Circumferential Clasp

TYPES OF CLASP ASSEMBLIES
The extracoronal retainer comes in three principal forms
A- Circumferential Clasp
It approach the undercut area from occlusal direction, it is called (occlusally approaching clasp), since it is coming to the undercut area supra-gingivally so called supra-bulge clasp and since it is pulling the tooth during action so called pull clasp.

Circumferential clasp assembly consists of:
1. Buccal retentive arm: The terminal portion of retentive arm is flexible and engages measured undercut.
2. Rigid lingual stabilizing (reciprocal) arm.
3. Supporting occlusal rest.
Assembly remains passive until activated by placement or removal of restoration or when subjected to masticatory forces that tend to dislodge the denture base.

DISADVANTAGES
1- More tooth surface is covered than with a bar clasp arm.
2- It may increase the width of the occlusal surface of the tooth.
3- More metal may be displayed than with the bar clasp arm.
4- As with all cast clasps, true adjustment is impossible.

TYPES OF CIRCUMFERENTIAL CLASP

1- The basic form of the circumferential clasp
It is a buccal and lingual arm originating from a common body

This clasp is used improperly when two clasp arms originate from the body and occlusal rest areas and approach bilateral retentive and non-retentive areas on the sides of the tooth away from the point of origin.

2- Ring clasp
It encircles nearly all of a tooth from its point of origin. It is used when a proximal undercut cannot be approached by other means. For example, when a mesiolingual undercut on a lower molar abutment cannot be approached directly because of its proximity to the occlusal rest area and cannot be approached with a bar clasp arm because of lingual inclination of the tooth, the ring clasp encircling the tooth allows the undercut to be approached from the distal aspect of the tooth.
The clasp should never be used as an unsupported ring, because if it is free to open and close as a ring, it cannot provide either reciprocation or stabilization.
It should always be used with a supporting strut on the non-retentive side, with or without an auxiliary occlusal rest on the opposite marginal ridge.
The advantage of an auxiliary rest is that further movement of a mesially inclined tooth is prevented by the presence of a distal rest.
Esthetics need not be considered on such a posteriorly located tooth.

3- Embrasure clasp (Butterfly clasp)
It always should be used with double occlusal rests. This is done to avoid interproximal wedging by the prosthesis, which could cause separation of the abutment teeth and result in food impaction and clasp displacement.
In addition to providing support, occlusal rests also serve to shunt food away from contact areas.
Embrasure clasps should have two retentive clasp arms and two reciprocal clasp arms, either bilaterally or diagonally opposed.

4- Multiple clasp
The multiple clasp is simply two opposing circumferential clasps joined at the terminal end of the two reciprocal arms.
It is used when additional retention and stabilization are needed, usually on tooth-supported partial dentures. It may be used for multiple clasping in instances in which the partial denture replaces an entire half of the dental arch. It may be used rather than an embrasure clasp when the only available retentive areas are adjacent to each other. Its disadvantage is that two embrasure approaches are necessary rather than a single common embrasure for both clasps.

5- Half-and-half clasp
The half-and-half clasp consists of a circumferential retentive arm arising from one direction and a reciprocal arm arising from another.

The second arm must arise from a second minor connector, and this arm is used with or without an auxiliary occlusal rest. Reciprocation arising from a second minor connector can usually be accomplished with a short bar or with an auxiliary occlusal rest, thereby avoiding so much tooth coverage. There is little justification for the use of the half-and-half clasp in bilateral extension base partial dentures.

6- Reverse-action clasp (hairpin)
The reverse-action clasp arm is designed to permit engaging a proximal undercut from an occlusal approach.









? Other methods of accomplishing the same result are with a ring clasp originating on the opposite side of the tooth or with a bar clasp arm originating from a gingival direction. However, when a proximal undercut must be used on a posterior abutment and when tissue undercuts, tilted teeth, or high tissue attachments prevent the use of a bar clasp arm, the reverse-action clasp may be used successfully.
Although the ring clasp may be preferable, lingual undercuts may prevent the placement of a supporting strut without tongue interference. In this limited situation, the hairpin clasp arm serves adequately, despite its several disadvantages.
The clasp covers considerable tooth surface and may trap debris; its occlusal origin may increase the functional load on the tooth, and its flexibility is limited.
Esthetics usually need not be considered when the clasp is used on a posterior abutment, but the hairpin clasp arm does have the additional disadvantage of displaying too much metal for use on an anterior abutment.
Properly designed, the reverse-action clasp should make a hairpin turn to engage an undercut below the point of origin.
The upper part of the arm of this clasp should be considered a minor connector, giving rise to the tapered lower part of the arm. Therefore only the lower part of the arm should be flexible. With the retentive portion beginning beyond the turn, only the lower part of the arm should flex over the height of contour to engage a retentive undercut. The bend that connects the upper and lower parts of the arm should be rounded to prevent stress accumulation and fracture of the arm at the bend.

7- Back-action clasp
The back-action clasp is a modification of the ring clasp. Back-action circumferential clasp is used on premolar abutment anterior to edentulous space. The undercut can usually be approached just as well using a conventional circumferential clasp, with less tooth coverage and less display of metal. With the circumferential clasp, the proximal tooth surface can be used as a guiding plane as it should be, and the occlusal rest can have the rigid support it requires. An occlusal rest always should be attached to some rigid minor connector and should never be supported by a clasp arm alone. If the occlusal rest is part of a flexible assembly, it cannot function adequately as an occlusal rest.