1. Rest
   1. It's a rigid extension of RPD that prevents movement towards mucosa & transmits functional forces to teeth
   2. Types
      1. Occlusal rests
      2. Lingual/Cingulum rests
      3. Incisal rests
   3. Can be placed upon
      1. Sound enamel
      2. Silver amalgam
      3. Cast restorations
2. Rest seat
   1. The prepared recess in a tooth/ restoration created to receive occlusal, incisal, cingulum/lingual rest
3. Functions of Rest & Rest seat
   1. 1. Support
      1. Primary function is to provide support to the RPD
   2. 2. Force transfer
      1. Aids in transferring force along long axis of tooth
   3. 3. Indirect retention
      1. Rests are positioned anterior & posterior to axis of rotation to prevent distal extention base from lifting
   4. 4.Positional maintenance
      1. Rigidity of rest helps in maintaining clasp assembly in proper position
   5. 5. Stability
      1. Thickness & position of rest helps in stability denture with other components of RPD. In distal extention cases, rest seat should be shallow & saucer shaped
   6. 6. Establishing occlusal plane
      1. Helps in establishing occlusion plane in cases of tipped molars.
   7. 7. Prevent food impaction
      1. Rest placed closed to edentulous space prevents food impaction in abutment minor connector interface
   8. 8. Prevent tooth migration
      1. Rest placed on proximal surface of teeth adjacent to edentulous space prevents tooth migration & thus maintain small edentulous spaces
   9. 9. Reciprocation
      1. Helps in reciprocating stresses generated by retentive arm of clasp assembly on abutment teeth
4. Occlusal rest
   1. Outline form is a rounded triangular shape
      1. Apex at centre of occlusal surface & base at the marginal ridge
   2. Floor of the rest seat should be apical to marginal ridge & occlusal surface should be concave or spoon shaped
      1. Spoon shaped - so that it directs the forces along long axis of tooth
   3. Angle formed by occlusal rest & vertical minor connector should be less than 90°
   4. Bur used - Diamond No. 6 or 8 round burs
   5. Note : In completely tooth borne RPD, occlusal rests transmit - 100% of occlusal forces to the teeth
5. Lingual/Cingulum rest
   1. Indications
      1. If anterior tooth has gradual lingual slope rather than perpendicular
      2. Used mostly on maxillary canines than on incisors/mandibular canines
      3. On incisors it's indicated only when missing canines or when canines are periodontally compromised
   2. Lingual rest is preferred to an incisal rest because
      1. More esthetic
      2. Exerts less leverage on tooth
      3. It's placed near the centre of rotation of supporting tooth so that it doesn't tip the tooth
   3. It's slightly rounded V shaped with apex of V directed incisally
      1. Bur used - 1/4th inch diamond disk
6. Incisal rests
   1. Least desirable position rest placement. Used on sound tooth & never on cast restorations
   2. Mainly used as indirect retainers
   3. Frequently used on mandibular canines, rarely on maxillary canines. In incisors, they're generally not used, but if required multiple rests are placed
   4. They're placed on mesioincisal/ distoincisal angle of tooth depending whether tooth is to be clasped. If tooth is not clasped, rest is placed on distoincisal angle for aesthetics
   5. Cast circumferential clasp - Distoincisal angle Bar clasp - Mesial incisal angle
   6. Dimensions
7. OTHER KEY POINTS
   1. Intracoronal or internal rest don't increase/provide retention
   2. Internal occlusal rest provides Vertical support & horizontal stability
   3. Reasons for failure of rest seat in RPD
      1. Inadequate depth of rest seat preparation
      2. Improper rest seat preparation