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Designing RPD 321_1_

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									                  SDS – 321


McCracken’s Removable Partial Prosthodontics.
              Chapter 10 & 19
   ‘Our objective should be the perpetual preservation of what remains
    rather than the meticulous restoration of what is missing’.
Preserving what remains
                         Designing RPD




   ‘On the basis of information gathered from the clinical examination
                  and the analysis of the study casts, …
                  Designing RPD




… the components of an RPD framework are so
selected that the resulting design is esthetically
pleasant and is least harmful to the remaining tissues’.
 As a result of the examination and diagnosis, the
  design of an RPD must originate on the diagnostic
  cast so that all the mouth preparation are carried out
  with a specific design in mind. This could be
  influenced by the following factors,
   Factors influencing the RPD Design




1. One arch is to be restored or both
        a. Orientation of the occlusal plane.
        b. Space available for restoring missing teeth.
Factors influencing the RPD Design

Vertical space

                                                 Overlay rest
                                  Over-denture


                 Retentive area
                                                    Long rest

                                  Over-denture




c. Occlusal relationship of the remaining teeth.
d. Arch integrity and tooth morphology.
           Factors influencing the RPD Design




2. Remaining abutment support / periodontal health / need for splinting
                         or future additions.
 Factors influencing the RPD Design




3. Tooth or Tooth & tissue supported prosthesis.
 Factors influencing the RPD Design




4. Need for abutment modification – clasp design.
   Factors influencing the RPD Design




 5. Type of major connector indicated – e.g., a torus.
6. Materials to be used for framework, bases, & teeth.
     Factors influencing the RPD Design




7. Patient’s past experience, i.e., patient’s inability to accept
         lingual bar or palatal bar major connector.
      Factors influencing the RPD Design




8. Replacing a single tooth or anterior teeth – RPD or FPD.
             Difference between two types of RPDs




                Tooth Supported    Tooth & tissue Supported
                  class III & IV          class I & II
1. Support       Abutment teeth    Combination of abutment teeth
                                   and soft tissues.
           Difference between two types of RPDs




                Tooth Supported      Tooth & tissue Supported
                  class III & IV            class I & II
2. Impression    Anatomic form     Anatomic and functional forms
                                      (altered cast technique).
          Difference between two types of RPDs




                Tooth Supported        Tooth & tissue Supported
                  class III & IV              class I & II

3. Indirect    No denture rotation   Needed to resist any denture base
   Retention   hence, not needed     lifting away from the tissues.
         Difference between two types of RPDs




                Tooth Supported         Tooth & tissue Supported
                  class III & IV               class I & II
4. Base type   Metal base – no future   Acrylic base – future reline is
               reline is required.      anticipated due to bone loss.
         Difference between two types of RPDs




                 Tooth Supported         Tooth & tissue Supported
                   class III & IV               class I & II
5. Clasp design Circlet/Embrasure/Ring Stress release design – RPI /
                ‘No stress release’     RPC, - wrought wire clasp.
Components of an RPD Framework
              (Review)

       Circumferential Clasps
      Circlet / conventional / C clasp
      Embrasure clasp
      Reverse action / Hairpin clasp
      Ring clasp
      Multiple clasp
      Half & half clasp
      Combination clasp
Components of an RPD Framework
              (Review)

    Infra Bulge or Bar type Clasps
              1. T – bar
              2. Y – bar
              3. L – bar
              4. I – bar
system
    Factors for the Choice of a Direct Retainer

1. The type of an RPD:
   a. tooth supported:- any type of clasp can be used.
   b. tooth-tissue supported:- stress releasing (I bar) is used.
2. The location of the undercut on the abutment tooth in relation to
   the saddle area (circlet / ring / hairpin).
3. The periodontal health of abutment (cast / wrought clasp).
4. The size of an abutment tooth (cast / wrought clasp).
5. The presence of a tissue undercut – combination clasp.
6. Esthetic considerations – I bar clasp in the distal undercut or
   circlet clasp in the mesial undercut on anterior abutment.
 Components of an RPD Framework
                  (Review)
        Maxillary Major Connectors

1. Single Palatal Bar
2. Single Palatal Strap
3. U – shaped Palatal Connector
4. Anterior & Posterior Palatal Straps / Bars
5. Palatal Plate
          Factors for the Choice of a Maxillary
                   Major Connector
The rigidity and location in relation to the gingivae and the
    vibrating line posteriorly is critical.
 1. Its design depends on the number and location of the saddle
      areas and emerges finally after connecting them together, e.g.,
      modified palatal strap or anterior – posterior palatal straps major
      connectors.
 2. Single palatal bar and U – shaped connectors are seldom used.
      The later design may be used in the presence of a large palatal
      torus.
Components of an RPD Framework
              (Review)
   Mandibular Major Connectors

      1. Lingual Bar
      2. Lingual Plate
      2b.Interrupted Lingual Plate
      3. Double Lingual Bar
      4. Labial Bar
    Factors for the Choice of a Mandibular
                    Major Connector

It must be rigid and properly located in relation to the
   gingivae and movable oral tissues.
  1. Depth of anterior lingual sulcus (8 mm or less).
  2. Periodontal health of the anterior teeth (bar or plate).
  3. Class I edentulous arch may necessitate lingual plate
     for additional resistance to horizontal rotation.
  4. Anterior spacing (interrupted plate or Continuous bar).
Components of an RPD Framework
                  (Review)

Posterior Rest Seats

 1. Occlusal rest.
 2. Long occlusal rest.
 3. Embrasure rest.
 4. Onlay/overlay rest.
Components of an RPD Framework
                    (Review)

   Anterior rest seats
1. Cingulum / inverted V rest.
2. Ledge rest.
3. Ball rest.
4. Incisal rest.
             Selection of a Denture Base
                           Types:
               1. Metal base (class III & IV).
             2. Acrylic resin base (class I & II)
      The single important factor in the design of a saddle area and
for the choice of a denture base material is the anticipated need for
future reline. As class I & II RPDs may require future reline of the
saddle areas (to compensate for the bone loss due to the rotational
movement occurring under occlusal load), an acrylic resin denture
base in indicated.
               Step by Step Procedure to Design

        As a start, guiding planes should be marked on the proximal
  surfaces of the abutment teeth adjacent to the saddle areas, according
  to the selected path of insertion.

Step 1: Plan Tooth Support
  For bounded saddles, place the
  prepared rest seats on the occlusal,
  cingulum, or incisal surfaces of the
  abutment teeth, near the edentulous
  areas.
  For distal extension saddle areas,
  the rest seats are placed on the mesial
  side of the abutment, i.e., away from the saddle areas.
               Step by Step Procedure to Design
Step 2: Design & Locate the Connectors.
       The final shape and form of the palatal major connector
  develops after connecting the tooth supported and tooth-tissue
  supported units of the arch together.
  The choice of a mandibular major
  connector, however, depends on the
  depth of the anterior lingual sulcus.

  The minor connectors will then be
  placed to connect other parts of the
  RPD (rests, retainers, artificial
  teeth, etc..) to the major connector.
                  Step by Step Procedure to Design
Step 3: Plan Retention:
         Ideally, a direct retainer should be placed on either side of the
   saddle area. Its location on the tooth is dependent on the presence of
   a suitable undercut – 0.01”. A bracing or
   reciprocal arm should also be included.

   For a distal extension saddle, an I-bar
   retainer is preferred, as a part of RPI.
   This design should also include an
    indirect retainer to minimize rotation
   of the denture base away from the
   tissues.
                  Step by Step Procedure to Design
Step 4: Connect retainers to the support units:
         Supra-bulge clasp is connected to the occlusal rest or the
   guiding plate. Infra bulge clasp is connected to the mesh work minor
   connector in the denture base.


Step 5: Outline and join the saddle areas
   (denture base) to these selected or
   drawn components of the RPD
   framework.
                Designing Mandibular Framework
            Check List
   Locate Guide planes – POI.
   Plan Support.
   Select the major connector.
   Place the minor connectors for
    occlusal rests, clasps, artificial
    teeth.
   Plan retention (direct & Indirect).
   Connect the retainers to the
    framework components.
   Outline and connect the saddle
    areas to the major connector.

								
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