Rest Seats Flashcards
What is a rest?
A rigid extension of a fixed or removable partial denture that transmits functional forces to the teeth and prevents movement toward the mucosa
What is a rest seat?
The portion of a natural tooth or cast restoration prepared to receive an occlusal, incisal, lingual, internal, or semi-precision rest
What are the functions of rests?
- Direct forces down the long axis of teeth
- Prevent cervical movement of the RPD
- Limit lateral movement of the RPD
- Maintain retentive arm in proper vertical relation
- Improve the occlusal plane
What can happen if rests do not prevent cervical movement of the RPD?
the underlying hard and soft tissues may be damaged
What is the guiding principle of rest seat preparation?
Evaluate inter-occlusal/inter-incisal relationships in both static & excursive movements
What are the different types of rests?
Occlusal
Embrasure
Cingulum
Hooded
Incisal
Ball
Where are the occlusal rests located?
- Mesial/distal pits of premolars and molars
- Centered over the marginal ridge whenever possible
What are the different shapes of the occlusal rest seats?
- concave/”spoon” shaped
- “ball and socket”
- triangular
If an occlusal rest seat is a “ball and socket” type what type of sphere is it?
less than half of a sphere
If an occlusal rest seat is triangular in shape, the base of the triangle is…
over the marginal ridge
What should the width be of an occlusal rest seat?
- 1/3 of the buccolingual width
- 1/2 the width between cusp tips
What should the depth be of an occlusal rest seat over the marginal ridge?
1.0-1.5 mm
What should the dpeth be of an occlusal rest seat at the deepest portion?
1.5-2.0 mm
Where is the deepest portion of an occlusal rest seat?
pit area of the tooth
The floor of rest seat should incline towards the axial center, forming an angle less than…
90 degrees
Preparation on the tooth for an occlusal rest seat should be…
wide and shallow
or
deep and narrow
wide and shallow
What is the purpose of an extended occlusal rest?
- Designed to ensure maximum bracing from the tooth.
- The extended rest would ensure that the forces are directed down the long axis of the abutment
Where are embrasure rest seats located?
- two adjacent posterior teeth
(used when no posterior modification space is present)
What is the form of an embrasure rest seat?
- Allow adequate tooth
reduction: approximately 1 mm - Prepare “sluiceway” of around 2 mm
What does an embrasure occlusal rest require for additional marginal ridge preparation?
U-shaped trough to accommodate clasp assembly adjacent marginal ridges
What is the depth and width of the marginal ridge preparation for an embrasure occlusal rest?
Depth: ~1mm
Width: ~2mm
How do you determine occlusal clearance for an embrasure rest seat?
placing two pieces of 18-gauge wire across the preparation
What are the indications for lingual rest seats?
- canines having a gradual lingual slope
- canines using composite resin
- most anterior teeth if placed in cast restorations
Where is a cingulum rest seat located?
Thick well-defined cingulum enamel
* Maxillary - cut into enamel
* Mandibular - composite resin
