72 - Metal cast clasps – parts, types.

sections

• types of metal cast clasps

• clasps designed to accommodate movement

• examples of metal cast clasp that accommodate movement types of metal cast clasps

• clasps designed without movement accommodation

• clasp modification

• types of metal cast clasps

• Casts Clasps:

  • Circumferential clasps: (suprabulge)

  • Bar-type clasps: (infrabulge)

• Wire bent clasps:

  • Single shoulder clasp

  • Double shoulder clasp

  • Triple shoulder clasp

  • Jackson's clasp

• Combination clasps: consists of a tapered, round wrought-wire retentive clasp arm and a cast reciprocal arm.

• clasps designed to accommodate movement

• RPI (rest, proximal plate, I-bar)

• RPA (rest, proximal plate, Aker's clasp)

• Bar clasps (T, modified T, I and Y)

• These clasps accomplish movement accommodation by changing fulcrum location. For this we use RPI (Rest, Proximal Plate, I-bar) claps and RPA (Rest, Proximal Plate, Aker’s).

• T-clasps and Y-clasps are also used (only difference is the angle of the arm).

• If the bar clasp arm is made to be flexible for retentive purposes, any portion of the clasp above the height of contour will provide only limited stabilization, because it is also part of the flexible arm. Therefore, in many instances, this suprabulge portion of a T or Y clasp arm may be removed.

• examples of metal cast clasp

1. One-half T-type bar clasp: distobuccal undercut; the portion of the clasp arm on and above the height of contour might afford some stabilization against horizontal rotation of the denture base.

2. I-bar: undercuts in middle (anteroposteriorly) of the buccal side: this retainer contacts tooth only at its tip; a mesial rest is used.

3. Interproximal ring clasp: distobuccal undercut; used when we have inferior tissue undercut on the buccal surface of the abutment.

4. Round tapered wrought-wire circumferential retainer arm: mesiobuccal undercut; uses a wrought wire instead of a cast arm, as wrought wire can flex more than cast arm, to avoid excessive stress on tooth.

5. Hairpin clasp: undercut lies cervical to the origin of the retainer arm.

6. Double occlusal rests: the rests connect to lingual Barry a minor connector; eliminates the need for a lingual clasp arm; places the fulcrum anteriorly to make better use of the residual ridge for support, and provides stabilization against horizontal rotation of the denture base.

• clasps designed without movement accommodation

1. Circumferential clasp: buccal and lingual arm originating from the common body, this clasp must have 1 retentive arm and 1 reciprocal arm.

2. Ring clasp: used when proximal undercut cant be reached, it encircles the entire tooth.

3. Embrasure clasp: has 2 retentive clasp arms and 2 reciprocal arms, they are bilaterally apposed, also must have a double occlusal rest (this is important to avoid interproximal wedging of the prosthesis which can cause separation of the abutment teeth.

• clasp modification

• Back action clasp: modification of ring clasp, its use is difficult to justify.

• Multiple clasp: 2 opposing clasps joined at end of reciprocal arm, used when additional retention is needed.

• Half and half clasp: retentive arm arises from 1 side and reciprocal arm from other side → provides dual retention.

• Reverse action clasp/hairpin clasp: allows proximal undercut to be engaged occlusally.