What are the classifications of clasps?

　　ClaspThere are many types, and different classification methods. In addition to classification based on the relationship between the clasp and the observation line, they are usually classified according to the manufacturing method and the number of clasp arms.

　　Design forms of cast and bent clasps:

　　1. Ring clasp: Usually used for a single molar, and inclined to the mesiobuccal (maxilla) or mesiolingual (mandible) side. The clasp almost surrounds the entire axial surface of the crown, and the elastic end of the clasp arm terminates at the mesiobuccal undercut of the maxillary molar or the mesiolingual undercut of the mandibular molar. Two (occlusal) rests can be designed on the mesial and distal (occlusal) margins of the cast ring clasp. The clasp arm on the non-retained side should not enter the undercut and should be supported by an auxiliary clasp arm. When bending the ring clasp, there is only mesial (occlusal) support. The clasp arm on the non-retained side should extend its base to the distal side for wrapping to strengthen and resist the arm, thus avoiding excessive deformation of the clasp arm.

　　2. Reciprocating clasp: Usually used when there is no free end in the posterior teeth. The abutment tooth is a premolar or canine, and the crown is short or conical. Its characteristics are: the tip of the clasp arm is located in the undercut area on the labial (buccal) side of the abutment tooth, bypasses the distal surface of the abutment tooth to connect with the (occlusal) rest, then turns to the lingual non-undercut area to form the counter-arm, and it is connected to the palatal (lingual) bar through a small connector on the mesiolingual side of the abutment tooth. If the tip of the clasp arm is located in the lingual occlusal margin area of the abutment tooth (the mandibular abutment tooth is severely inclined lingually), the clasp arm connects with the distal (occlusal) rest and turns to the buccal side, and connects to the metal rest of the abutment tooth through a small connector in the mesial part, it is called a reciprocating clasp. Both of these are cast clasps. Because the distal (occlusal) rest is not directly connected to the base, the lifting force is first transmitted to the mucosa and alveolar ridge through the artificial tooth and the base, and then transmitted back to the abutment tooth, which reduces the load on the abutment tooth and has a stress interruption effect.

　　3. Combination clasp: Consists of two clasps connected by a common clasp body. The position of the clasp body is connected with the legs of the two abutment teeth (occlusal) and the rests extending to the occlusal surface. It is suitable for missing teeth on one side of the dental arch, short and stable crowns of abutment teeth on the other side, or gaps between adjacent teeth. The combination clasp has good retention and stability, and can prevent food impaction. Combination clasps can only be made by casting.

　　4. Half clasp: It consists of two separate, opposing buccal-lingual and mesial-distal (occlusal) supported national clasp arms, used for isolated premolars or molars with gaps in front and behind. It has a strong retention effect on the half clasp bracket, and its manufacturing method can be cast or bent.

　　5. Canine clasp: A cast clasp often used for canines. The clasp hook is supported by the mesial incisal tip along the mesial marginal ridge of the lingual surface of the canine down to the lingual prominence, then upwards through the distal marginal ridge of the lingual surface to the distal incisal angle of the canine, and continues to descend through the interproximal space to the labial surface to form the clasp arm, the tip of which terminates in the middle undercut area of the labial surface. It has good support and retention.

　　6. Extended clasp: Also known as a long-arm clasp, the clasp arm contacts two abutment teeth at the same time. The rigid part of the clasp is placed in the non-undercut area of the abutment tooth, close to the gap, acting as a splint; the elastic part extends to the undercut area of another abutment tooth adjacent to it for retention. It is usually used for abutment teeth with loose or poorly shaped crowns near the gap. Extended clasps can be cast or bent.