Clinic 1 - RxDentistry

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Clinic 1 - RxDentistry Powered By Docstoc
					Introduction to Clinical
Prosthodontics
• Clinic 1. History taking, examination,
  treatment planning, and Primary
  Impressions.
    – Lab1. SM & custom trays.
• Clinic 2. Secondary/master/final
  impressions.
    – Lab 2. Secondary/master/final casts
      & occlusal wax rims (record blocks)
• Clinic 3. Registration stage:
    1. Aesthetics (maxillary wax rim)
    2. Vertical (VD) & horizontal (RCP)
       relations.
    3. Shade & Mould.
    – Lab3. : Mounting teeth arrangement
       (setting)
• Clinic 4. Try in
    – Repetition of previous visit.
    – Post dam determination.
    – Lab 4.: denture processing: flasking,
      dewaxing, packing, curing,
      deflasking, finishing and polishing.
• Clinic 5. Insertion
• Clinic 6. Review
                         Clinic 1
   Primary Impression-summary of the
    anatomical extent:
       Maxillary:
          Residual ridges, tuberosities and hamular notches,
           functional width and depth of the labial and buccal
           sulci, including frena.
          Hard palate and its junction with the soft palate.

       Mandibular:
          Residual ridges and retromolar pads.
          Functional labial and buccal sulci (including frenal
           and external oblique ridges)
          Lingual sulci, lingual frenum, mylohyoid ridges and
           retromylohyoid areas.
   Mucous membrane
       Mucosa: stratified squamus epithelium & connective
        tissue (lamina propria)
       Submucosa: connective tissues made of dens to loose
        areolar tissues
            If firmly attached: withstand pressure
            If loose, thin, traumatized, mobile, flappy: it wont be suitable
             to withstand pressure-not resilient.
   Masticatory mucosa (keratinized): hard palate,
   Hard palate
       Keratinized.
       Mid palatine suture: Submucosa is extremely thin-
        requires relief
       Horizontal portion of the Hard palate: 1 support for
        areas
       Rugae areas: set at an angle with the residual ridge-
        2 support areas.
   The Palatal Gingival Vestige (remnants of
    the lingual gingival margin)
   It is the remains of the palatal gingiva. After
    tooth extraction the position of the vestige
    remains relatively constant, the same as the
    incisive papilla. This can be a very helpful
    pointer for posterior tooth positioning during
    denture construction
   Residual Ridges
       Mucous membrane:
          keratinized
          firmly attached.

          Submucosa: devoid of glandular tissues. Dense
           collagenous fibers. Relatively thin, but sufficient to
           provide support for the denture base.
       Crest of the ridge:
          Prone to resorption.
          2 support area.

       Inclined facial surfaces
          Loses it’s firm attachment
          Offers little support

          Cannot withstand pressure
   Two orifices one each side of the midline.
    Coalescence of several mucous glands - always
    located in the soft palate. They act as collecting
    ducts for a group of minor palatine salivary
    glands
   Imaginary line.
   Usually 2mm in front of the fovea palatine
   Not the junction of the hard and soft palate-
    always on the soft palate.
   Submucosa
       Glandular tissues-because it is not supported by
        bone, it could be compressed and relocated with the
        impression to complete the palatal seal.
   Crest of the residual ridge
       Ridge is similar to that of the upper in healthy
        mouth.
       Attachment varies considerably. In some
        people, the submucosa is loosely attached to
        the bone.
       When securely attached to the bone, the
        mucous membrane is capable of providing
        support for the denture. However, because
        underlying bone is cancelous, the crest of the
        residual ridge may be not favorable as a
        primary stress bearing area for the lower
        denture.
   Buccal shelf area
       The mucous membrane is more loosely attached and
        less keratinized than that covering the residual ridge.
        Although the mucous membrane may not be as
        suitable histological to provide support for the
        denture, the bone of the buccal shelf area is covered
        by a layer of cortical bone. This plus the fact that the
        shelf lies at right angle to the vertical occlusal forces,
        makes it the most suitable primary stress bearing
   The external oblique ridge does not govern the extension of the
    buccal flange because the resistance or lack of it varies widely. The
    buccal flange may extend to the external oblique ridge, up onto it or
    even over it depending on the location of the muco buccal fold.
   The bearing of the denture on muscle fiber of the buccinator would
    not be possible except for the fact that the fibers run parallel to the
    base, and ,hence , its action is parallel to the border and not at right
    angle.
   The disto buccal border must converge rapidly to avoid the action of the
    masseter which is pushing inward the buccinator.
   Distal extension is limited by
        Ramus
        Buccinator
        Pterygo mandibular raph.
        Superior constrictor
        The sharpness of the boundaries of the retromolar
         fossa. (the denture should extend slightly to the
         lingual into the pearl shaped retro molar pad.
   The retro molar pad is a triangular soft pad of
    tissue. Its mucosa is composed of thin non
    keratinized epithelium. It submucosa contains
       Glandular tissues
       Fibers of the buccinator and superior constrictor
       Pterygo mandibular raph
       Fibers of the temporalis
   Because of theses structures, the denture base
    should only extend to one half to two third the
    retro molar pad.
   The retro molar pad:
   It is split into two sections. The anterior section is usually firm and
    fibrous. It is important for denture support and preventing distal
    denture displacement

   The mylohyoid ridge:
   Following the extraction of natural teeth and subsequent resorption,
    the mylohyoid ridge becomes more prominent. This can result in
    mucosal soreness beneath the denture bearing area over the
    mylohyoid ridge.

   Mylohyoid muscle
       It is a thin sheet of fibers and in a relaxed
        state will not resist the impression material.
       Carrying the border under the mylohyoid
        cannot be tolerated. The contraction of this
        muscle will displace the denture.
       Fortunately, the denture in the posterior area
        of the mylohyoid is beyond its attachment
        because the mucobuccal fold is not in this
        area.
       In the retro mylohyoid fossa the border of the
        denture move back toward the body of the
        mandible producing the S curve of the lingual
        flange.
       In the anterior region, a depression, the pre
                Clinic 1
     Making the Primary Impression
   Selection of the impression tray
        impression trays are rigid containers used to
        carry the impression material into the mouth.
        They also support it while it sets or harden,
        and subsequently during removal from the
        mouth and when casts are poured.
       Wide selection is available in metal or plastic.
       Selection is based on:
          Rigidity
          The need to accommodate an appropriate amount
           of the impression material.
          The design or extent of the tray to the anatomical
           landmarks outlined previously.
   Metal trays:
       Rigid
       Provided in a wider range of sizes.
       Needed to be cleaned and sterilized before reuse.
   Plastic trays are intended to be disposable
   Impression materials:
       Alginate
       Compound
       Rubber
   Check that the tray is not over extended or under
    extended. Then load the impression material and make
    the mandibular impression standing in front of the
    patient. For the maxillary impression, the clinician should
    be positioned behind the patient. As this affords more
    control over the upper tray and also allow the patient’s
    head to be leaned forward should they experienced
    nausea during the impression procedure.
   Inadequate final impression: contact clinician to discuss
    possible risks of proceeding with the case




  Model fractures upon removal from impression.
 Large positive or negative defects, or flaws in critical areas.
Poor surface quality of the model due to water/saliva/blood
  contamination or improper mixing of gypsum, showing a
  powdery, friable surface.
 Loss of or damage to critical areas during model trimming
  (examples: retromolar pad, hamular notch and muscle
  attachments).
Lab 1
Producing Casts & Special Trays
• Ensure that impressions have been decontaminated prior to dispatch
  to the lab.
• Preparing the primary cast:
   – Principally used to provide bases on which
     customized special trays are constructed.
   – Also useful for planning treatment, for example for
     outlining the potential supporting areas of the
     denture.
   – Cast are made in Plaster of Paris ( β hemihydrate
     of calcium sulphate) & Stone (α- hemihydrate of
     calcium sulphate).
   – Pour using 50:50 mixture of plaster of Paris/ dental
     stone (vacuum mixed) under vibration.
   – Make the base at least 10mm thick to be
     sufficiently robust to survive subsequent handling.
• Powder/liquid ratio
    – Thin mix: longer setting time, poor surface
      hardening, setting expansion is low, easier to pour.
    – Thick mix: the opposite.
• Spatulation time: time taken to mix the powder &
  liquid into creamy consistency.(30-60 sec.)
Increasing the spatulation time:
    – Rapid set.
    – Decreases surface hardness.
    – Increases the setting expansion.
• Temperature: water temp. up to 40 cº decreases
  setting, above 40 cº increases setting.
• Chemical additives. E.g. Borax increases setting time.
•   Read the prescription before beginning all procedures.
•   Box master model impressions- Diagnostic casts do not require
    boxing.




•    Measure dental stone and water according to manufacturer's
    directions.
•   Add powder to water rather than water to powder. For best
    results, vacuum mixing is recommended.
•   Do not invert impressions to develop a base until the stone
    reaches initial set.
                 Master casts
• Base thickness must be 1/2-inch (13 mm)
  minimum for strength. This is measured from
  the deepest part of the palate on the upper
  (Figure 1c) or the "floor of the mouth" on the
  lower (Figure 1d).
• After trimming, the base of the
  model must be parallel to the
  residual ridge (figures 1e and
  1f).
• The base must be indexed for
  mounting and remounting. Two
  methods are shown here. Other
  techniques are acceptable as
  long as the index allows
  accurate remounting of the
  model.
• The depth of the buccal sulcus is approximately 1-1.5-
  mm below the land area. Positive defects (bubbles), if
  any, must be in non-vital areas and small enough to
  be easily removed (1-mm diameter or less as a guide).
• Negative defects (voids), if any, should be small and in
  non-critical areas. These should be filled with stone to
  blend with the surrounding anatomy.
• The master cast must include all anatomical surfaces
  in the final impression.
       Special Trays
• Material:
   – Should be safe to handle, compatible with
     biological tissues & impression material, sufficiently
     rigid to preclude distortion.
   – Examples: Self-cured or light-cured acrylic resin
• Peripheral extension:
   – Cover the entire denture-bearing area within the
     anatomical limits previously described.
   – 2mm short of the sulcus to allow for border molding.
• Handles:
   – Should be formed to avoid encroaching on the
     surrounding tissues.
• Space for impression material:
  – Should accommodate the optimum thickness of
    the chosen impression material
     • Irreversible Hydrocolloid: 3mm.
     • Zinc oxide-eugenol : close fitting
     • Poly vinyl siloxanes: depending on the viscosity
     • Polyethers : 2-3mm
     • Polysulphides: 2-3mm.
• Perforations??
  – Trays for complete dentures are requested without
    perforations so that peripheral seal can be
    estimated.
•   If no specific instructions are provided,
    fabricate tray to the following standard: Outline
    the tray 1-2 mm short of the mucobuccal reflection for both
    upper and lower models. This will allow room for border
    moulding material and save time for the clinician. The tray
    must extend to the depth of the hamular notches on the upper
    and should cover the retromolar pads on the lower . The lingual
    extension on the lower should stop at the mylohyoid line in the
    posterior and at the junction with the floor of the mouth in the
    anterior section.
•   Place relief material such as baseplate wax
    to the outlined area and cut out three tissue
    stops. Avoid placing a tissue stop over the
    incisive papilla.
•   The maxillary tray is made with 1 mm wax spacer and ends
    short of the final tray extensions. On the maxilla, wax must not
    cover the posterior palatal seal area. The mandibular tray is
    made with no spacer(close fit)
•   Tray is well adapted to the model with no voids.
•   Tray must be of uniform thickness.
•   Thickness must be sufficient in strength to prevent distortion or
    breakage in use. The required thickness will vary with the
    material used. In general, acrylic resin and similar materials
    (such as light cure resins) should be approximately 2 mm thick,
    and 1 mm short of the mucobuccal fold to allow for border
    moulding.
•   The handle must be placed in the anterior so that it does not
    interfere with placement of tray or border moulding
    procedures. The handle may be placed approximately where
    the wax rim or anterior teeth would be positioned on a
    baseplate .
•   Unless specified otherwise by the clinician, the tray borders
    should be between 1 to 2 mm short of the mucobuccal
    reflection.
               Custom Trays - Quality Failures
•   Border extensions significantly longer or shorter than
    standard.
•   Tray not stable (flexible) due to insufficient thickness.
•   Tray cracked or damaged.
•   Improper handle position (interferes with border
    moulding or insertion).
•   Sharp and/or rough edges, which may irritate the
    patient.
        Clinic 2
Definitive (secondary)
     Impression
Classification: Elasticity
Lab 2
Base plates & Wax rims
• Master/secondary
  cast (poured in
  stone)
• Base plate:
  – Self-cured or light-
    cured acrylic resin.
  – Wax rim
• (review lecture: Base
  plates & Waxrims/3rd
  year course)
                   Clinic 3
              Registration Stage
   Before complete dentures are constructed, the dentist
    with the aid of the technician, must build a pro-forma or
    template of the intended denture using-usually- wax
    rims.
   According to glossary of prosthodontic terms the
    registration is ‘a record made of the desired
    maxillomandibular relationship and is used to relate
    casts on the articulator’
   Maxillomandibular relationship is ‘ a relationship of the
    maxilla to the mandible; any one of the infinite
    relationships of the mandible to the maxilla’
   In simple terms: the registration stage is 3-dimensional
    prescription whereby the template of the intended
    denture is ‘prescribed and fashioned’ clinically before
    being dispatched to the laboratory for placement of the
    teeth on the trial denture.
   Unless the clinician has cast the definitive impression
    and has scored the master cast to define the postdam,
    the rim will not exhibit a clinically meaningful seal.
   After immersing the rim in proper disinfectant material,
    ensure that the rim is well adapted. Alternating finger
    pressure on both sides of each rim should not elicit
    rocking.
   Start with the upper rim- insert it and then ensure that
    the infra-nasal tissues are harmonious with the soft
    tissues of the middle third of the face. Failure to do so
    may affect the form and length of the upper lip.
   Confirm that the upper lip is adequately supported. This
    should result in restoration of the vermilion border.
   Determine the level of the incisal point relative to the
    resting upper lip. Some text books recommend 2mm
    below the resting upper lip level. Younger patients with
    class II div I may require more(2-4mm) and older
    patient ( over 70) may require the incisal level at the
    level of the resting lip or 1mm above it.
   The antero-posterior location of the incisal point can be determined by
    asking the patient to say a word containing a fricative consonant, e.g. ‘fish’.
    The incisal point should correspond to the vermilion border of the lower lip.
   Determining the maxillary anterior & posterior plan:
       The plan of the six anterior should be parallel to the inter-pupillary line.
        Use a fox’s occlusal plane guide.
       The posterior plan should be made parallel to ala- tragus line
   The tips of the maxillary canines can be determined by extending a dental
    floss from the inner canthus of the eye through the lateral border of alar
    cartilage into the rim.
   Using the mark on the rim corresponding to the canine tips, reduce the
    inferior borders of the posterior rims by 3-5 ° to create the buccal corridors.
   The customization of the upper rim is finished by scribing
       Centre line.
       High smile line
       Canine points
   The above technique of customizing the upper rim is the one used at the
    Dental Health centre-the one to be used by dental student. Another
    technique to customize the upper rim is Swissedent technique (review
    lecture on wax rims /3rd year).
   Face bow transfer : depending on the case, the clinician may consider it
    necessary to use a face-bow to transfer the relationship of the upper rim to
    an arbitrary hinge axis. although it may not be strictly necessary to use a
    face- bow in all cases, there is no valid objection to their use in the
    prescription of complete denture.
Clinic 3
Clinic 3
   Relating the mandible to the maxilla
       This 3-dimensional:
          Vertical (vertical dimension)
          Sagital ( antero-posterior)

          Coronal (left –right)

   Vertical:
       Resting Vertical Dimension (RVD)
       Occlusal Vertical Dimension (OVD)
            Affect tolerance and appearance
       Free way space (RVD-OVD)
   RVD measurement:
       Select to measuring points in the midline of
        the face-one relate to the nose and one to
        the chin. These points must be on sites with
        minimal influence from the muscles.
       Ask the patient to moisten his or her lip and
        bring them into light contact, then ask the
        patient to swallow and relax his jaws
           This is verified by asking the patient to
             say the word ‘M’ while the
             measurement is made.
           Attention should be made to unwanted
             skin movement. Use Willis gouge or
             any other device-ruler- to measure the
             distance between the two reference
             points. This the RVD.
           The maxillary & mandibular rims are
             then inserted-after the upper rim has
             been moulded- and the lower rim is
             reduced in height- usually; or added to
             if under sized) until it contacts the
             upper rim evenly at a vertical
             dimension of occlusion some 2-4mm
             less than RVD
methods of determining vertical
         dimension
-1. Boos: Bimeter (an oral meter that
measures pressure)
-2. Silverman: closest speaking space-
looked at bicuspid area
-3. Pound: phonetics and esthetics
-4. Lytle: neuromuscular perception
-5. Pleasure: pleasure points (tip of nose
and chin)
         Sagittal (antero-posterior)
   Retruded Contact Position
    (RCP)
        Reporduciple
   Several techniques:
        Squash bite
        Wax rims
        Intra-oral tracing
   This visit is finished by
        selecting the shade
         and mould.
        determining the post
         dam area.
Selection of the mould & shade
Facebow transfer of the maxillary
             rim
Facebow transfer
Lab 3

• Mounting. (indexing)
• Setting the teeth
  using the shade &
  mould selected by
  the dentist.
• Wax up and
  contouring.
  (hands out
  summarizing this
  laboratory
  procedures will be
  given)
                   Clinic 4
                  try-in visit
   Verify the appearance.
   Verify the occlusal requirements.
   Examine speech

( Please review lecture : try-in /3rd year)
Lab 4
Flasking, Packing and
finishing& processing of
• Packing
 the denture:
  1. Removal of wax
  2. Replacing the wax mould
     with PMMA
  (hands- out summarizing this
     laboratory procedures will be
     given)
                   Clinic 5
                 Fit /Delivery
 Mirror those of the trial stage except
  hopefully the patient is taking the
  dentures home.
(review lecture on denture insertion/ 3rd
  year)
   Arrange review visits for your patient as
    needed.

				
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