DL-216 Lecture Notes: Removable Partial Denture,

Topic1: Classification & Components

 

(1) Definitions and Functions

(2) General Construction Characteristics

(3) Construction Requirements

(4) Kennedy classifications

(5) Connectors

(6) Rests

(7) Retainers

(8) Denture Bases

 

  1. Definitions and Purpose
    1. Clasp Retained Removable Partial Denture
      1. A removable prosthesis replacing one or more of the natural teeth and their associated structures (gingival tissue, supporting bone, etc.)
      2. The condition being that one or more natural teeth still remain
      3. Supported by the teeth or the teeth and mucosa
      4. Retained in a functional position by clasps
    2. Abutment tooth - A natural tooth specifically used for direct retention or for support purposes
      1. Desirable undercut: A zone of undercut that has sufficient depth, suitable location and reasonable accessibility needed for RPD retention
      2. Undesirable undercuts: All tooth and soft tissue undercuts along the path of insertion which the rigid parts of the RPD must not contact when going into place
    3. Purpose of RPD
      1. Restore the patient's natural appearance (esthetics)
      2. Restore function without damaging the remaining natural teeth and tissues

     

  2. General Construction Characteristics
    1. All acrylic
      1. Intended to be temporary
      2. Called "interim" or "treatment" RPD
      3. May include wire clasps
    2. All metal (chrome nickel, chrome cobalt, gold or titanium)
      1. Used for posterior tooth replacement where esthetics are unimportant
      2. For nickel sensitive patients chrome cobalt, gold or titanium may be used
    3. Combination
      1. metal frame to which denture acrylic and artificial teeth are attached
      2. the most common variety

 

(3) Clinical Procedures

 

    1. Patient presents with missing natural dentition.
    2. Impression taken for diagnostic cast.
    3. Dentist does preliminary design for R.P.D.

      Determines path of insertion.

      Need-for and placement of rests and clasps.

      Custom tray is made if desired.

    4. Custom tray Fabrication
    5. Similar to other custom trays.

      Baseplate wax is formed over cast for uniform spacing.

      Tissue stops are cut out of baseplate wax.

      Tray material is formed over cast.

    6. Dentist prepares teeth if necessary
    7. Rest preparations

      Guide plains

      Dimples for retention.

    8. Final Impression is taken.

Impression is disinfected.

Master cast is poured.

Design may or may not be transferred to Master Cast.

Master Cast is sent to Laboratory for R.P.D. fabrication.

 

  1. Construction Requirements
    1. If an RPD is to serve its stated purpose, it must be
      1. Retained - not fall out
      2. Supported - not impinge (smash) the tissue of the mouth it covers
      3. Braced - not shift around front to back or from side to side
    2. RPDs are, to a large extent, retained, supported, and braced by remaining natural teeth

     

  2. Kennedy classifications
    1. Class I
      1. Bilateral edentulous areas posterior to the remaining teeth
      2. Also known as bilateral distal extension
      3. Extension - supported by the natural teeth and residual ridge
    2. Class II
      1. Unilateral edentulous area posterior to the remaining natural teeth
      2. Also known as unilateral distal extension
    3. Class III
      1. A unilateral edentulous area with natural teeth anterior and posterior to it
      2. Also known as toothborne - supported by remaining natural teeth only
    4. Class IV
      1. A single, but bilateral (crossing the midline), edentulous area anterior to the remaining natural teeth
      2. Also known as anterior extension
    5. Rules for Kennedy classification
      1. The most posterior edentulous area to be replaced always determines the classification
      2. Other edentulous areas are modifications and designated by their number
      3. The extent of the modification is not considered, only the number of additional edentulous areas
      4. There can be no modifications in Class IV arches

     

     

  3. Connectors - The parts of a partial denture framework that joins various components together
    1. Major Connector
      1. Function
        1. Joins one side of the framework to the other
        2. Distributes stresses across the arch
        3. Counteracts tipping forces during mastication
      2. Maxillary Major Connectors
        1. Palatal strap
        2. Anterior-Posterior palatal bar or strap
        3. Horseshoe
        4. Closed horseshoe
        5. Full palatal coverage
      3. Mandibular Major Connectors
        1. Lingual bar - Most commonly used of the mandibular major connectors
        2. Double lingual bar- lingual bar and Kennedy bar
        3. Lingual plate - where lingual bar is not practical. Also known as the closed Kennedy bar
        4. Labial bar - when undercuts prohibit use of lingual bar or plate
    2. Minor connectors - Connects the major connectors to other components
  4. Rests
    1. The components which prevent the RPD from placing pressure on the soft tissues of mouth
    2. Serve primarily to transfer forces occurring against the prosthesis down the long axis of the abutment teeth
    3. constructed to fit into the rest seats on the abutment teeth
    4. Types of rests
      1. Occlusal rest - made to fit a rest seat on bicuspids and molars
      2. Incisal rest - usually located on the incisal edge of lower anterior teeth
      3. Lingual rest - fits into seat prepared on the cingulum of upper or lower anterior teeth (usually cuspids)
    5. All rests must be thick enough to withstand chewing forces without breaking; no less than 1mm thick

     

  5. Retainers - prevent displacement of the framework during function
    1. Direct Retainer (clasps)
      1. Grasps an abutment tooth to resist movement (removal) in an occlusal direction
      2. Requirements of a Clasp Assembly
        1. Retention
          1. Resistance to dislodgment in an occlusal direction
          2. Provided by the clasp tip engaging the undercut when a dislodging force is applied
        2. Reciprocation
          1. Force on a tooth must be offset by an opposite and equal force (balancing)
          2. Must contact tooth at same time as clasp on insertion
        3. Bracing (Stabilize)
          1. Resistance to forces from a lateral (sideways) and anterior posterior direction
          2. Provided by the arms and occlusal rest
        4. Support
          1. Resistance to displacement in a gingival direction
          2. Provided principally by the rests
        5. Encirclement
          1. Must encircle at least 180 degrees of the tooth
          2. Prevents the tooth from moving out of the clasp
        6. Passivity
          1. When a clasp is in place on a tooth, it should be at rest
          2. Its retentive function is activated only when dislodging forces are applied
      3. Basic Clasp Classifications
        1. Circumferential clasp
          1. The clasp arm approaches the undercut from above the survey line
          2. Easiest clasp to make
          3. Easiest clasp to adjust
          4. Sometimes referred to as:
            1. "C" clasp
            2. Akers clasp
            3. Suprabulge clasp
          5. Types of circumferential clasps
            1. Simple circumferential - most versatile of all clasps and most universally used
            2. Embrasure clasp - used in a quadrant of the mouth where there is not an edentulous area
        2. Bar Clasp
          1. The approach arm approaches the undercut from below the survey line
          2. More esthetic
          3. Harder to adjust
          4. Sometimes referred to as:
            1. Roach clasp
            2. Infrabulge clasp
          5. Types of bar clasps
            1. "T" clasp
            2. Modified "T" clasp - more esthetic than "T" clasp, referred to as 1/2 "T"
            3. "I" bar - used where esthetics is the prime consideration
      4. Parts of a Clasp Assembly
        1. Minor connector - connects clasp assembly to the major connector
        2. Body - the junction of the shoulder, clasp arm, rest, and minor connector
        3. Occlusal Rest - supports the partial against downward (vertical) forces
        4. Clasp arm(s)
          1. Shoulder
            1. The proximal 1/3
            2. Non flexible
          2. Retentive tip
            1. The terminal 1/3
            2. Flexible portion
            3. Engages desirable undercut
          3. Reciprocal Arm/Plate
            1. Offsets forces exerted by the retentive arm
            2. Non flexible
          4. Approach Arm - on bar type clasps only
      5. Rules for Clasp Construction
        1. Flexibility
          1. Increased by curving, thus lengthening the retentive arm
          2. Doubling the length of the retentive arm quadruples the flexibility
        2. Uniform Taper
          1. Absolutely essential for the arms of a "C" clasp or the approach arm of a bar clasp
          2. Clasp should be one-half the thickness at the tip than it is at the attachment to the body
          3. A tapered clasp arm will have twice the flexibility compared to one not tapered
          4. No thick or thin spots in the clasp arms
          5. Clasp arms which cross a groove on a tooth should be dipped in on their outer surface in order to maintain a uniform thickness
      6. Clasp types
        1. Cast metal - Fabricated using wax or plastic patterns
        2. Wrought wire
          1. Commercially supplied wire of various gauges
          2. Adapted to cast by bending with pliers
    2. Indirect retainers
      1. A part of a removable partial denture framework located on the opposite side of the fulcrum line from tipping forces; designed to counteract those forces
      2. Distal extensions create most tipping forces
      3. May be auxiliary rests, part of a clasp assembly, lingual rests under lingual plating, or major connector

     

  6. Denture Bases
    1. Acrylic Resin
      1. Most commonly used material for RPD denture base construction
      2. Mechanical retention provided by
        1. Mesh
        2. Bar (Open)
        3. Beads
    2. Metal- used on well healed edentulous areas where very little or no resorption is expected to occur

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