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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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