What are the components of a clasp?

　　ClaspIt is the main retainer of removable dentures, directly clipped onto the main abutment teeth, made of metal. It plays a role in retention, stability, and support. Taking a typical cast three-arm clasp (conventional clasp) as an example, it consists of a clasp arm, clasp body, support, and connector.

　　I. The composition of the clasp is as follows:

　　1. Clasp arm

　　The clasp arm is the free part of the clasp and is elastic. The end of the clasp arm is located in the undercut area, which is the main part of the clasp retention effect. When the denture is inserted, the clasp retains the elasticity of the arm end and enters the undercut area through the contour protrusion of the abutment crown. When misalignment forces act, it will prevent the denture from being misaligned in the occlusal direction. In the process of the clasp retention arm entering and leaving the undercut area through the high point of the abutment contour, the horizontal component force generated by the clasp retention arm on the abutment should be offset by the correspondingly designed clasp counter-arm or guide plate, small connector, etc., to avoid damage to the abutment caused by lateral forces. The starting part of the clasp arm should be rigid and placed in a non-undercut area to stabilize and prevent lateral displacement of the denture. The shape of the clasp arm depends on the material and manufacturing method used. There are three types of clasp arms: round, semi-circular, and flat.

　　2. Clasp body

　　Also known as the clasp shoulder, it is the rigid part that connects the clasp arm, support, and small connector. It encircles the non-undercut area of the abutment and passes through the buccal-lingual axial angle from the adjacent surface to prevent gingival and lateral movement of the denture, which plays a role in the stability and support of the denture. At the same time, it supports the clasp arm. Therefore, it is required that the clasp body has high strength, is not easily deformed, is located in the non-undercut area, and does not affect occlusion.

　　3. Small connector

　　It is the part where the clasp is embedded in the base or connected to the main connector, mainly used to connect the clasp and other parts of the denture. The connector must not enter the undercut area of the abutment or soft tissue, so as not to affect the positioning.

　　4. Support

　　It is usually cast integrally with the clasp. The so-called three-arm clasp is a general term for the arms.

　　II. Classification according to the number of clasp arms:

　　It can be divided into single-arm clasp, double-arm clasp, and three-arm clasp.

　　1. Single-arm clasp: It has only one clasp arm, usually bent from wire. The elastic part at its end enters the undercut area of the abutment tooth for retention. When using a single-arm clasp, the lingual (palatal) side must be supported by the base to prevent displacement of the abutment tooth under force. The clasp has no support function. Another commonly used single-arm clasp in clinical practice is the interdental clasp, also known as the interdental clasp, the (occlusal) and buccal-distal space between the abutment tooth and the adjacent teeth (the gap clasp must first be prepared in the (occlusal) distal space), the lingual side is relatively high. In addition to the retention function, the interdental clasp also has the support function through the (occlusal) distal space.

　　2. Double-arm clasp: It has two clasp arms, one buccal and one lingual. The buccal side is the retention arm, and the lingual side is the counter-arm. It is mainly used for abutment teeth with poor periodontal health, slight loosening, which cannot be placed with occlusal support, or when the occlusion is too tight to prepare abutment teeth with support undercut. The double-arm clasp is only used for retention.

　　3. Three-arm clasp: It consists of buccal and lingual clasp arms and occlusal support, with good support, retention, and stability. It is used for posterior teeth with stable teeth, healthy periodontal tissues, and sharp clasps retained in the crown shape. It is a commonly used clasp clinically. It can be cast or bent, and the lingual arm can also be replaced by a base.