Cast Circumferential Clasp

Definition

“A clasp that encircles a tooth by more than 180 degrees, including opposite angles, and which usually has total contact with the tooth (throughout the extent of the clasp), with at least one terminal being in the infrabulge (gingival convergence) area” - GPT.

They are popularly known as Aker’s clasps. These clasps embrace more than half of the abutment tooth. They may show a continuous or a limited three-point contact with the tooth. This architecture helps the clasp to hold the abutment firmly enough to prevent the rotation of the denture. They approach the undercut from an occlusal direction.

Advantages

• Easiest clasp to make and repair.
• Less food retention
• Best when applied in a tooth supported partial denture.
• Derives excellent support, bracing and retention.

Disadvantages

• It covers a large tooth surface area. It also alters the Buccolingual width of the crown. This affects the normal food flow pattern leading to food accumulation. This causes decalcification of the tooth structure. Damage to soft tissue will occur due to lack of physiological stimulation.
• Difficult to adjust with pliers because of it’s half-round configuration.
• If these clasps are placed high (more occlusally) on the tooth, the width of the food table increases leading to generation of greater occlusal forces.
• All cast circumferential clasps should never be used to engage the mesiobuccal undercut of an abutment adjacent to the distal edentulous space. Hence, they cannot be used for cases with an undercut away from the edentulous space.

Types of Cast Circumferential Clasps

Simple circlet clasp

• Most versatile and widely used.
• Best for tooth supported Partial dentures.
• It approaches the undercut from the edentulous space.
• It engages the undercut, located away from the edentulous space.
• Clasp can be adjusted only in one direction (i.e. buccolingually but not occlusogingivally).
• They cannot be used for distal extension cases as they engage a mesiobuccal undercut.

Reverse circlet or reverse approach clasp

• This clasp is used when the retentive undercut on the abutment tooth is located adjacent to the edentulous space.
• Consider a distal edentulous condition. Usually the clasp will arise from the distal surface of the abutment to reach the mesial undercut. But this clasp is designed in such a way that the clasp arises from the mesial side and ends on the distal undercut.
• Usually Bar clasps are preferred for distal extension cases. These clasps are used when a bar clasp is contraindicated.

Ex: 1.If there is an undercut area in the ridge 2.Presence of a soft tissue undercut caused by buccoversion of the abutment tooth.

• These clasps are used in distal extension denture base to control the stresses acting on the terminal abutment teeth on the edentulous side.

Disadvantages

• If sufficient occlusal clearance is not present, the thickness of the clasp has to be reduced. This will affect the strength of the clasp.
• The occlusal rest away from the edentulous space does not protect the marginal ridge of the abutment tooth adjacent to the

edentulous space. Hence, an additional rest must be placed to provide the necessary protection.

• Poor aesthetics as the clasp runs from the mesial to the distal end of the facial surface.
• Wedging may occur between the abutment and its adjacent tooth if the occlusal rest is not well prepared.

Multiple circlet clasp

• It is a combination of two simple circlet clasps joined at the terminal end of the reciprocal arms.
• It is used for sharing the retention with additional teeth on the same side of the arch when the principal abutment tooth has poor periodontal support.
• It is a mode of splinting weakened teeth.
• It’s disadvantages are similar to that of simple and reverse circlet clasps.

Embrasure clasp or modified crib clasp

Embrasure clasp

• It is a combination of two simple circlet clasps joined at the body.
• It is used on the side of the arch where there is no edentulous space.
• The clasp crosses the marginal ridges of two teeth to form the double occlusal rest. The clasp emerges on the facial surface and splits into two retentive arms. Each retentive arm engages the undercut located on the opposite side of the tooth.
• Interproximal tooth structure should be removed to provide sufficient thickness of the metal. The clasp may break if the metal

is too thin.

Ring clasp

• Consider a distal edentulous condition with a distolingual undercut where a reverse circlet clasp cannot be placed (no buccal undercut). In such cases, the retentive arm is extended all around the tooth from the distobuccal end to terminate in the distolingual undercut across the mesial side of the tooth.
• It is used in cases with lingually tipped molar abutments. Mandibular molars usually tip mesiolingually and the maxillary molars tip mesiobuccally. Hence, the retentive undercut will be on the mesiolingual side for the lower molar and mesiobuccal side for the upper molar.
• As the clasp is long, additional support should be provided by adding an auxiliary bracing arm from the denture base minor

connector to the center of the ring clasp on the buccal surface.

Disadvantages

• Alteration in the food flow pattern.
• It cannot retain its physical qualities.
• Difficult to adjust or repair.
• Increased tooth surface coverage.

Contraindications

• If the buccinator’s attachment lies close to the lower molar.
• If the bracing arm will have to cross a soft tissue undercut.

Fishhook or hairpin clasp or reverse action clasp

• It is a type of simple circlet clasp, which after crossing the facial surface of the tooth loops back to engage the proximal undercut beneath its point of origin. It is used in conditions where the undercut is near the edentulous space.
• Upper arm is rigid and the lower arm is flexible. The upper arm should be positioned above the height of contour in such a way that it does not interfere with occlusion.

Indications

• The undercut is adjacent to edentulous area.
• Presence of a soft tissue undercut.

Disadvantages

• It has poor aesthetics.
• It tends to trap and accumulate food debris.

Onlay clasp

• It is an extension of a metal crown or onlay with buccal and lingual clasp arms.
• It is used in the occlusal surfaces of submerged abutment teeth (that are below the occlusal plane) so that the normal occlusal plane can be restored with an onlay.
• If the onlay clasp is made of chrome alloy, the opposing tooth should be protected with a gold crown. Because the chrome alloy can produce massive attrition of enamel.
• As this clasp covers large amount of tooth structure, it may lead to breakdown of enamel surfaces. Hence, it should be used only in a caries resistant mouth.

Half and half clasp

• It has a retentive arm arising from one direction and a reciprocal arm arising from another.
• Two minor connectors are needed for this design. The first minor connector attaches the occlusal rest and the retentive arm to the major connector. The second minor connector connects the reciprocal arm, which is similar to the bar clasp with or without an auxiliary rest.
• This design produces large tooth coverage, which can be reduced by converting the reciprocal arm into a short bar with an auxiliary occlusal rest.
• This design is intended to provide dual retention.

Back-action clasp

• It is a modification of the ring clasp.
• Here the minor connector is connected to the end of the clasp arm and the occlusal rest is left unsupported.

Disadvantages

• Lack of support to the occlusal rest reduces its function.
• It has both biological and mechanical unsound principles.

Grasso’s clasp or VRHR clasp

Developed by Grasso, this clasp consists of a vertical reciprocal arm, an occlusal rest and a horizontal retentive arm each arising separately from the major connector. It is more of a proposed concept.

Advantages

• Minimizes tooth contact without compromise in efficacy.
• Does not require the preparation of guide planes.
• Suitable for posterior teeth with high survey lines.
• The placement of the retentive arm is more aesthetic.
• The balance between the retentive and reciprocal components prevents the whiplash effect of the retentive arm.

Disadvantages

• Difficult to maintain as the block out zone between the base of the reciprocal arm and the tooth tends to collect food debris.

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