rest & rest seats in rpd

Rests & rest seats : 

Rests & rest seats P V Badwaik

Rests & rest seats : 

Rests & rest seats Rests - Serve primarily to transfer forces down the long axis of abutment Rest seat – prepared surface of a tooth / fixed restoration into which rest fits Rest & tooth relation – forces transmitted are directed apically down the long axis of tooth, so stress can be absorbed by PDL & no damage to supporting bone

In Tooth-Tissue supported CPD : 

In Tooth-Tissue supported CPD Only a portion of stress is transferred to the teeth & edentulous ridge must absorb the remainder Rest – must also serve as Vertical stop, Preventing Injury, & Overdisplacement of soft tissues Rest – must maintain Clasp in its proper position Primary rest – component part of Direct retainer Secondary/Auxiliary rests – used for indirect retainer

Primary Rest : 

Primary Rest Prevent vertical movement towards the tissue Help transmit lateral/horizontal forces applied to PD – may be increased by deepening the rest seat For Distal Extension PD – shallow & saucer shaped (rest can move slightly) Food impaction –so rest on proximal-occ/incisal surf Migration/Drifting of teeth – too small space, Metal Pontic

Slide 5: 

Minor connector acts as reciprocal clasp arm Large Occlusal Onlay rest – on tipped molar – produces acceptable occlusal plane 3 forms – Occlusal rest , Lingual/Cingulum rest, Incisal rest

Occlusal rest : 

Occlusal rest

Occlusal rest : 

Occlusal rest Rest should be always placed on Rest Seat

Occlusal rest : 

Occlusal rest

Occlusal rests in Amalgam/Gold restorations : 

Occlusal rests in Amalgam/Gold restorations Chances of amalgam fracture Full coverage crowns are good

Lingual/Cingulum rest : 

Lingual/Cingulum rest Maxillary Canines – minimum tooth prep Multiple Incisor teeth with lingual rest – to distribute stresses over number of teeth More leverage forces

Cingulum rest : 

Cingulum rest

Lingual rest VS Incisal Rest : 

Lingual rest VS Incisal Rest Lingual rest is nearer the centre of rotation – prevent tipping Longer minor conn. required for incisal rest magnifies the forces being transferred Lingual rest is more acceptable esthetically

Form of Lingual rest : 

Form of Lingual rest Half – moon, V-shaped, labiogingival angle < 900

Incisal rest : 

Incisal rest Mandibular canines Stabilization of incisor teeth (incorporated in Lingual plate) Placed on Disto-incisal angle Small V-shaped notch 1.5 – 2 mm from proximo-incisal angle, Deepest portion – toward center of tooth mesiodistally Notch must be rounded & extended slightly on facial surface – provide positive seat Enamel on lingual surf is prepared to accommodate minor conn – avoid annoying tongue Maintain rigidity

Form of Incisal rests : 

Form of Incisal rests