1. Definition
   1. That component of partial removable dental prosthesis used to retain & prevent dislodgement, consisting of clasp assembly or precision attachment
2. Classification
   1. Intracoronal
      1. Attachments
   2. Extracoronal
      1. Attachments
      2. Clasps
         1. Circumferential
            1. Cast Circumferential
            2. Combination
         2. Bar
3. Clasp assembly
   1. Components
      1. Rest, body, shoulder, retentive arm, retentive tip, reciprocal arm, minor connector
      2. Rest
         1. For support
      3. Minor connector
         1. For Stabilization
      4. Clasp Arms (Retentive & Reciprocal)
         1. For Stabilization & retention
   2. Requirements
      1. 1. Retention
         1. Most important
         2. Should touch the tooth in undercut area
      2. 2. Support
         1. Provided by occlusal, lingual or incisal rests
      3. 3. Reciprocation
         1. Retentive arm passing over height of contour Reciprocal arms passing along reciprocal guiding plane
      4. 4. Encirclement
         1. Clasp assembly should encircle more than 180° of abutment tooth either by continuous or broken contact
      5. 5. Passivity
         1. Retentive function of clasp should be activated only when dislodging forces are applied. All the other times, clasp should be passive
   3. Factors affecting retention
      1. 1. Dimension of retentive undercut
         1. Buccolingual depth
         2. Height of contour
         3. Mesiodistal length
      2. 2. Flexibility of clasp
         1. Length of clasp
            1. ▪︎Greater the length - greater the flexibility
         2. Diameter of clasp
            1. ▪︎Flexibility is inversely proportional to diameter
         3. Cross-sectional form
            1. ▪︎Round cross section has more flexibility than half round. ▪︎Hence, Wrought wire (round) clasp is more flexible than cast clasp
         4. Material
            1. ▪︎Chrome alloys have high rigidity, strength hence less flexible ▪︎Wrought wire clasp has greater flexibility, resilience & yield strength
      3. 3. Type of clasp
         1. Gingivally approaching clasp (push type) retention
            1. ▪︎Better retention than pull type
         2. Occlusally approaching clasp (pull type) retention
4. Circumferential clasp/ Aker's clasp
   1. 9 Types
      1. Circlet clasp
         1. ▪︎Indication : Tooth supported class III RPD ▪︎Undercut - Approaches tooth undercut from edentulous area & engages undercut remote from edentulous space
      2. Reverse circlet
         1. ▪︎Indication : When undercut lies on distobuccal surface of tooth adjacent to edentulous area ▪︎Undercut - engages distal undercut
      3. Multiple circlet
         1. Indication : When principal abutment tooth has lost its periodontal support
      4. Embrassure clasp
         1. ▪︎Indication : on side of arch where there is no edentulous space like unmodified Kennedy's Class II & Class III ▪︎Undercut - it crosses both marginal ridges & engages undercut on opposing line angles
      5. Ring clasp
         1. Indications : Mainly on tipped molars Isolated mesially inclined molars
         2. Modification of Ring clasp - Back action clasp
         3. ▪︎In maxillary molar - retentive undercut located on mesiobuccal line angle ▪︎In mandibular molar - undercut on mesiolingual line angle
      6. Reverse action/Hairpin clasp
         1. Indication : used in conditions where undercut is near edentulous space Used only when bar type retentive arm is contraindicated
      7. Onlay clasp
         1. Indication : When occlusal surface of abutment is below occlusal plane
      8. Back action clasp
         1. Modification of Ring clasp Biologically & mechanically unsound
      9. Half & half clasp
5. Combination clasp
   1. Consists of Wrought wire retentive arm & Cast reciprocal arm
      1. ▪︎It has the highest flexibility ▪︎Originates above the height of contour
   2. Advantages
      1. Increased flexibility & adjustability
      2. Increased esthetics
      3. Easy to adjust, as it can flex in all 3 planes
      4. Less tooth contact due to round nature of clasp arm
   3. Disadvantages
      1. Extra lab procedures
      2. Easily distorted by careless handling
      3. More tooth coverage than Bar clasp
6. Prothero's cone theory
   1. Is the basis of clasp retention
      1. He described the shape of crowns of Premolar & Molar teeth can be considered as 2 cones sharing a common base. The line formed at the junction of these cones represents the greatest diameter of the tooth
7. Bar clasp / Roach clasp/ Gingivally approaching clasp
   1. Push - type retention
      1. More effective than pull type
      2. Retentive terminal is connected to denture base minor connector by "approach arm"
   2. Indications
      1. Small undercut existing in cervical third of abutment
      2. Distal extension abutment to engage a distobuccal undercut
      3. When esthetics demand less display of metal
   3. Contraindications
      1. Large tissue undercut
      2. Deep cervical undercut in abutment
      3. Severe buccal or lingual tilt of abutment
      4. Shallow vestibule
8. RPA Concept
   1. Given by Kroll in 1976
   2. RPA refers to Rest, Proximal plate & Aker's clasp
      1. Indication :- When RPI system cannot be used in cases of tipped abutments & soft tissue undercuts
      2. Use of distal rest & Wrought wire circumferential(Aker's) clasp is indicated
9. RPI Concept
   1. Given by Kroll & Kratchovil
   2. RPI refers to Rest, Proximal plate, I-bar
      1. Mesio-occlusal rest, distal guiding plane prepared to receive proximal plate & I bar located at gingival third of buccal/labial surface of abutment
      2. Distal extension abutment to engage a distobuccal undercut
   3. I-bar clasp (RPI)
      1. ▪︎Greater retention ▪︎ More esthetic ▪︎Covers less tooth structure ▪︎Not indicated when deep cervical tooth undercut ▪︎Not indicated when severe tissue undercut ▪︎Not indicated when there is excessive buccal/lingual tilt of tooth ▪︎Greater tendency of food lodgement