Describe how a clasp provides retention, support and bracing. Discuss the affect that the Modulus of Elasticity of an alloy has on a clasp design.

Describe how a clasp provides retention, support and bracing. Discuss the affect that the Modulus of Elasticity of an alloy has on a clasp design.

1. A clasp assembly is the part of an RPD that acts as a direct retainer and/or stabilizer for the prosthesis by partially encompassing or contacting an abutment tooth. The clasp is the component of the clasp assembly that engages a portion of the tooth surface and either enters an undercut for retention or remains entirely above the height of contour to act as a reciprocating element.

2. The part of the clasp assembly that enters an undercut for retention is frequently called the retentive clasp arm. Retention of a clasp assembly is provided by the resistance to flexure of the retentive clasp arm as it engages the height of contour of the tooth as the RPD moves occlusally/incisally. Some retention of a clasp assembly may also be provided by frictional contact of rigid portions of the clasp assembly, such as the proximal minor connector and reciprocal component, with surfaces of the tooth which are parallel to the path of placement of the RPD.

3. Support of a clasp assembly is provided by positive contact of the rest of the clasp assembly with the rest preparation of the abutment tooth.

4. The lateral forces in particular are capable of inflicting considerable damage on the periodontal tissues and alveolar bone in the edentulous areas. Thus they have to be carefully controlled. Bracing on teeth may be achieved by means of rigid portions of clasp arms or plates.

5. Modulus of elasticity is the pressure required to effect unit strain. This means that a material having a higher modulus of elasticity will be stiffer. It would require more force to deflect it to the same degree as a material with a lower modulus. This affects the clasp design in the surveying process, because the stiffness of the material will change the depth of undercut it will engage. Also, the MoE of an alloy can determine the thickness and lengths of the clasps, this is because the thicker the clasp they more rigid they are.