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List the basic principles of partial denture design.
- Major connectors must be rigid.
- Occlusal rest must direct occlusal forces along the long axis of the teeth.
- Guide planes are employed to enhance stability and bracing.
- Retention must be within the limits of physiologic tolerance of the periodontal ligament.
- Maximum support is gained from the adjacent soft tissue denture bearing surfaces.
- Designs must consider the needs of cleansibility.
- The RPD must achieve retention, stability and support via the following.
- The rests must be positive and direct functional forces in the long axis of the tooth and as close to the center of the tooth as possible.
- The Major connectors must be rigid in order to achieve cross arch stabilization and must be in intimate contact to soft tissues in order to promote cleansibility.
- Parallel guiding surfaces allow for passive insertion and bracing utilizing proximal plates.
- Reciprocation is achieved utilizing minor connectors, proximal plates and retainers.
- Undue stress to PDL should be minimized w/ rest design and the RPD must not actively engage the dentition in function.
- Soft tissue support in adjacent edentulous areas maximizes support.
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List the 6 requirements of a clasp
- 1. Retention
- 2. Bracing
- 3. Support
- 4. Reciprocation
- 5. Encirclement of the tooth over 180 degrees
- 6. Passivisity
- 1. Minimal tooth contact
- 2. Exact placement of retention contact
- 3. Minimal interference with natural tooth contour
- 4. Maximum natural cleansing action
- 5. Passive functional movement of an extension prosthesis
- 6. Reduced display of metal, for better esthetics
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Crowns are necessary as RPD abutments to:
- 1. establish the proper guide plane if abutment has previous crown
- 2. reposition the clinical crown
- 3. restore a badly broken down clinical crown
- 4. also, a proper rest could be incorporated into the crown which is not normally present on the tooth, such as a cingulum rest on a mandibular canine
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Name the three types of “positive” rests that can be used on anterior abutments.
- 3 types of positive anterior rests:
- 1. incisal
- 2. circular concave
- 3. cingulum
- (1)Cingulum rest –
- a. Crescent-shaped
- b. As center as possible when viewed from all directions
- c.The center is deeper buccal-lingually (positive rest)
- (2)Insisal rest- concave mesiodistally and convex buccolabially.
- (3)Circular concave
- a) circular concave rest
- i. #2 or #4 round bur
- b) incisal rest
- i. two planes preparation with flame shaped bur
- 1. incisal plane
- 2. labial plane
- ii. concave mesiodistally, convex buccolingually
- iii. 1/3 of mesiodistal incisal width
- c) cingulum rest
- i. flamed shape and inverted cone shape burs
- 1. use flamed shape bur at 45 to create an outline form
- 2. use inverted cone shape bur to create positive rest seat
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What type of suprabulge retainer do we recommend at UCLA? Why? When do we recommend that such a retainer be used?
- Recommendation: Circumferential Clasp (aka: Akers Clasp) because
- i. With flexible retentive arm that crosses the height of contour into the undercut and a rigid reciprocating arm that stays above the height of contour
- ii. Fulfills the requirements of clasp
- 1. Retention
- 2. Bracing
- 3. Support
- 4. Reciprocation
- 5. Encirclement
- 6. Passivity
- Indications for use of a circumferential clasp
- b. Bulbous gingival contours
- c. Lack of access for an I-bar clasp due to a shallow vestibule, a frenum attachment, or a severe gingival undercut
- d. Short teeth with poor or no guide planes
- e. Tilted teeth
- f. Significant recession and/or abfraction
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