RPD week 4
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♦ What are the types of rests for anterior teeth?
- Cingulum rests
- •Incisal rests
- •Circular concave rests
♦ What is the type of anterior rests most commonly used for maxillary canines?
♦ How do you prepare the positive incisal rest seats?
- mandibular anteriors
- 1/3-1/2 width of incisal edge and sufficient clearance
- Concave rest seat mesiodistally
- Convex rest seat buccolingually
- May create greater leverage on the tooth compare to cingulum rests when used improperly and is only used when the lingual anatomy of the tooth is not appropriate
♦ What are the roles of proximal plates?
- 1. Maintains arch integrity by producing bracing action.
- 2. Acts as retainers by frictional contact with the parallel guide planes on the teeth.
- 3. Guide a partial to seat along the path of insertion.
- 4. Provides reciprocation to a retainer
- 5. Protect against food impaction and tissue hypertrophy by adapting the guide plane at the tooth-tissue junction.
- 6. Facilitate a self-cleansing effect compared to the acrylic
- ♦ What must be considered to maintain the health in the area between soft tissue and abutment?
- 1. Impaction of food into the space.
- 2. Hypertrophy of tissue into the space.
- 3. A reduced bracing effect between the remaining teeth.
- 4. Increased periodontal involvement.
♦ What are the infrabulge and suprabulge retainers? Name representative retainers in each of the types?
- Infrabulge (I-bar)
- Suprabulge (C-clasp)
♦ What are the advantages of I-bar retainers over the C-clasp retainers?
- Minimal tooth contact
- Minimal interference with natural tooth contour.
- Maximum natural cleansing action.
- Reduced display of metal for better esthetics.
- Passive functional movement on the abutment adjacent to an extension-base
♦ What are the requirements to design the I-bar retainer?
- To originate at a gingival area and cross the tooth-tissue junction at right angles.
- To engage an undercut 0.01 inch or 0.25 mm. The
- abutment needs to have the undercut around the
- The tip of the I-bar should be located ideally within the cervical 1/3 or could be lower than the cervical ½.
- The retention area should be at least 1 mm above the gingival margin
- To extend in a straight line down (5-7mm) to create
- sufficient flexibility; therefore, severe soft tissue undercut is a contraindication of I-bar Above the height of contour of the soft tissue
- When no undercut found, a retentive area, or a dimple, can be created by a round bur, with an
- approximately 1.5 mm diameter and an adequate depth depending on the contour of the abutment.
- To be reciprocated by one of the following 3 structures:
- (1) a combination of a proximal plate and minor connector, Passive Active
- (2) a passive retainer, or
- (3) a plate.
Proximal Plates (a metal structure facing a guide plane): Fundamentals in guide plane preparation
- 1. The larger, the better bracing.
- 2. Curvilinear prep within the enamel.
- 3. Therefore, they can not always be prepared fully to the gingiva.
- 4. Preserve facial anatomy in the esthetic zone.
- 5. The more parallel each other, the more retention can be generated.
- 6. The more parallel each other, the longer bracing and retention last.
Which is first to prep, rests or guide planes ?
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