be 3 mm from the gingival margin, and the vertical portion should be 5 mm
from other vertical components.

       Check relief under bar clasps and acrylic resin retentive mesh, and make
sure the tissue stop rests on the crest of the edentulous ridge.

7. Check for proper adaptation and placement of clasps:

       Clasp arms, guide planes, and reciprocating arms should be in intimate
contact with the tooth structure. Gaps left between clasps and tooth structure will
allow food to collect between the framework and the teeth, which may result in
decalcification, caries, and gingival inflammation.

       Clasp arms should have the proper shape, diameter, and taper. Wrought
wire clasps should be long enough and the solder joint placed far enough away
from the tip to allow adequate flexibility.


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                                                                      Try-in of RPD


8. Check for proper adaptation and placement of the lingual plate:

       When properly designed and constructed, the lingual plate will be scallop
shaped to close off the interproximal embrasures and cover the cingulum areas.
Open spaces between the lingual plate and the teeth can result in food impaction
and gingival inflammation, which may lead to bone loss in the area. A space may
also encourage the patient's tongue to play with the edge of the framework.

9. Check the ease of framework removal:

In fact retention may be greater on the cast because of friction and the rough
surface of the cast.

b. Inspect the framework off the master cast:

1- Cheek for abraded areas of the master cast:

The abraded areas on the cast correspond to areas of interference in the mouth.
Areas that necessitate close inspection include rest seats, guide planes, the lingual
surfaces of mandibular bicuspids and molars, retentive areas, and the junction
between minor connectors and clasp arms.

2- Partial denture component: The framework should be assessed using the
following criteria:

    Rest seats should be fully seated (adequate support)

    Reciprocal arms and proximal plates should be contacting the cast

    Linguoplates and maxillary palatal major connectors should be in intimate
       contact with the cast (food impaction)

    Major and minor connectors should be an adequate distance from abutment
       teeth (hygiene). Adjust, if possible, or have lab adjust or remake framework



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 Major and minor connectors should be of proper proportions (rigidity,
   hygiene).
 The rigidity of the major connector should be tested with finger pressure

Note especially that cingulum rests should not be carried into embrasures and
that embrasure minor connectors for distal extensions should not be in contact
with the more anterior tooth (unless it has a rest seat preparation). Adjust, if
possible, or have lab adjust or remake framework.

 Butt joints should be adequate for acrylic resin (slightly undercut). Adjust,
   if possible, or have lab adjust or remake framework

 Proper gridwork should have adequate relief

 Thickness of the components. The dimensions of the
   framework components should be evaluated to ensure
   that they are appropriate for the required mechanical
   properties.

        o a.     Major connectors. The major connector should demonstrate
           dimensions which provide rigidity and strength.

        o b.     Rest - minor connector j unction. A minimum metal thickness
           of 1.5 mm at the junction of the rest with the minor connector is
           required for base metal alloys (2 mm for gold alloys).

        o c.     Clasp taper. Retentive clasps should taper uniformly in
           thickness and width. Bracing clasps should possess dimensions
           which provide rigidity and need not be tapered.




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3- The finishing and polishing of the framework:

     Finish and polish of the framework should be adequate - no evidence of
pits, nodules and scratches in the metal. Eliminate sharp edges that might impinge
on the oral mucosa.

        a- Inner surfaces of the framework should be free from pits , scratches and
        bubbles .

        b- The framework should be highly polished , except the fitting surface
        the fitting surface of the maxillary major connector should be lightly
        polished .

        c - Both internal and external finish lines should be sharp , definite and
        slightly undercut .

         d- The taper of the clasp should be uniform and free from nicks and
        notches.

4- Presence of defects. The framework should be evaluated for defects that might
compromise its adaptation or strength.

        a.   Positive bubbles or blebs. May inhibit complete seating of the
        framework on abutment teeth or traumatize soft tissue.

        b.   Voids or porosities. May weaken the framework and lead to fracture.

5-    Finish lines.

        a.   Staggered (offset) finish lines. In order to maintain framework
        strength, the internal and external finish lines should not be superimposed.

        b.   The internal line angles of external and internal finish lines should
        be less than 90 degrees to provide mechanical retention for the denture
        base resin.


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C - Radiographic evaluation; it shows the invisible porosity and the size of the
partially visible one.

1. Porosity not visually detectable. Radiographs may demonstrate internal
porosity.

2.     Porosity visually detectable. Radiographs may indicate the size of a
porosity which is only partially visible.

3.     Technique.

            a.   10 MA - 100 KVP - 15/60 seconds.

            b. 15 MA - 70 KVP -15/60 seconds.

B] Intraoral evaluation of the Framework

1-Seating the framework (Checking fit):

       The framework should be positioned correctly over the standing natural
teeth and gentle seating pressure applied along the path of insertion selected when
the study cast was surveyed. It should be found to slide easily into the fully seated
position, only moderate resistance being encountered corresponding to the
retentive value of any clasps which are present. If any undue resistance to
movement is encountered in the seating process,

       Excessive force should not be applied as this may cause discomfort or make
it difficult to remove the framework subsequently without overstressing the
periodontal attachment of the tooth.

       A near fit of the framework is not sufficient; an accurate fit is essential for
success. The framework may fit the cast but does not fit in the mouth, due to:

                   A distorted impression,



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                An improperly poured cast,

                An abraded cast, and/or

                Shifting teeth.

      In the latter two instances, if the interferences are minor and can be located,
one may be able to, with care, adjust the framework into place.

      One should avoid over reducing contacts on guide planes, rests, and
retentive tips. Contacts between the framework and the teeth gingival to the survey
line should not be arbitrarily removed, because these contacts can help guide the
framework into place and provide some degree of retention and stability.

      The most common areas that interfere with seating are:

             1.     under rests

             2.     rigid portions of direct retainers (e.g. above the survey line)

             3.     interproximal portions oflinguoplate major connectors

             4.     interproximal minor connectors

             5.     shoulder areas of embrasure clasps

      To locate small areas of the framework that are interfering with the fit,

      a) By visual and tactile examination, an attempt should be made to
determine where resistance to further movement is occurring. Location of the
exact site of resistance can be assisted by the use of the disclosing wax. The
resistance area will be revealed as the area where the wax has thinned to display
the underlying metal.

      b) A probe may also be used to check the closeness of fit of any elements
contacting the teeth. Clasp arms should be checked for non traumatic placement


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relative to the gingival margins of the teeth. The various component elements
should also be checked for correct positioning relative to the soft tissues. For
example, gingivally approaching clasp arms should not enter soft tissue
undercuts. Palatal connectors on an upper framework should be in contact with the
underlying tissues. Where a lingual bar has been used in the design of a lower
framework, it should be correctly positioned relative to the gingival margins of the
standing teeth and the functional level of the lingual sulcus.

       c) The patient should be questioned as to whether or not they feel any
discomfort when the framework has been inserted. Where the patient can detect a
pressure area, particularly in relation to covered soft tissues, it may be necessary to
relieve pressure in the area concerned by grinding the fitting surface of the
framework.

       d) Some type of disclosing medium is needed. See later




The fitting of the framework to the mouth should be done in three phases:

       (a) Fitting the framework to the abutment teeth,

       (b) Fitting the framework to the soft tissue, and

       (c) Adjusting the framework to the opposing occlusion.

a. Fit the framework to the abutment teeth:

i. Seat the framework in place carefully with minimal force:

Use gentle pressure over the rests as the framework is seated along the path of
insertion. Areas of interference must be relieved.

The most common areas that will interfere are: the junction between rests and
minor connectors, periphery of rests, guide planes, undercut areas, and clasp arms.


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Failure to relieve even the smallest amount of interference can cause slight but
continuous pressure on abutment teeth, which may cause pain and discomfort.

Repeat the adjustment steps until the framework is seated in place uniformly and
completely.

ii. Check for rocking of the framework in both anteroposterior and
buccolingual direction:

Place fingers on the rests and rock the framework. The rests should stay in place
and not lift out of the rest seats as pressure is applied to one side and then the
other.

iii. Check for close adaptation of rests, clasp arms, and lingual plates:

         After the framework has been seated, it is evaluated for fit . All rests should
seat completely in their prepared seats. Clasps, indirect retainers and minor
connectors should be in intimate contact with the abutment teeth. The adaptation
of the framework to the teeth may be confirmed by rouge and chloroform or
disclosing wax.

A sharp explorer is the instrument of choice to determine whether margins are
open or closed.

         Excess saliva and bubbles should be blown of the teeth. All metal structures
designed to contact tooth structure should be adapted closely to the teeth, which
will ensure a precise fit.

iv. Cheek for physiologic relief on distal extension frameworks:

Place pressure on the retentive meshwork areas and observe:

 The movement of the clasp arms and guide planes.




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 Disengagement of the retentive tips and guide planes as the framework rotates
around the rest seats.

 Proximal contact areas between abutments and adjacent teeth to ensure that the
abutments are not being torqued during rotation of the framework. Make sure
there is enough clearance between the proximal plate and gingiva to allow some
movement of the framework without tissue impingement.

Care should be taken when the framework is adjusted along the occlusal edge of
guide planes, rests, and major connectors. Do not accidentally open the
tooth/metal contact and create an area for food impaction.

b. Fitting the framework to the soft tissue (Check soft tissue contact or relief):

       Make sure there is adequate space between the meshwork and the soft
tissue to allow a sufficient amount of acrylic resin material under the retentive
meshwork.

       The tissue stop must be in contact with the edentulous ridge. The retentive
arm of a bar-type clasp should not impinge on soft tissue. There should not be an
excessive amount of relief that could result in a food trap.

       The same can be said for minor connectors that cross soft tissue. Lingual
plates or bars should not impinge on soft tissue in the lingual vestibule area.

Additional relief may be necessary if tori are present.

c. Adjusting the framework to the opposing occlusion: see checking occlusion




2- Checking for clicking or tilting during insertion:




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A – There should be no clicking during insertion , which occurs when a rigid
portion of the framework is being forced into an undercut .

B- Tilting during seating from the intended path of insertion , results when clasp
arm in one side is more rigid or extended into a deeper undercut than the other side
. To equalize force during seating and prevent tilting , the resisting clasp is
reduced in diameter , or its taper is increased .

3- Verifying retention and reciprocation:

         The resistance by the framework to vertical dislodging force should be
evaluated. While seating and removing the framework slowly, the relationship
between the clasp arms and the abutments is observed.

After the framework is properly seated, remove and replace the framework several
times to evaluate retention. If there is too little or too much retention, the clasps
can be carefully adjusted.

The instruments of choice are orthodontic contouring pliers, which have smooth
beaks.

After adjustment, the clasp should have the desired retention and still be intimately
adapted to the tooth surface.

Avoid over bending the clasps, which may change the characteristics of the metal
through work hardening.

         An over retentive framework can be detected by a snap or click as the
framework seats. The clasp should be in passive contact with the tooth when the
framework is completely seated. With over retentive clasps, tipping forces will
cause a destructive effect on the periodontal support tissues.




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       The amount of retention can be reduced by adjusting the clasp to engage a
smaller amount of undercut or by reducing the degree of adaptation to the tooth
surface.

As long as the forces are limited and do not exceed the elasticity of the periodontal
fibers, there should not be any damage to the teeth.

       Each reciprocal arm should contact the abutment just prior, or at the same
time as the retentive arm. This will brace the abutment against the force applied by
the flexible retentive arm.

4- Checking stability

       Stability of the framework should be checked by applying pressure on
various elements - rests, saddles and palatal connectors in particular – and noting
whether any rotational displacement occurs.

       Special attention is necessary when checking the stability of a framework
carrying one or two free-end saddles. It is usual for the free-end saddle portion of
a metal framework to have been relieved from tissue contact in the constructional
procedure, to enable the saddle to be relined where this is subsequently required.
Before testing the stability of the free-end saddle element of a metal framework
which has been relieved from tissue contact, it is advisable that a wax baseplate be
positioned to bridge the gap between the metalwork and the underlying tissues.

       Where the design of the partial denture includes the use of a stress-
breaker, especially where this is of Type 1, an appreciable degree of rotational
displacement should be observable when pressure is applied to the metalwork of
the free-end saddle. Where no stress breaker has been used, and yet an appreciable
degree of rotational displacement of the free-end saddle occurs when this check is
applied, there is a need for subsequent action to be taken to overcome this




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instability. This will usually involve relining of the free-end saddle at the insertion
stage of treatment.

5 – Checking for deformed clasp :

       A clasp may have been deformed during finishing and polishing . A clasp
under tension may force the frame to assume wrong or tilted position . This
condition is mostly seen with wrought wire clasps . Deformed clasp should be
corrected and should be passive when fully seated .

6- Checking aesthetics

       The framework should be inserted and its appearance noted when the
patients lips are at rest and when the patient is smiling. If any elements of the
metalwork are visible when the patient smiles, it is advisable to point this out to
the patient and show them what is involved with the aid of a hand mirror.

       If proper care has been applied in the stages of treatment planning and
denture design, objections to the aesthetics of a metal framework should be rarely
encountered. Where objections do arise, they usually relate to an unaesthetic
display of clasp arms or incisal rests. Where this is due to an unnecessary
thickening having occured in the construction of the framework, it may be
possible to overcome the objections by reducing the thickness of the element
concerned by grinding.

7- Checking occlusion:

       Vertical dimension should remain unchanged by a removable partial
denture in almost all instances. The framework should not interfere with normal
centric and eccentric contacts

       If both maxillary and mandibular frameworks are being constructed, only
one at a time should be corrected. Then, they should be tried in the mouth


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together. Any interference noted now will be between the metal of the opposing
frameworks.

       The patient should be guided into centric, protrusive and lateral
positions, with articulating paper is placed over the teeth, to locate the interference
in these positions. Mark occlusal contacts with thin articulating paper and remove
the framework for adjustment.

       The highly polished metal surfaces do not mark well with articulating
paper so that the opposing occlusion should be checked for heavy contacts.
Diamond burs, heatless stones, Shofucoral stones or cross cut Brasseler lab burs
will most readily remove interferences. DO NOT FORGET TO LOCATE AND
ADJUST EXCURSNE INTERFERENCES.

       Heatless stones or diamond instruments in the high speed hand piece are
used to reduce the interference, first in centric occlusion, then eccentric positions.

       The framework must not keep the natural teeth from making normal
occlusal contact in either centric or eccentric closures. Since most frameworks are
be fabricated on unmounted casts there are usually occlusal interferences present
on rests and indirect retainers. These should be adjusted at this time.

-- Occlusal rests or indirect retainers that have inadequate thickness ( 1.5
mm) after adjustment will be subject to fatigue and possible fracture.

       The inadequate thickness may occur due to inadequate preparation (i.e.
not considering opposing occlusion) or subsequent extrusion of teeth. If the teeth
have extruded, the entire framework will most likely not fit.

       If occlusal interferences exist that will excessively thin the rests, the rest
seat preparation may have to be deepened and a new impression taken, or an
opposing cusp or framework



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                                                                     Try-in of RPD


       element may have to be reduced. Reduction of opposing cusps should be
performed as a last resort to save an otherwise acceptable framework.

-- Occlusal interferences should not normally occur on    retentive clasp arms
if proper treatment planning has been followed. However, if the opposing
occlusion is not considered at the time of mouth preparations, it is possible that
occlusal contact may occur on a retentive arm. If this contact is minor, the
opposing cusp may be reduced. Again, reduction of opposing cusps should be
performed as a last resort to save an otherwise acceptable framework. If the
interference is gross, the tooth surface should be recontoured (i.e. lower height of
contour) and a new impression taken. IN NO INSTANCE SHOULD A
RETENTIVE ARM BE RELIEVED, since this will affect its flexibility and
resistance to fracture.

       When occlusal discrepancies framework are corrected, care must be used
not to cut excessively and thus weaken the occlusal rests or clasp arms . If the
occlusal clearance is insufficient , in preference to weakening the framework by
too much metal reduction , the opposing tooth may be relieved to obtain the
necessary clearance .

       Where the natural dentition does not contact at the required occlusal
vertical dimension and the design of the framework includes onlays, a check
should be made that with the framework inserted the opposing natural teeth and
the metalwork contact evenly at a vertical dimension providing an acceptable
freeway space.

       Adjusting the framework to the opposing occlusion:

       i. Identify natural tooth contacts in the centric occlusion (C0) or
maximum intercuspation positions (MIP):




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                                                                    Try-in of RPD


       The framework should not prevent the natural dentition from contacting in
the CO/MIP or during normal functional movements.

       Start by removing the framework, and identify CO/MIP and eccentric
contacts between the natural dentition. These contacts will be the reference points
for judging the amount of occlusal adjustment needed.

       ii. Adjust the framework in the C0 /MIP position:

        Place the framework in the mouth, and determine whether the-natural
dentition is able to reproduce the CO/MIP contacts. If not adjust the framework
until the teeth reproduce the desired occlusal contacts.

        Roughen up the surface by sandblasting with aluminum oxide or lightly
grinding with a fine carborundum stone, since highly polished framework metal
does not mark well with articulating paper.

        Place two articulating paper strips simultaneously on both sides of the
mouth, and have the patient close into the Co/MIP position. Two strips are
necessary because patients will tend to bite to one side it only one strip of
articulating paper is used.

        Adjust the framework without over thinning and weakening the metal
components. Rests and clasp arms are usually at risk of being excessively adjusted
and subsequently weakened. However, sometimes tooth migration can reduce the
desired occlusal clearance.

        If there is a risk that, the metal framework might be weakened,
adjustment of the opposing natural teeth may be necessary. Avoid exposing
dentin, and polish and fluoridate the teeth after the adjustment.

       iii. Adjust the framework during eccentric movements:




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                                                                       Try-in of RPD


       During mandibular eccentric movements the patient should reproduce
movements representative of normal masticatory function and not wide excursions
into lateral and protrusive positions. Instruct the patient to use relatively moderate
to heavy biting force.

       iv. Occlusal adjustment of two frameworks:

       If there are two frameworks, adjust the occlusion of each framework
independently.

       Once each framework is in occlusal harmony with the opposing natural
dentition, place both frameworks in the mouth and adjust the frameworks to
occlude with each other.

       Any interference detected should be between frameworks. If adjustment
procedures are carried out correctly, the patient's occlusion should be the same
with and without the frameworks in the mouth.

8- Finishing and polishing ground surfaces :

       After the framework has been fit and occlusal adjustments have been made,
the surfaces of the ground metal must be finished and polished. Carborundum
points and wheels are used to restore smooth finish to all ground surfaces.

       Dedco green knife edge wheels for chrome cobalt alloys will remove
scratches and bring the adjusted surface to a high shine quickly. Additionally,
Dedco blue clasp polishers or any other carborundum impregnated points can be
used to finish the chrome cobalt alloy. A final polish can be placed using a tripoli
on a bristle brush and rouge on a small diameter cloth wheel. Use care not to snag
the cloth wheel on sharp edges of the framework (to prevent injury to yourself).
Remove traces of the polishing compounds with soap and water and a toothbrush.

       Adjusting and polishing tools:


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                                                                     Try-in of RPD


       The framework can be adjusted with various burs, coarse Carborundum
stones, or both. All adjusted areas should be repolished with rubber points and
wheels.

       For final polishing use a rag wheel and polishing compound.

       When relieving or polishing, avoid staying in one spot for extended periods
of time to prevent the generation of localized areas of high temperature, which can
run the risk of changing the temper of the framework metal.

Special Adjustments for Distal Extension Cases:

       In most cases distal extension cases will be designed with relatively short
occluso-gingival guiding planes to allow for release of the abutments during
tissueward movement of the denture base. However, there are some cases where
teeth are tipped and a long guiding plane is the only type of guiding plane that can
be placed. In these instances, "physiologic relief' of the framework should be used
to provide release. With this technique the distal guiding planes, minor connectors
and linguoplates are coated with alcohol and rouge (not wax or silicone). The
framework is placed intraorally and placed under hyperfunction by pressing over
the distal extension gridwork. The framework is removed and the guideplanes and
other rigid metal contacts, which could torque the tooth, are relieved in areas of
burn-through. Relief should be provided so that marks remain in only the occlusal
one third of the guiding planes.

       It should be noted that it is inadvisable to attempt to rectify any faults
which are present in a framework (for example, inadequate retention in clasp
arms) by bending the framework. It is virtually impossible to apply bending
without disrupting the essential passive placement of the elements relative to the
oral tissues. A bent framework may well give rise to appreciable tissue damage.

.


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                                                                        Try-in of RPD




       TRIAL PARTIAL DENTURE BASE TRY-IN

Indications:

   A. Evaluation of Esthetic, and phonetic characteristics of the prosthesis. If
      anterior teeth are being replaced, an esthetic try-in is essential.

   B. Evaluation of the accuracy of the jaw relationship when all posterior teeth
      in one or both arches are being replaced.




EXTRAORAL EXAMINATION:

Each denture should first be examined on the articulated casts.

INTRAORAL EXAMINATION

   A. Checking extension, retention and stability: as in complete denture

   B.Esthetic try-in:

      • It is better if the dentist examines the teeth in the mouth before the patient
      has an opportunity to observe them. Corrections can be made without
      upsetting the mental attitude of the patient.

      • Attention should be given to:

            a) The anteroposterior position of the anterior teeth for adequate lip
            support. Evaluate the positions of anterior teeth and assess lip support.

            b) Tooth length in relation to lip length and length of the remaining
            natural teeth.




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    c) Mesiodistal width of the replacement anterior teeth (decreased or
    increased).

    d) Horizontal and vertical overlap of the anterior teeth.

    e) Vertical alignment of the teeth.

    f) The maxillary first premolar. (Considered anterior tooth in many
    patients)

    g) Shade, size and shape.

    Facial support affected by:

    ! Position of the incisal edge

    ! Thickness and contour of the labial flange

Procedures

  1) The patient should be seated in a quite, relaxed atmosphere. This
     which helps him to alleviate the tension since he views the tooth
     arrangement for the first time.

  2) The denture base should be clean, and resistant to tooth
     displacement.

  3) Carefully insertion of the RPD and tell the patient to avoid
     application of biting forces.

  4) Then the patient is directed to close lightly to ensure that no
     interference is present.

  5) The dentist should evaluate the position of anterior teeth and assess
     lip support.




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                                                                      Try-in of RPD


          6) Tooth length should be carefully evaluated.

          7) If an anterior edentulous space has been decreased by drifting of the
             teeth, decreasing number of teeth should be avoided, instead,
             attempts should be made to rotate or overlap the denture teeth in
             order to give an acceptable esthetic result.

          8) If the anterior edentulous space is relatively large, diastema may be
             incorporated into the tooth arrangement.

          9) Checking of the horizontal and vertical overlap of the anterior teeth.

          10)Examination of the maxillary midline, for its (vertical alignment, and
             for its mid face position).

          11) Checking of the teeth shade specially if there are natural teeth is
             present, which makes shade selection and patient acceptance a
             critical point.

Once the technical and mechanical requirements are satisfied, the patient should
be allowed to view his new RPD and comment on the results. The patient's
remarks should be noted, and required changes should be made.

   1- Abnormal fullness

    If anterior teeth have been missing for 6 months or more, the patient may
      report a sensation of abnormal fullness at the upper lip.

    A short period of accommodation usually will eliminate this problem.

   2-Teeth length

    If all anterior teeth are being replaced and the upper lip is of normal length,
      the edges of the central incisors should be visible when the lip is relaxed.



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                                                                     Try-in of RPD


 When the lip is drawn upward, the gingival contours of the denture base
   should be minimally evident.

3- Short space

 If an anterior edentulous space has been decreased by drifting of the teeth, a
   decreased number of teeth should not be placed.

 Attempts should be made to rotate or overlap the denture teeth in order to
   achieve an acceptable esthetic result.

4-Large space

 If the anterior edentulous space is relatively large, diastemata may be
   incorporated into the tooth arrangement.

 If this is to be accomplished, the patient should be informed of potential
   difficulties associated with interdental spacing.

 Spacing complicates oral hygiene procedures, increases the likelihood of
   food impaction, and may create difficulties with phonetics.

5- Overlap of the anterior teeth.

 If some anterior teeth remain, the overlap should be duplicated.

 If no natural teeth remain, care should be taken to avoid excessive vertical
   overlap without accompanying horizontal overlap.

 This could result in the application of undesirable forces to the artificial
   teeth and associated soft tissues.

6-Vertical alignment of the teeth also should be evaluated.

    A slight deviation from the vertical can produce an acceptable esthetic
      result, but a significant deviation can create esthetic difficulties.

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                                                                  Try-in of RPD


    The practitioner should pay particular attention to the maxillary midline.

    This midline must be examined for its vertical alignment and for its
      midface position.

    Any error in the position of the maxillary midline can be extremely
      distracting.

7- Tooth shade.

    The presence of natural teeth makes shade selection and patient
      acceptance a critical component of removable partial denture therapy.

    To ensure selection of an appropriate shade, the prosthesis should be
      viewed using a variety of light sources.

8- The patient evaluation.

 The patient should stand several feet from a wall mirror to examine the
   teeth critically.

 The use of a hand mirror should be discouraged because the patient’s
   attention will be focused on individual teeth and not on the overall effect of
   the prosthesis.

 The patient’s remarks should be noted, and required changes should be
   made.

 Arrival at mutual acceptance by the patient and dentist frequently demands
   a high level of communicative skill combined with psychological insight.

 Treatment should not proceed until patient approval has been gained.

 Many practitioners insist upon written approval by the patient.




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                                                                        Try-in of RPD


   C. Jaw relation try-in (VERIFICATION OF JAW RELATION) :

 The jaw relation need be verified specially in certain cases:

         1. If doubt exists as to whether the recorded jaw relationship is accurate.

         2. If the partial denture is opposed by complete denture

         3. If all posterior teeth in both arches are being replaced.

         4. If there an: no opposing natural teeth in contact.

 The jaw relation only needs to be verified in limited steps:

             12) Checking of the accuracy of the articulator mounting should be
                performed, especially if problems were present during jaw relation
                procedures.

             13)Evaluation of the vertical dimension is necessary.

             14)Checking the horizontal jaw relationship




In many cases, visual evaluation may be sufficient for checking of the contact of
the opposing natural teeth, and for checking the occlusion in centric and eccentric
positions.




D. Checking phonetics

Maxillary incisors should make fricative “f” and “v” sounds at the wet/dry line of
the lower lip . “s” sound is most important

    Closest speaking space of 1 – 1.5 mm



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                                                                     Try-in of RPD


    Difficult for edentulous patients that have not worn dentures

    Thickness of palate is important

    Arch form must be compatible with Neutral Zone

Whistling usually means too little room for the tongue

Lisping indicates too much room

E. Verification of waxing up

- assess proper shaping and contour of polished surface

- checking peripheral extension

- proper labial fullness

F. patient approval




PRESCRIPTION WRITING

When a trial denture is returned to the laboratory for finishing, the following
information should be provided:

1. The colour and nature of the denture-base material to be used.




                                   Mostafa fayad                               28
                                                                     Try-in of RPD


2. Details of position and depth of anyperipheral seal lines required at the borders
of palatal connectors in an upper denture.

3. Details of any areas which require relief. Information on the site and depth of
relief areas should be given in the written prescription, supplemented by the
mapping out of the required extent of relief areas on the casts. Sites which
frequently require relief include a torus palatinus which is to be covered by an
upper denture base and the gingival areas of standing teeth, where these are to be
covered by connectors.




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                                                                      Try-in of RPD




                            Disclosing media
Ideal requirements of disclosing media

   Easy to apply                           Not require mixing

   Easy to manipulate intraorally          Work will in a wet environment

   Not need time to set                    Shows the degree of interference

   Easy to read                            No potential for false positive results

   Easy to remove from the framework  Not carcinogenic

   Not expensive           Provides 3-D representation of framework adaptation

For effective Use of a disclosing media:

   i. Dry off the framework.

   ii. Apply the disclosing medium,

   iii. Gently seat the framework, and remove.

   iv. Areas that exhibit metal showing through should be adjusted.

   v. The old disclosing medium should be cleaned off.

   vi. New medium applied, and the framework tried in again.

Types of disclosing media

             There are numerous acceptable disclosing media on the market:
             Occlude (Pascal), Accufilm (Parkell), disclosing wax (Kerr/Division
             of Sybron), pressure-indicating paste (Mizzy Inc.), Fit Checker (GC
             Dental Industrial Corp), and chloroform and rouge.

                                   Mostafa fayad                                 30
                                                                           Try-in of RPD




Several media can be used for this purpose:

1.     Rouge and alcohol: A small amount of alcohol
is placed in a dappen dish and a paint brush is wetted
in chloroform and then brushed against the rouge stick
until it picks up the pigment. The pigment is then
brushed in an even continuous layer over ALL tooth-
contacting portions of the framework. The advantage
of this medium is that it is thin and accurate and is not easily displaced from the
framework. A disadvantage of this technique is that it provides only two-
dimensional assessment of fit. The technique was originally described with
chloroform instead of alcohol. Chloroform dries more quickly, but should not be
used as it has been shown to be potentially carcinogenic. An alternative to alcohol
and rouge is pre-packaged spray type pigments (e.g. Occlude'P'). These can be
applied more quickly, and are non-carcinogenic. However, it is difficult to obtain a
thin layer.

Advantages:      i. It is easy to apply   ii. Identifies interferences well.

Disadvantages: i. It is difficult to remove ii. It has carcinogenic potential.



2.     Disclosing wax: A small amount of wax is
removed from the jar and placed on a mixing pad. A
warmed instrument (#7 wax spatula, PKT waxing
instrument, etc.) is used to pick up and melt a portion
of the wax. The melted wax is applied in an even coat
over ALL tooth-contacting portions of the framework. The wax is allowed to gel
prior to placement in the mouth. The advantage of this medium is that it provides


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                                                                         Try-in of RPD


three-dimensional assessment of fit. Areas of burn-through indicate possible areas
of binding, and the thickness of the remaining wax indicates how far the rest of the
framework is from contact with the teeth. A disadvantage of wax is that it can
stick to teeth or be wiped away easily if the framework is seated improperly.

Advantages :

i. It provides three dimensional representation of framework adaptation

ii. It shows the degree of interference.

Disadvantages:

i. It requires a flame source.

ii. It is relatively difficult to remove.

3.     Silicone impression materials or indicating medium (e.g. Fit Checker™):

These materials can also be used as three-dimensional
indicators. A disadvantage of elastic materials is that they can
tear or pull off the framework. In addition, time is required for
set of the materials. In this regard the silicone fit-checking
media are more useful since they have shorter working times.

Advantages

i. They are easy to read,                   ii. Easy to remove from the framework,

iii. Provide a three-dimensional model

Disadvantages

i. They are expensive,                      ii. Require mixing, and

iii. Need time for the material to set.



                                       Mostafa fayad                                 32
                                                                          Try-in of RPD


4. Spray type Powders (Occlude): A small amount is sprayed in an even
continuous layer over ALL tooth-contacting portions of the framework. The
advantage of this medium is that it is thin and accurate and is not easily displaced
from the framework. The material can get quite thick if over-sprayed. Teeth,
tissues and the framework must be dry to prevent the pigment bleeding and
making reading of the indicator difficult. A disadvantage of this technique is that it
provides only two-dimensional assessment of fit.

 Advantages

       i. It marks areas of interference well           ii. Is easy to clean off.

 Disadvantages

       i. It is expensive,

       ii. There is potential for applying too thick a layer of material, and

       iii. It is difficult to work with in a wet environment

 5. Accufilm disclosing film:

 AccuFilm is a unique liquid that lets you mark anything
 including highly glazed porcelain or interproximal walls
 or the inner surfaces of a casting.

 Advantages

        i. It marks interferences well and

        ii. It is not as messy as some of the other media

 Disadvantages

        i. It is relatively difficult to manipulate intraorally and




                                       Mostafa fayad                                33
                                                                      Try-in of RPD


       ii. There is the potential for false positive results.

 6. Air abrasion with 50 m aluminum oxide:

 Advantages

       i. It identifies areas of interference well and

       ii. It is a clean method of disclosing.

 Disadvantages

       i. It requires access to air-abrading equipment, and

       ii. Extended use of air abrasion may affect adaptation of the framework by
       abrading the intaglio surface of the framework.

Clinical Adjustment

Binding against one or more of the abutment teeth can cause inadequate seating of
a framework. The area(s) of binding cannot be located without the use of an
indicating medium.

              Pressure indicating paste , rouge dissolved in chloroform or
              disclosing waxes are used as follows :

      a-The disclosing material is placed on all framework surfaces that will
      contact the teeth .

      b- The framework should be aligned over the abutment teeth and finger
      pressure applied in the direction of the planned path of insertion .

      c- The framework should be carefully removed from the mouth and then
      examined under magnification . The most common points of metal show
      through or high spots that interfere with seating occur above the survey line
      on the teeth . These usually occur under rests , shoulder of circumferential


                                    Mostafa fayad                               34
                                                                       Try-in of RPD


       clasp, under embrasure clasp and in interproximal extensions of lingual
       plating .

       d- The located areas of interference , should be relieved by grinding .

       e- The entire procedure is repeated until the framework is seated .

Use of Indicating Media (technique described for wax but applicable for
all media)

1.     Attempt to place framework intraorally. If gross resistance to placement is
felt, remove and coat with indicating medium. If the framework seats, ask the
patient if they feel the framework pulling on any teeth. The latter sensation will be
caused by active engagement of abutment teeth. Inquire as to the overall comfort
of the framework.

2.     Remove the framework and coat it with indicating medium. Align the
framework over the abutment teeth and use finger pressure over rest seats along
the path of insertion. DO NOT PLACE PRESSURE OVER GRIDWORK OF
DISTAL EXTENSIONS as this will fulcrum the framework. If gross resistance to
seating is encountered, remove and inspect for areas of burn-through. Have an
instructor inspect the framework. Relieve areas of binding as indicated. Repeat
until seating is achieved. The master cast can be inspected for areas of abrasion
that may indicate areas of gross binding as well.

3.     Once the denture can be seated, coat with wax and seat along the path of
insertion again. Use firm even pressure over the rest seats and or indirect retainers.
A mirror handle can be used for seating purposes. Use care in removing the
framework, as removal along the wrong path of insertion will change the markings
in the wax.




                                    Mostafa fayad                                  35
                                                                       Try-in of RPD


4.     Use caution in adjusting the framework. The clinician must differentiate
between normal and abnormal contacts. Guiding planes normally will exhibit long
vertical areas of contact, but broad areas of complete burn-through may indicate a
binding contact on the guiding plane. Similarly, the retentive tip of direct retainers
will normally exhibit burn-through, but active clasp retention must be eliminated
after the framework is fully seated. Therefore, the first step in adjustment is to
ensure complete seating.

       Experience is required to differentiate between normal and excessive
marking of the indicator medium. Adjustments can be made with small round
carbide burs, white stones or rubber abrasive points, depending on the position and
extent of binding. Do not use excessive force or the framework may be bent. Heat
generation is one of the reasons major adjustments are made prior to acrylic
placement (i.e. the heat would melt the acrylic).

5.     Completely remove the wax contaminated with metal grindings and place
fresh wax. Repeat this procedure until full seating is achieved. At this point a thin,
even film of wax should be observed under rests and indirect retainers. The wax
will have a greyish hue from the underlying metal. The feel of the denture upon
seating will change from a grating or snapping sensation to one of a gliding
sensation. Normal adjustment of a framework should take no longer than 20
minutes.

6.     Check for soft tissue impingements using pressure-indicating paste.
Remove a small portion from the jar, and place it on a mixing pad. Use a stiff-
bristled brush to spread a thin layer over the tissue surfaces of the major
connector, and infrabulge clasps. Leave streaks in the paste. Place intraorally with
moderate pressure and remove. Relieve any areas of marked burn-through. If
streaks are left in the paste, this indicates no contact with the tissues. Adjust or




                                    Mostafa fayad                                 36
                                                                      Try-in of RPD


leave accordingly. Maxillary palatal connectors should exhibit broad even contact
with the palate.

7.     If the framework cannot be adequately adjusted, it should be remade. In
some cases this decision may be made at the pre-clinical inspection stage. Make
this determination early, so that time will allow for a new impression to be made.
Determine if the casting fits similarly on the cast and in the mouth. If it does not,
the final impression was most likely inaccurate and should be remade. If the
casting does fit similarly, the discrepancy may be due to laboratory errors. In
many cases abrasion of the master cast will require re-making of the final
impression as well. If the pre-clinical inspection leads the dentist to believe a
remake is a possibility, a new custom tray should be made prior to the patient
appointment in anticipation of the need for a new impression.




                                    Mostafa fayad                                37
                                                                  Delivery of RPD

                Delivery of the Removable Partial Denture

I- Extraoral (visual) examination of the denture

II. Intraoral examination:

  A. Objectives:

        a. Correcting the acrylic denture base.

        b. Correcting occlusal discrepancies

        c. Adjusting retentive clasps.

  B. Checking of:

        a) Fit of the Denture Base:

        b) Checking up the denture stability:

        c) Checking denture retention

        d) Soft tissue adaptation.

        e) Abutment tooth adaptation.

III- Patient instructions:

             Post insertion review

IV - Maintenance

V - Post placement adjustments

                                      -----------------




                                                          Mostafa Fayad 1
                                                                          Delivery of RPD

I- Extraoral (visual) examination of the denture

To ensure that:

  a. The borders should be rounded and not sharp.

  b . The impression surface should not have any sharp
  edges.

  c. The polished surface is smooth and highly polished.

  d. Any acrylic ‘pearls’ should also be removed.

  e. Elimination of acrylic resin entered the gingival sulcus adjacent to the natural
  teeth.

  f. The duplicate casts (If present) should be examined for signs of abrasion
  produced by forcing rigid portions of the denture into place. Such abraded areas
  indicate parts of the denture, which may require adjustment.

II. Intraoral examination:

A. Objectives:

           a. Correcting the acrylic denture base.

           b. Correcting occlusal discrepancies

           c. Adjusting retentive clasps.

   a. Correcting the acrylic denture base.

   Objective:

   1. Identify and elimination "show through" that would prevent the denture from
   seating properly.

   2. Adjusting the peripheral extensions: No border over extensions, especially in
   the posterior palatal area, buccal shelf area, and the frenum areas.



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                                                                  Delivery of RPD

Identify and elimination "show through"

         The denture is seated in the mouth.

         If acrylic resin has entered the gingival sulcus adjacent to the
           natural teeth, the resultant sharp ridge of acrylic should be
           eliminated. Care must be taken not to remove excess material,
           since the soft tissues are liable to proliferate into the space so
           created.

         Along the planned path of insertion and withdrawal. If it does not
           seat, it is likely to be due to acrylic having entered undercuts
           related to the natural teeth or the alveolar ridges.

         The area of acrylic involved may be detected by visual inspection
           or by the use of pressure indicating past.

         If the interference with insertion is related to a flange, blanching of
           the mucosa as attempts are made to pass the acrylic flange over the
           most prominent part of the alveolar ridge may indicate the area
           responsible.

         The acrylic resin, which hinders insertion of the denture, is
           removed, taking care to preserve the contact between denture and
           hard and soft tissues in the non-undercut areas.

         Once the denture is seated and is comfortable the fit of all its
           components is checked.

   Modifying the Peripheral Extension of the Denture Base:

         Checking of the correct extension of the periphery should be
           performed visually, and digitally.

         The cheek is held between the thumb and index fingers, and moved
           downward, outward and upward (for lower denture) or moved
           upward, outward and downward (for upper denture).

                                                         Mostafa Fayad 3
                                                                    Delivery of RPD

             As the buccal tissue adjacent to the denture border during this
               movement is observed, any tissue trapped by the denture base is
               identified.

             To check the lingual extension of the lower distal extension base,
               the patient is instructed to thrust tongue forward and into the cheek
               of the opposite side of the mouth tested, while the operator placing
               the index finger on the occlusal surface.

             If there is any overextension it should be corrected by grinding.

b. Correcting occlusal discrepancies

1. Maximum intercuspation. Posterior teeth should demonstrate bilateral,
simultaneous contact. Anterior teeth should demonstrate the appropriate
relationship to opposing teeth.

2. Occlusal vertical dimension. The partial denture should demonstrate occlusal
contacts at the correct occlusal vertical dimension. Verify that the RPD is not
increasing the vertical dimension.

3. Articulation. The partial denture components should demonstrate appropriate
occlusal contacts with the opposing dentition or restorations during excursive
mandibular movements.

4. Adjustments.

     a.   Tooth borne partial dentures. The occlusion and articulation can usually
     be evaluated and adjusted intra orally.

     b. Tooth-mucosa borne partial dentures. The evaluation and adjustment of
     the occlusion and articulation usually require a clinical remount procedure.
     The displaceability of the muco-osseous segment allows the extension base
     to move tissue-ward during occlusal loading forces. Deflective occlusal
     contacts usually cannot be evaluated intraorally.



                                                           Mostafa Fayad 4
                                                                    Delivery of RPD

Materials of locating occlusal interferences:

a. The use of articulating paper.

b. The use of occlusal indicator wax. It may be obtained as a special item that is
supplied with one surface of the wax treated with an adhesive so that it adapts
firmly to the teeth being studied.

c. Thin sheets of regular casting wax, 28or 32-gauge.

          Intraoral method:

               Articulating        paper   or   occlusal
                 indicator wax may be used as a mean
                 of identifying occlusal contacts.

               This Intraoral technique can be used
                 only when the partial denture being corrected are stable in the
                 mouth (e.g. class III RPD).

          Technique:

                  With the partial denture out of the mouth, a two opposing
                    natural teeth that are contact in centric occlusion are selected
                    (as index).

                  Insert one partial denture into the mouth and get the patient
                    closing in centric occlusion, and note the selected index teeth,
                    if they are not contacting, articulating paper is used to locate
                    interference, which must be relieved until the index teeth
                    getting in contact.

                  Then interference in centric relation and protrusive and lateral
                    excursions must be corrected.

                  For patients receiving two removable partial dentures, after
                    adjustment of one partial denture, the same procedures are
                    followed with the opposing partial denture.
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                                                   Delivery of RPD

 After each denture has been corrected individually, correction
   for interference with both dentures seated in the mouth is
   performed.

 The artificial teeth must be carefully adjusted until the natural
   teeth meet in precisely the same way with or without the
   denture in place.

 Where natural teeth do not indicate the desired jaw
   relationships, the artificial teeth must be adjusted to provide
   even occlusal contact at the optimal occlusal vertical
   dimension in the retruded jaw relationship. Further adjustment
   should be undertaken to permit even contact to be maintained
   in an intercuspal position slightly anterior to the retruded
   contact position. In lateral and protrusive excursion the
   denture teeth should normally be adjusted so that they do not
   disturb the guidance offered by the remaining natural teeth.

 The articulating paper should be applied bilaterally in order to
   discourage deviation on closure of the mandible. Heavy tooth
   contact is indicated by ‘target’ markings, having a light centre
   surrounded by a ring of ink transferred from the paper. Other
   marks, simply produced by the paper taking up the space
   between the teeth, are generally less distinct and lack the
   lighter centre. The paper is relatively thick, and care must be
   taken to grind only those marks that indicate actual tooth
   contact.

 In those cases, where the partial denture saddles are extensive
   and the guidance in excursion from the remaining natural teeth
   allows the maintenance of bilateral balancing contacts, the
   following method of occlusal adjustment should be adopted:




                                          Mostafa Fayad 6
                                                     Delivery of RPD

 In intercuspal position The upper palatal cusps and lower
    buccal cusps (supporting) cusps contacting the fossae of their
    opposing teeth maintain the occlusal vertical dimension:

   If one of these cusps contacts prematurely when the patient
    attempts to reach intercuspal position and is also premature in
    lateral excursions, the cusp is reduced in height.

 If the cusp contacts prematurely on closure as before, but is
    not premature in lateral excursions, the fossa is deepened.

 Once even occlusal contact is achieved at the desired static
    jaw relationship, further adjustment of the supporting cusps
    should be avoided if possible.

 • In lateral excursion, if a premature contact occurs between
    a buccal upper cusp and a lower buccal cusp on the working
    side, only the buccal upper (BU) cusp is adjusted. If contact
    occurs between the upper palatal and lingual lower cusps, the
    lingual lower (LL) cusp is reduced. This method of adjusting
    tooth contact on the working side is thus called the BULL
    rule. If premature contacts on the balancing side occur
    between supporting cusps, such prematurities should be
    eliminated, wherever possible, by adjusting the height of
    supporting cusps.

 • In protrusive excursion, grinding the distal facing inclines
    of upper teeth and mesial facing inclines of lower teeth
    eliminates premature contacts.

 • As a final step, the occlusal anatomy of the posterior
    artificial teeth must be restored to re-establish the functional
    efficiency of the occlusion. Sluiceways and supplemental
    grooves should be added to occlusal surfaces to create escape


                                           Mostafa Fayad 7
                                                               Delivery of RPD

               ways for food and to act ascutting blades to increase the
               Chewing efficiency.

          • The patient is invited to check the appearance of the dentures
               so that any further minor modification can be carried out.
               After adjustments to the dentures have been completed, all
               areas that have been ground are repolished.

 Occlusal Correction by Remounting:

             In a small percentage of patients when stability is a problem as:

1. When all or nearly all the posterior occlusion is being restored and
locating discrepancies intraorally would be difficult if not impossible
(stability of the prosthesis is questionable).

2. When a complete denture is being constructed simultaneously with a
removable partial denture (so much of the occlusal scheme is being
restored).

     An irreversible hydrocolloid impression in a stock tray is          made
        while the partial denture is seated.

     The impression is poured into dental stone after blocking of the
        denture undercuts with wax.

     By using the face-bow transfer, the maxillary cast is mounted on
        the articulator.

     Then centric jaw relation records must be made to mount the
        mandibular cast.

     Articulating paper is used to locate interfering cusps and to help
        determine evenness of occlusal contacts.




                                                      Mostafa Fayad 8
                                                                      Delivery of RPD

   c. Adjusting retentive clasps.

             The denture should be retentive and stable. If free-end saddles rock
          about their most distal occlusal rests, this should be corrected by relining
          the saddles.

B. Checking of the following

a) Fit of the Denture Base:

          Painting the tissue surface of the base evenly with a thin coating of
             pressure indicating paste.

          The paste over the areas which preventing the partial denture from
             seating correctly will be displaced.

          This area or areas should be relieved.

b) Checking up the denture stability:

                 The framework components should be properly related to the
                   abatement teeth.

                 Checking of the stability by applying pressure anteriorly and
                   posteriorly alternatively.

                 The denture is stable when exhibit no movement under this test.

c) Checking denture retention:

                 The resistance to vertical dislodging force should be evaluated.

                 Modification of retentive components may be made to obtain
                   optimum retention, if needed.

                 The amount .of retention required is subjective as determined by
                   the dentist and patient.




                                                             Mostafa Fayad 9
                                                                          Delivery of RPD

d) Soft tissue adaptation

      1.        Evaluate the relationship of the components to the underlying soft
      tissues.

      a.        Components which should contact the soft tissues.

                i. Denture base.

             ii. Maxillary major connector, except where crossing the gingival
             margins.

      b.        Components that require relief from the soft tissues.

             1- Mandibular major connectors.

             Ii. Minor connectors and proximal plates. iii. Bar clasps.

      2.        Procedure for tissue surface adjustment.

           a.      Visually and digitally inspect the finished partial denture. Examine
                   closely for rough or sharp areas.

           b.      Apply a pressure indicating paste to the tissue surface.

           c.      Place the partial denture in the mouth and verify its complete seating.
                   Remove the partial denture and inspect the tissue surface for regions
                   of paste displacement.

           d.      Relieve the pressure areas where the paste has been displaced, using
                   an appropriate bur. Repeat the process until the areas of unfavorable
                   pressure have been removed.

           e.      The denture base areas of tooth-mucosa borne partial dentures should
                   also be examined while simulating occlusal loading forces under
                   finger pressure.

           f.      The tooth-mucosa borne partial denture should demonstrate the
                   required mucoosseous support. Simulated loading forces applied to
                   the extension base area usually should not cause the third point of
                                                                Mostafa Fayad 10
                                                                          Delivery of RPD

                   reference to be elevated from its tooth contact. When movement of
                   the third point of reference is noted, a relining of the base is usually
                   indicated.

     3. Evaluate the relationship of the components to the adjacent movable soft
     tissues. The partial denture should not impinge on movable soft tissues.

              a.       Denture base.

              b.       Major connectors.

              c.       Bar clasps.

       4.     Procedure for periphery adjustment.

         a.   Visually inspect the peripheral components of the seated partial denture
         in the mouth.

         b.   Manually activate or instruct the patient to move the lips, tongue, cheeks
         and jaw through simulated functional movement.

         c.   Where the periphery cannot be adequately observed and a question of
         peripheral extension exists, a disclosing wax may be utilized.

         d.   Modify the periphery as indicated by the visual or disclosing wax
         evaluation.

e) Abutment tooth adaptation.

The framework components should be properly related to the abutment teeth.

1.     The rests should demonstrate a complete and stable seating in their rest seats.

2.     The clasps, minor connectors, and proximal plates should demonstrate the
required contact with the abutment teeth.




                                                                Mostafa Fayad 11
                                                                            Delivery of RPD

III- Patient instructions:

A. MAINTENANCE OF THE PARTIAL DENTURE.

Describe and demonstrate proper maintenance procedures. Written instructions may
supplement the verbal communication.

1.     Brushing technique.

        a.    Use of a proper brush for the RPD.

        b.    Brush over a sink with water or a towel in it. This minimizes the
        potential for damage if the RPD is dropped.

        c.    Do not squeeze or bend RPD while brushing.

2.     Cleaning agents.

        a.    Hand soap.

        b.    Denture pastes or creams.

        c.    Soak cleaners may be used where stain accumulation is not controlled by
        brushing alone. Advise the patient to brush the RPD before and after soaking
        to maximize plaque and stain removal. Patients should be cautioned not to
        soak the RPD in a sodium hypochlorite (bleach) solution.

        d. Ultrasonic baths may be useful for patients who have difficulty brushing or
        as an adjunct cleaning procedure.

        e.    Patients should be advised not to use toothpaste or abrasive cleaners.

3.     Adjustments. The patient should be advised not to adjust their RPD. If any
difficulties with the fit or retention develop, they should contact their dentist.




                                                                 Mostafa Fayad 12
                                                                           Delivery of RPD

B.        CARE OF THE ORAL TISSUES.

1.        Tooth brushing technique. Demonstrate the proper technique of sulcular
brushing with a soft toothbrush.

2.        Flossing technique. Demonstrate the proper flossing technique.

3.        Adjunct devices. Where indicated, other devices may be recommended to
improve plaque control.

          a.     Floss holders.

          b.     Tooth picks.

          c.     Interproximal brushes

          d.     Mechanized tooth brushes.

4.        Brushing of mucosal tissues adjacent to or covered by the RPD with a soft
toothbrush.

5.        Plaque reducing rinses. Over-the-counter or prescription solutions may be
beneficial for patients who demonstrate less than optimal plaque control.

6.        Fluoride may be useful for patients who demonstrate an increased risk for
caries.

          a.     Rinses.

          b.     Gels.

          c.     Stents. Where patients demonstrate a high caries activity, stents may be
          used to carry a fluoride gel to the tooth surfaces.

          d.     Fluoride on RPD. RPD framework may be used to carry a fluoride gel to
          the tooth surfaces.

7.        The use of disclosing tablets is excellent way to disclose areas that are
susceptible to plaque accumulation.


                                                                Mostafa Fayad 13
                                                                         Delivery of RPD

8.     Brushing of the denture with denture and clasp brushes
and regular toothpaste or soap should be a routine. Abrasive
agents should be avoided.

9.     Removing of the accumulated calculus by scraping with hand instruments, or
by soaking the RPD in a full strength vinegar solution for at least 12 hours. (Using of
cleansing solutions containing chlorine should be completely avoided).

10.    The patient should be instructed to remove the prosthesis all over the night.
(Only in rare instances RPD should be worn at night).




C.     PLACEMENT AND REMOVAL OF THE PARTIAL DENTURE.

       The proper placement and removal of the RPD should be demonstrated. The
patient should be able to accomplish these procedures before leaving the office.

1.     Finger pressure should be used to completely seat the RPD.

2.     The patient should be cautioned not to seat the RPD with occlusal force (not
"bite" into place).

3.     Devices or modifications in the RPD may be required for patients who have
difficulty removing the RPD with their fingers.

       a.     Devices. Small smooth hooks placed in a toothbrush handle or modified
       dental hand instruments may aid the patient in removing the RPD.

       b.     Modifications. Grooves or slots placed in the denture base or artificial
       teeth may improve the patient's ability to engage the partial denture.

4.     The patient should be positioned in front of a wall-mounted mirror while the
dentist inserts the prosthesis. After the patient has observed insertion of the removable
partial denture, its removal also should be demonstrated. Before the patient being
dismissed, he should be asked to demonstrate the proper methods of RPD insertion and
removal for the dentist.


                                                               Mostafa Fayad 14
                                                                         Delivery of RPD

5.     Weak components must be pointed out; thus clasps should not be used as
fingernail holds during removal.

D.     WEARING THE PARTIAL DENTURE.

1.     Initial accommodation period. Patients should be given specific instructions to
facilitate adaptation to their new prosthesis.

       a.     Bulk. It may take several days to several weeks before the patient
       accepts the presence of the partial denture, especially for the inexperienced
       patient.

       b.     Speech. If the RPD alters enunciation, the patient should be instructed to
       practice reading aloud.

       c.     Mastication. The patient should initially masticate smaller portions of
       softer foods.

       d.     Saliva. A transient increase in salivary flow may be noticed initially.

       e.     Explanation of any expected difficulties and limitations of the dentures
       should be reinforced at the beginning of treatment.

       f.     Patient should be advised that muscular control takes time to develop; so
       small quantities of non-sticky food should be chewed on both sides of the
       mouth initially.

2.     Prosthesis should be removed from the mouth several hours daily to facilitate
tissue health. Several exceptions may be noted:

        a.    RPD that splints hypermobile teeth. Where the patient experiences
        difficulty or discomfort in placing RPD at the morning.

        b.    RPD that maintains the occlusal vertical dimension. When RPD prevents
        trauma to remaining natural teeth or mucosa, a splint may be used at night as a
        substitute for the RPD.




                                                               Mostafa Fayad 15
                                                                             Delivery of RPD

           c.    When the RPD is worn at night, the patient should clean the oral tissues
           and prosthesis before retiring and again in the morning.




Written instructions:

It is impractical to expect that all patients will remember all of the instructions
provided in the insertion visit, so providing the patient with written instructions will
permit him to review the instructions at home.




Post insertion review:

Post insertion difficulties should be expected by both the dentist and the patient;
however attention to details during the fitting and insertion visit will minimize, but not
eliminate all possible complications. Therefore the patient should return to his dentist
within 24 hours of partial denture insertion. This period is sufficient to allow detection
of initial signs of post insertion complications.

Methods of managing the complications depend upon the type of that complication.




IV - MAINTENANCE

A.     PERIODONTAL.

     1.          Recall intervals.

            a.   Shorter intervals for patients with active periodontal disease. (Two to
            four months).

            b. Longer intervals for patients without active periodontal disease. (Six to
            twelve months).

            c .. Consider shorter interval s initially after RPD delivery.

      2.         Plaque control instructions at each appointment.
                                                                  Mostafa Fayad 16
                                                                         Delivery of RPD

             a.      Intraoral hygiene procedures.

             b.      RPD maintenance procedures.

      3.      Evaluate periodontal health, especially RPD abutments.

      4.      Periodontal treatment as required.

B.    RESTORATIVE.

1.    Tooth examination.

      a.      Caries.

      b.      Defective restorations.

2.    Soft tissue examination. Examine all oral soft tissues, especially those adjacent
to or supporting the R

3.    RPD Examination.

     a.       Extraoral.

              i. Fracture of components. ii. Wear of artificial teeth.

     b.       Intraoral."

           1. Muco-osseous support. Apply pressure to extension base areas of tooth
           mucosa borne RPDs. Examine for movement of third point of reference
           indicating a need to reline the base.

           2. Retention and Stability.

           3. Occlusion and articulation.




                                                                Mostafa Fayad 17
                                                                           Delivery of RPD

     •   The patient should be given an appointment for review in approximately
         seven days’ time.

     •   The patient should be advised that if significant discomfort is experienced
         during the first week the dentures should be removed and should not be worn
         again until a few hours before the review appointment. This short period of
         wear often aids the location of the cause of the pain.

     •   The need for regular review of the mouth and denture should be emphasized.
         Not only may the natural teeth and periodontal tissues require treatment, but
         also it is necessary to prevent damage from the denture, which, in the initial
         stages, may be painless. For instance, free-end saddles may need to be relined in
         order to eliminate the rocking movement that could loosen abutment teeth and
         hasten loss of alveolar bone in the edentulous area. It must also be made clear
         that dentures have a limited life and therefore replacements will need to be
         constructed as appropriate.




V - POST PLACEMENT ADJUSTMENTS

A.       SOFT TISSUE ADAPTATION.

1.       Patient's subjective evaluation.

2.       Clinical examination of soft tissues.

3.       Adjustment.

         a.     Apply a pressure indicating paste to the involved tissue surface of the
         prosthesis.

         b.     Place the partial denture into the mouth and verify complete seating of
         the partial denture.




                                                                  Mostafa Fayad 18
                                                                    Delivery of RPD

     c.     An indelible pencil may be used to mark the mucosa in the pressure area.
     The mark transferred to the prosthesis may be used to confirm the area to be
     adjusted.

B.   OCCLUSION.

     1.     Patient's subjective evaluation.

     2.     Clinical examination.

           a.      Visual.

           b.      Articulating paper.

           c.      Wax.

           d.      Shim stock.

     3.     Adjustment.

C.   FRAMEWORK.

           1.      Clasps. The retention may be modified as necessary,

           2.      Minor connectors and proximal plates. The amount and location
           of tooth contact may be modified.




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                                                      !!REPAIRS AND ADDITIONS



   MAINTENANCE AND REPAIRE OF RPD

                                 Relining
Definition:
      Relining is the resurfacing of the tissue surface of a denture base
with new material to make it fit the underlying tissues more accurately,
Indications:
   1. Loss of tissue support that cause rotation of the distal extension
      base.
NB; in the bounded saddles loss of tissue contact leads to unpleasant
appearance, food traps, and/or patient’s discomfort.
      2. Loss of occlusal contact.

Diagnosis:
      In order to diagnose if the distal extension partial denture is n need
of relining,
      1- A pressure or force is applied on the extreme distal end of the
denture base and watching, if the anterior indirect retainer (rest seat) lift
off its rest preparation as the denture rotates around the fulcrum line; this
indicates that there is a tissue loss occurred, and a relining is required.
      2- Another method for diagnosis by using alginate impression as
indicating paste for the area needed for relining, Areas loaded with
alginate.




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                                                    !!REPAIRS AND ADDITIONS



RELINING TOOTH-SUPPORTED DENTURE BASES


A- NEED FOR RELINING
       Support for that restoration is derived entirely from the abutment
teeth at each end of each edentulous span. This support may be effective
through the use of occlusal rests, boxlike internal rests, internal
attachments, or supporting ledges on abutment restorations.
       Tissue changes that occur beneath tooth-supported denture bases
do not affect the support of the denture, and therefore relining or rebasing
is usually done for reasons that include
       (1) Unhygienic conditions and the trapping of debris between the
denture and the residual ridge;
       (2) An unsightly condition that results from the space that has
developed; or
       (3) Patient discomfort associated with lack of tissue contact that
arises from open spaces between the denture base and the tissues.
       (4) Anteriorly, loss of support beneath a denture base may lead to
some denture movement, despite occlusal support and direct retainers
located posteriorly.
       Rebasing would be the treatment of choice if the artificial teeth are
to be replaced or rearranged, or if the denture base needs to be replaced
for esthetic reasons or because it has become defective.


B- PROCSDURES OF RELINING
       Before relining or rebasing is undertaken, the oral tissues must be
returned to an acceptable state of health by conditioning abused and
irritated tissues.
       a- Resin base
Methods of relining:

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                                                     !!REPAIRS AND ADDITIONS



      A) Direct reline, intraoral reline (chair-side):
      It is entirely acceptable for most tooth supported partial denture
bases made of an acrylic resin material, except when some tissue support
may be obtained for long spans between abutment teeth. In the latter
situation, a reline impression in tissue-conditioning material or other
suitable elastic impression material may be accomplished.
Advantages:
   1. Saving time.
   2. The patient does not leave his denture.
    3. The direct reline materials are constantly improved with greater
predictability and color stability. The possibility that the original denture
base will become crazed or distorted by the action of the activated
monomer is minimal when the base is made of modern cross-linked
acrylic resin. However, caution should be exercised to be sure that the
older types of acrylic resin bases are compatible when relining with direct
reline acrylic resins.
      The vertical dimension of occlusion may be increased and that the
denture may be distorted during laboratory procedure


Disadvantages of intra-oral reline:
It may results in porous and non-hygienic base.


Procedure:
     Materials:
   1. Special auto polymerizing resins that are intended to be cured in
      the mouth.
   2. Visible light cured resin as a hard chair side relining.




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                                                    !!REPAIRS AND ADDITIONS



   3. Resilient relining can be used in case of severe atrophic ridge,
      irradiated and diabetic patients, and in presence of hyperplasic
      tissues.
      Technique
      1. Relieve the tissue side of the denture base. Lightly relieve the
borders. This not only provides space for an adequate thickness of new
material but also eliminates the possibility of tissue impingement because
of confinement of the material.
      2. Apply lubricant or tape over the polished surfaces from the
relieved border to the occlusal surfaces of the teeth to prevent new resin
from adhering to bases and teeth.
      3. Mix the powder and liquid in a suitable container according to
the proportions recommended by the manufacturer.
      4. While the material is reaching the desired consistency, have the
patient rinse the mouth with cold water. At the same time, wipe the
fresh surfaces of the dried denture base with a cotton pellet or small brush
saturated with some of the reline acrylic resin monomer. This facilitates
bonding and ensures that the surface is free of any contamination.
      5. When the material has first begun to thicken, but while it is still
quite fluid, apply it to the tissue side of the denture base and over the
borders. Immediately place the denture in the mouth in its terminal
position, and have the patient close into occlusion. Be sure no material
flows over the occlusal surfaces or altering the established vertical
dimension of occlusion. Then, with the patient's mouth open, manipulate
the cheeks to turn the excess at the border and establish harmony with
bordering attachments.
      If a mandibular partial denture is being relined, have the patient
move the tongue into each cheek and then against the anterior teeth to
establish the functional lingual border.

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                                                    !!REPAIRS AND ADDITIONS



      It is necessary that the direct retainers be effective to prevent
displacement of the denture while molding of the borders is
accomplished. Otherwise the denture must be held in its terminal position
with finger pressure on the occlusal surfaces while border molding is in
progress.
      6. Immediately remove the denture from the mouth and with fine
curved iris scissors, trim away gross excess material and any material that
has flowed onto proximal tooth surfaces and other components of the
denture framework. While doing this, have the patient again rinse the
mouth with cold water. Then replace the denture in its terminal position
to bring the teeth into occlusion. Then repeat the border movements with
the patient' s mouth open. By this time, or soon thereafter, the material
will have become firm enough to maintain its form out of the mouth.
      7. Remove the denture, quickly rinse it in water, and dry the relined
surface with compressed air. Apply a generous coat of glycerin with a
brush or cotton pellet to prevent frosting of the surface caused by
evaporation of monomer
      8. Allow the material to bench cure in a container of cold water
this will eliminate any patient discomfort and tissue damage that could
have resulted from exothermic heat or prolonged contact of the tissues
with raw monomer.
      Although it is preferable that 20 to 30 minutes elapse before
trimming and polishing, it may be done as soon as the material hardens-
Polymerization may be expedited and condensed by placing the denture
in warm water in a pressure pot for 15 minutes at 20 psi.
      The masking tape must be removed before trimming is done but
should be replaced over the teeth and polished surfaces below the
junction of the new and old materials to protect those surfaces during
final polishing

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                                                   !!REPAIRS AND ADDITIONS




      Metal base
      A metal base is not used in a tooth supported area in which early
tissue changes are anticipated. A metal base should not be used after
recent extractions or other surgery or for a long span when relining to
provide secondary tissue support is anticipated.
       Commonly, tooth supported partial denture bases are made of
metal as part of the cast framework. These generally cannot be
satisfactorily relined, although they may sometimes be altered by
      1- Drastic grinding to provide mechanical retention for the attach-
ment of an entirely new acrylic resin base.
      2- Using some of the new acrylic resin bonding agents, such as
Four-meta, Silicoating, or Rocatec.


B) Laboratory relining:
      Procedure:
   • Removing a uniform amount of denture base resin from the tissue
      side of the base as well as all undercuts.
   • Sufficient space is allowed beneath the denture base to permit the
      excess material to flow to the borders, where it is either turned by
      the bordering tissues or, as in the palate, allowed to escape through
      venting holes without unduly displacing the underlying tissues.
   • Impression material which used that will record the anatomic form
      of the oral tissues.
   • A closed mouth impression technique is performed (because the
      tooth-supported denture base cannot be depressed beyond its
      terminal position with the occlusal rests seated and the teeth in
      occlusion, and because it cannot rotate about fulcrum) by asking



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                                                        !!REPAIRS AND ADDITIONS



        the patient to close in centric occlusion until complete setting of the
        impression material.



.   RELINING DISTAL EXTENTION DENTURE BASES
A- NEED FOR RELINING
     The need for relining a distal extension base is determined by
evaluating the stability and occlusion at reasonable intervals after initial
placement of the denture.
     There arc two indications of the need for relining a distal
extension partial denture base.
     1- A loss of occlusal contact between opposing dentures or between
the denture and opposing natural dentition:
     This is determined by having the patient close on two strips of 28
gauge soft green or blue (casting) wax or Mylar matrix strips.
     If occlusal contact between artificial dentition is weak or lacking while
the remaining natural teeth in opposition are making firm contact, the
distal extension denture needs to have occlusion reestablished on the
present base by
        • Altering the occlusion
        • Reestablishing the original position of the framework and base
        • Sometimes both.
     In most instances, reestablishing the original relationship of the
denture is necessary, and the occlusion will automatically be
reestablished.
     2- A loss of tissue support that causes rotation and settling of the distal
extension base or bases
     It is obvious when alternate finger pressure is applied on either side of
the fulcrum line.


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                                                         !!REPAIRS AND ADDITIONS



   Although checking for occlusal contact alone may be misleading, such
rotation is positive proof that relining is necessary.
   If occlusal inadequacy is detected without any evidence of denture
rotation toward the residual ridge, all that needs to be done is to
reestablish occlusal contact by
      • Rearranging the teeth or
      • Adding to the occlusal surfaces with resin or cast gold onlays.
   If denture rotation can be demonstrated, but occlusal contact is
adequate, it is usually a result of migration or extrusion of opposing teeth
or shift in position of an opposing maxillary denture, thus maintaining
occlusal contact at the expense of the stability and tissue support of that
denture.
   This is often the situation when a partial denture is opposed by a
maxillary complete denture. It is not unusual for a patient to complain of
looseness of the maxillary complete denture and request relining of that
denture when actually it is the partial denture that needs relining. Relining
and thus repositioning the partial denture results in repositioning of the
maxillary complete denture with a return of stability and retention in that
denture.
   Therefore evidence of rotation of a distal extension partial denture
about the fulcrum line must be the deciding factor as to whether relining
needs to be done.


B- PROCSDURES OF RELINING
Laboratory relining
   • As in bounded saddle relining except some differences




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                                                     !!REPAIRS AND ADDITIONS



   • Open mouth impression technique is used, and the dentist must
      hold the framework against the abutment teeth until the impression
      material sets.
   • Dentist’s three fingers placed on the two principal occlusal rests
      and at a third point between, preferably at an indirect retainer
      farthest from the axis of rotation.
   • The completed partial denture reline impression is presented to the
      laboratory for processing.



Re-establishing occlusion on a relined partial denture:
      A loss of occlusal contact of a distal extension partial denture and
opposing teeth may be automatically established when performing a
relining. But re-establishing of the occlusion may be indicated due to:
   1. Migration or extrusion of opposing natural teeth.
   2. Shifting in position of an opposing complete denture and occlusal
      disharmony.
   3. Wearing of the occlusal surface over a period of time. This tooth is
      restored by chemical-curing resin.


      If the artificial teeth to be corrected arc acrylic resin, the occlusion
can be reestablished either by
      1- Adding auto polymerizing or light-activated acrylic resin to
occlusal surfaces or by fabricating gold occlusal surfaces, which can be
attached to the original replaced teeth.
      2- The original teeth may also be removed from the denture base
and replaced by new teeth arranged to harmonize with the opposing
occlusal surfaces.




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                                                     !!REPAIRS AND ADDITIONS



                                Rebasing

Definition:
       Rebasing is the replacement of the entire denture base with new
material while preserving the occlusal relationship. The artificial teeth
may need to be replaced in a rebase procedure.


Indications:
   • When the denture borders do not extend to cover all the supporting
       tissue.
   • When the denture is fractured in the denture base.
   •   When the denture is stained or discolored.


Technique:
First Technique
    The tissue side denture base is relieved as in relining.
    Modeling plastic is then added in small increments for border
       molding.
    Covering of the base with the suitable impression material for
       making the final impression.
    The rebase impression is flasked directly without pouring a cast.
    After opening the flask the traces of the impression material and
       wax are removed and the old resin is removed.
    Packing of acrylic resin, curing, deflasking, finishing and polishing
       is carried out.




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                                                        !!REPAIRS AND ADDITIONS



Second Technique
1- The tissue surface of the denture base is relieved and trimmed to provide
space for re adaptation of borders with modelling plastic.
2- Border moulding is done.
3- After border moulding, a final impression is made using the framework.
4- A cast is poured against the rebase impression.
5- The modelling plastic and the final impression material is scrapped away
from the denture base.
6- The denture base extending over the area to be rebased should be trimmed
leaving just about 2-3 mm adjacent to the base of the teeth.
7- When the anterior teeth are involved, the junction of the new resin and the
existing denture base should be kept in an area that is not visible. A faint line
will always exist at this junction and it may be visible when the patient smiles.
8- This observable line is reduced when the borders of the resin are at 90º to the
external surface. If aesthetics is not important, the junction should be rounded
to reduce the stress concentration and to increase the strength. 9- Now the
framework with the trimmed denture base will not contact the edentulous ridge.
10 - The contour of the denture base is re-established by adding small amounts
of base plate wax. This gives a finished contour to the processed rebase and
reduces the finishing time.
11- Flasking is done.
12- A boil-out procedure is done to soften the wax and modelling plastic.
13- The tissue surface of the denture resin is trimmed to provide space for the
new resin. This trimmirtg should stop short of the denture teeth.
14- Acrylization and processing is done as usual.
15- The denture is de-flasked using a lab knife or pneumatic blade and a shell
blaster.
16- Finishing and polishing is done.




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                                                       !!REPAIRS AND ADDITIONS



              REPAIRS AND ADDITIONS TO RPD

      Accidents or careless handling of the denture by the patient might result
in a need for denture repair. The following are some of the repair procedures
which might be necessary in these cases.

A] Broken clasp arms
       The most common type of repair is the replacement of a broken
  retentive clasp arm,
       causes:
         - 1- Repeated flexure into and out of a deep undercut. This can be
           avoided by placing retentive tips of clasp arms in undercuts where
          an acceptable minimum retention is gained as determined by an
          accurate survey of the master cast.
         - 2- Structural failure of the clasp arm: This occurs when the clasp
          arm is not uniformly tapered. it can be prevented by providing the
          appropriate taper to flexible retentive clasp arms and uniform bulk
          to all rigid non retentive clasp arms.
         - 3- Careless handling by the patient.
         - It can be prevented by cautioning the patient against removal of P.d.
           by sliding the clasp arm away from the tooth with fingernails
         - 4- Accidental dropping of the denture.
         - 5- Re crystallization of wrought wire clasp resulted from
           overheating so it is better to solder the wrought wire clasp to the
           frame work electrically.

               A broken retentive clasp arm, regardless of its type, may be
          replaced with a wrought-wire retentive arm embedded in the resin
          base or attached to a metal base by electric soldering.

 Repair is done in the following manner
         - The remaining part of the original clasp arm is first cut off flush
           with the point of origin of the clasp.




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                                                           !!REPAIRS AND ADDITIONS


          - A hole is then drilled just below the adjacent denture tooth. From
            this hole a groove is cut in the resin base long enough to
            accommodate sufficient length of the wrought wire.
           - A piece of 18-gauge wrought wire is shaped and adapted to fit the
             groove.
          - A right angle bend is made at the end of the wire.
          - A straight portion is left emerging from the resin base at the point of
            origin of the new clasp arm.
          - The projecting wire is then cut off to the required length and
            adapted to the abutment tooth on the master cast to serve as a new
            retentive clasp arm. The wire is fixed to the base with chemically
            activated resin.
           Because of the flexibility of the wrought wire, it cannot be used to
    replace a rigid stabilizing clasp arm. In such case, it is better to entirely
    cast a new clasp assembly and attach it to the framework by soldering. The
    resin base must to be protected with wet asbestos during soldering. Gold
    solder is used for soldering both gold and chrome-cobalt alloys. A colour-
    matching white gold solder is preferred for the chromium-cobalt alloys.

 B] Broken Occlusal Rests
            Causes
            Breakage of an occlusal rest almost always occurs at the point
       where it crosses the marginal ridge due to weakness at this point.
       Breakage may be due to improperly prepared occlusal rest seat or
       reduction of occlusal rest to adjust occlusal interference from the
       opposing dentition. it rarely occurs due to structural defect of alloy used.
            Treatment:
            Repairing a broken occlusal rest may first require alteration of the
       occlusal rest seat preparation and/or relieving an opposing occlusal
       interference.
            Broken occlusal rests may be repaired by soldering a new rest in
       the following manner:
- The partial denture is adequately seated in the mouth.


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                                                          !!REPAIRS AND ADDITIONS


- An alginate impression is made. After setting, the impression is removed with
  the denture inside it.
- Dental stone is poured into the impression to form a cast.
- The denture is removed from the cast.
- Platinum foil is adapted to the rest seat and over the reduced marginal ridge.
- The partial denture is returned to the cast and a gold solder is used to fuse the
  platinum foil to the minor connector.

        N.B.: In case of broken occlusal rest it is always best to replace the
               whole clasp assembly.

 C] Distortion of Major or Minor Connectors
              Causes:
              Although major and minor connectors are constructed with
       sufficient bulk, breakage may result due to abuse by the patient or
       excessive adjustment and grinding during denture insertion in order to
       avoid tissue impingement.
              Treatment:
              The distorted connector usually looses rigidity. It can no longer
       function effectively. Hence it is preferable to make a new restoration.
 D] Loss of an additional natural tooth
              If a natural tooth is to be extracted the procedure of adding such
       tooth is simple when the partial denture base is made of acrylic resin.
              However when the denture base is made of metal the procedure
       will be more complex.
             If the lost tooth is not abutment ,it necessitates either casting a
       new component and soldering it to the denture base or creating retentive
       elements as perforation or soldered wire is created for the attachment of
       an acrylic resin extension to place the missed tooth.
              If the abutment tooth which supporting the clasp arm is lost. The
       clasp arm is cut off the framework. The next adjacent tooth is modified
       by preparing an occlusal; rest seat and guiding planes. A new clasp
       assembly is cast for the new abutment and soldered to the framework.


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                                                           !!REPAIRS AND ADDITIONS



                               Denture Base Repair
   •   If the broken segments are available and can be accurately re-positioned,
       the section are held together and luted with sticky wax along the fracture
       line.
   •   Dental stone is poured against the tissue side of the denture base. When
       the stone sets, the denture is removed and the sticky wax is cleaned.
   •   The denture is separated along the fracture line.
   •   The fractured margins are dovetailed.
   •   The separating medium is applied over the cast.
   •   The pieces of denture are assembled and held in position.
   •   Auto-polymerizing resin is added along the fracture line by sprinkle-on
       method.
   •   It is placed in a heated pressure pot to complete the curing.

       If the broken segments are lost or cannot be re-positioned, they are
discarded. In such cases, the modelling plastic is added and contoured in the
defective area. The impression is made without displacing soft tissues. The
repair is done as a rebase procedure.

                Replacement of Denture Teeth
   •   An accurate opposing cast and a jaw relation record is necessary.
   •   The tooth of the same mould and shade is selected and set in the space
       produced by the missing tooth.
   •   Access should be gained by opening through the lingual surface. The
       labial or buccal denture base should be preserved.
   •   The ridge-lap area should be relieved to allow at least 2 mm of repair
       resin to bind the tooth to the base.
   •   The tooth is luted to the framework with sticky wax.
   •   Auto-polymerizing resin is added with a fine brush If multiple teeth are
       to be replaced, a mounting cast is poured against the tissue-surface of
       the RPD.



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                                                             !!REPAIRS AND ADDITIONS


      •   This cast is articulated with the opposing cast.
      •   Teeth to be replaced are positioned and finally the denture base is
          relieved.
      •   Gingival contours are waxed and the denture is flasked, packed and
          processed.

                                 RECONSTRUCTION OF RPD
         The partial denture is reconstructed by removing the resin and denture
    teeth from the framework The existing framework can be re-used if it has a
    clinically acceptable fit.
    Indications
    When the denture base is damaged beyond repair.
    When the fit of the denture is not satisfactory .
    Loss of aesthetics, function, etc.

    Procedure
• The resin is removed from the tissue side while holding the framework in a cotton
     forceps or haemostat (artery forceps).
• The framework is sandblasted to remove the residue and re-polished.
• The framework is seated in the mouth and an alginate impression is made over it.
• The framework should come out along with the impression. If it remains in the
     mouth (separated from alginate), the retentive clasp arms should be adjusted to
       reduce retention and the impression is remade.
• In order to accurately record the tissues in the retentive meshwork area, the
      impression material must be forced into the mesh by applying finger pressure.
• Cast is poured with dental stone.
• The framework is carefully separated from the stone cast by lifting it along the
     inferior border of the major connector.
• Force should not be applied as it can distort the retentive clasp arm.
• dual impression can be made (if needed)
• Then the RPD is articulated and fabricated as usual.


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                                                         !!REPAIRS AND ADDITIONS



              Restorations under Existing RPDs
       The two or three surface alloy restoration that fractures at the isthmus is
difficult to place under an existing partial and maintain positive contact with
the rest. In these instances, the tooth usually requires re preparation of the box
form to widen or deepen or some combination of the two, to ensure that an
adequate bulk or amalgam is present.

       These restorations may also be made in composite. Since the composite
filling can be layered into the cavity; the final contact with the rest or other
component of the partial cam be made, after the removal of the rubber dam and
matrix. Light activation or the composite is usually possible in a two stage
process where the material is first activated with the partial in place. This will
usually set the material sufficiently to allow removal of the partial denture
without distorting the restoration. Additional light curing with the partial out of
the mouth completes the restoration .

       For those situations in which a complete composite restoration is not
indicated, a combination of alloy and composite can be used to support an
occlusal rest. After the additional mouth preparation, the alloy is packed in the
usual manner and then a dovetailed box in the area of the rest is formed.
Chemically curing composite is placed in the box and the partial is fully seated
in the mouth until completely cured. This combination of restorative materials
will allow the creation of a positive rest.

              Crowns under Existing RPDs
      The impression is made by removing the retraction cord and injecting the
low viscosity impression material of choice completely around the margin of
the preparation. A small amount of Impression material can be injected onto
the remainder of the prepared tooth. An excess of material might restrict the
full seating of the partial.
       The impression must he made with the partial denture in its proper
relationship tot he supporting abutment teeth. This requires a sectional



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                                                         !!REPAIRS AND ADDITIONS


impression with the clinician holding the partial in position while the assistant
seats the sectional tray.
        The partial denture is seated in the mouth, and additional material is
syringed onto the prepared tooth and into the space between the tooth and the
partial. Once the space is filled with the low-viscosity material, the sectional
tray can be seated. This tray must extend on either side of the repair area so that
there will be sufficient impression material to lock the partial into the
impression.
       The master cast is then poured. It is critical that the stone is poured
directly against all parts of the partial denture with the exception of clasp arms,
precision attachments, and undercut s in the resin areas.
       The technician marginates the die and wax the crown to fit the
framework. This is usually done by first waxing a thin coping to the margins.
The casting is then seated on the cast. and molten wax is flowed in the space
between the coping and the casting using a glass eye dropper that have been
warmed in the flame to prevent the wax from cooling too quickly.

       The most difficult part of the repair is waxing the area where the clasp,
should there be one, will lie. not only will the wax need to flow against the
internal area of the clasp arm , but a retentive contour will have to be built into
the wax-up.

       If the crown is to have a porcelain veneer
        The task becomes even more difficult; since the porcelain must he
overbuilt originally. As a result, the frame can’t be removed from the crown
without fracturing off the dry porcelain. The solution to these problems is to
sacrifice the retentive clasp arm and make the facial contour to ideal
dimensions. Alter the porcelain veneering is complete. With appropriate
undercut in place, a repair clasp is added to the partial




                                                                    Mostafa Fayad 18

				
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Description: Partial Denture FAYAD