Clasps

Functional requirements of a clasp:– Retention. Resist removal of R.P.D. occlusally.

– Reciprocation. Resist lateral forces exerted on an abutment tooth as the retentive tip flexes in and out of the undercut.

– Bracing. Resist anteroposterior and lateral shifting of the entire R.P.D.

– Encirclement. Surround more than 180 degrees of an abutment’s circumference so that the tooth does not drift.

Clasp Assembly

The clasp assembly includes rest and minor connectors

The functional requirements of the clasp assembly also includes Support

Support is achieved through the rest

component

Major clasp classifications

Circumferential clasps (Suprabulge or Akers)

Bar clasps (infrabulge or Roach)

Circumferential clasps (Suprabulge or Akers ) Body, retentive arm, retentive tip, reciprocal

arm, and shoulder.

Approaches the undercut from the occlusal portion of the tooth.

Examples: simple circlet (circumferential), back action ,embrasure etc .

Bar clasps (infrabulge or Roach)

Body, approach arm, retentive tip, bracing tip, reciprocal arm, and shoulder.

Approaches the undercut from the gingival portion of the tooth.

Examples: I-bar, T-bar, Modified T

The clasp arm is tapered to increase flexibility

A continuous clasp needs bracing on all teeth that it contacts.

Block-out1. Bulk block out major undercuts

2. Block out undercuts around abutment teeth.

3. Relief wax on saddle areas. 24gauge.– a. Internal finish lines- provide a definite joint

between the metal and resin portion of the appliance.

– b. Tissue stop are placed on the ridge of distal extension by cutting a 2 x 2mm square in the relief wax

Duplication

1 Soak stone cast for 30 minutes in SDS water, 90 degrees F, to eliminate air from the casts and replace it with water so casts will not draw moisture from hydrocolloid and adhere to the cast.

Duplication

Dupli-All duplicating material is an Agar Hydrocolloid.

The pouring temperature is 50 degrees Celsius.

Melt down temperature is 90 degrees Celsius.

Duplication

Duplicating material must cool

Red-stripe investment is a phosphate-bonded investment

The liquid used with Red-stripe investment is water.

Wax dip

Dehydrate the refractory cast to prepare for wax dipping

Place in dehydration oven for 1 hour

Wax dipping ensures a smooth dense cast

Wax-up

Use combination of pre-formed pattern and free flown wax.

Sprue and Invest

A sprue provides a passageway for molten metal during casting

Auxillary sprues are used to ensure complete casting to thicker areas

The ratio for outer investment is 60 cc of 30% Begosol solution to 400 grams of investment

Burnout

Thermal expansion of investment occurs during burnout.

Casting

Induction casting machine uses 220 volts of electricity.

The electric casting machine also uses water

Bego casting machine used positive pressure from above and vacuum from below

Casting

A dark shadow will disappear when metal is ready to cast.

Casting

Acetylene and oxygen can be used to melt Cobalt-chromium metal.

50% new chrome cobalt should be added to an existing button to make a casting