overview of occlusal rests and rest seats

brief description ofocclusal rest and rest seats in cast partial denture

1. RESTS AND REST SEATS Dr.Ajay

2. Definition: REST: A component of a partial denture on a tooth surface that provides vertical support is called a rest REST SEAT : Prepared surface of an abutment to receive the rest is called rest seat

3. Primary use -vertical support 0ther uses -Maintain components in planned positions - Prevent settling of the denture - Prevents impingement -Distributes occlusal load to abutment

4. TYPES Occlusal cingulum incisal rest rest rest

5. OCCLUSAL REST AND REST SEAT: Outline form-rounded triangular shape with apex towards center of occlusal surface Base of triangular shape should be atleast 2.5mm for both molars and premolars The reduction of marginal ridge of approximately 1.5mm is necessary

6. Floor of rest seat-apical to marginal ridge and occlusal surface and concave or spoon shaped The angle formed by the occlusal rest and the vertical minor connector from which it originates should be less than 90 degree

7. EXTENDED OCCLUSAL RESTS: Used in posterior most mesially tipped molars In Kennedy’s class II,modification 1 and kennedy class III Rest should extend morethan one half of mesio distal diameter of tooth and one-third the buccolingual width

8. In severely tilted abutments-the extended occlusal rest may take form of an onlay to restore occlusal plane

9. INTERPROXIMAL OCCLUAL REST SEATS: The design of direct retainer may require this rest Prepared as individual occlusal rest seats with the exception that the preparation must be extended farther lingually Used to prevent interproximal wedging by the framework

10. In addition the joined rests are designed to shunt food away from contact points Analysis of mounted casts is mandatory in this type of rest

11. INTERNAL OCCLUSAL RESTS: A partial denture that is totally tooth supported by means of cast retainers may use this for both occlusal support and horizontal stabilization Occlusal support- floor of rest seat Horizontal stabilization – from near vertical walls of rest seat

12. Main advantage-eliminates visible clasp arm buccally and permits the location of the rest seat in a more favourable position in relation to tipping axis of the abutment Only indication-tooth supported dentures

13. Lingual rests on canines and incisor teeth: A canine is much preferred over an incisor for this purpose, if canine is absent multiple incisor rests are used PREPARATION: Slightly rounded v is prepared at the junction of gingival and middle third of tooth

14. Apex of v is directed incisally Prepared by using an inverted cone shaped diamond stone and progressing to smaller,tapered stones with round ends Floor of rest seat:towards cingulum

15. INCISAL RESTS AND REST SEATS: Placed on incisal angles of anterior teeth It is least desirable and can be used selectively when abutment is sound and cast restoration is othertwise not indicated Used predominantly as auxillary rests or as indirect retainers

16. Preparation: Prepared in the form of a rounded notch at the incisal angle with deepest portion apical to incisal edge Should be approximately 2.5mm wide and 1.5 mm deep

17. Reference: McCracken’s removable partial denture Stewart’s removable partial prosthodontics