Clasp Design & Selection

Introduction to Clasps

  • Importance of clasps in removable prosthodontics

  • Discussion focuses on direct retainers and clasp assemblies

  • Review of previous topics: partial framework, major and minor connectors, rests, proximal plates, meshwork

Direct Retainers

  • Definition: Also known as clasp assembly

  • Components of a direct retainer:

    • Rest: Provides support

    • Minor Connector: Provides stability

    • Clasp Arms: Focus of this video

      • Retentive Clasp Arm (RA): Provides retention

      • Reciprocal Clasp Arm (RBA): Braces against the tooth surface for stability

Clasp Design Types

  • Extra Coronal Retainer: Conventional clasp design

    • Should encircle the tooth at least 180 degrees

  • Intracoronal Retainer: More aesthetic design

    • Utilizes precision attachments with key and keyway patterns

    • Requires careful planning, involves survey crowns

Retentive Clasp Mechanics

  • Originates from minor connector and rest

  • Classified into thirds:

    • Occlusal Third: Offers support

    • Middle Third: Provides stability

    • Gingival Third: Offers retention

  • Contact point of retentive clasp tip:

    • Must engage under the height of contour (survey line)

    • Engages during dislodging forces only

Reciprocal Clasp Mechanics

  • Contacts the tooth above the height of contour

  • Provides stability during retention exerted by the retentive clasp

  • Typically located on the opposite side of retentive clasp

Clasp Categories

  • Supra Bulge Clasps: Originate above the survey line

    • Examples:

      • Circumferential (Akers) clasp

      • Ring clasp

      • Combination clasp

      • Brazier clasp

  • Infra Bulge Clasps: Originate below the survey line

    • Examples:

      • T-bar clasp

      • Modified T-bar clasp (r-bar)

      • I-bar clasp

Clasp Assembly Names

  • RPI: Rest, Proximal Plate, I bar

    • Provides class two lever system design

  • RPA: Rest, Proximal Plate, Akers clasp

  • RPC: Rest, Proximal Plate, Circumferential clasp

Clasp Selection Considerations

  • Important for treatment planning and prosthodontic design

  • Wrought Wire Clasps: More flexible, recommended for compromised teeth

    • Reduces torque on teeth

  • Ideal clasp designs for bounded edentulous spaces: Akers clasps with adjacent rest seats

  • Clasp preference for distal extension: RPI, RPA, and wrought wire clasps

Framework Material

  • Made out of Cobalt Chromium

    • Properties: 2.3% shrinkage, irregularities and porosity

  • Cold Working: Metal manipulated at ambient temperature

    • Major cause of clasp breakage due to repetitive use

Conclusion

  • Overview of clasps in removable prosthodontics

  • Reinforcement of knowledge through revision recommended

  • Transition to fixed prosthodontics in future discussions