Snap rings can be divided into two categories according to the production method
Classification of clasp There are many types of clasp, and the classification methods are different. In addition to the classification according to the relationship between the clasp and the observation line, it is generally classified according to the production method and the number of clasp arms. Classification according to the production method: ①Casting snap ring: It is made by wax type, embedded, and made of high-melting alloy through casting process. Casting snap rings include annular snap rings and rod snap rings. Circular clasp: It surrounds 3 faces and 4 axis angles of the abutment tooth, that is, it wraps more than 3/4 of the crown of the abutment tooth. This kind of snap ring was first applied by Aker (1936), so it is also called Aker snap ring. The annular snap ring is suitable for the abutment teeth with healthy periodontal tissue and good crown shape, and has good supporting, retaining and stabilizing effects. Rod snap ring: Rod snap ring was first proposed by Roach (1934), so it is also known as Roach snap ring. This snap ring has relatively independent buccal and lingual arms. The snap ring arm is protruded from the metal bracket of the base, the retention mesh in the base or the size connector, and is convex from the gum to the abutment. Click on the undercut area. Its retention is a push-type retention from bottom to top, so it is also called a push-type snap ring. It is suitable for the abutment teeth with free and missing posterior teeth. Its retention effect is good, but the stability effect is poor. ②Bending clasp: Bending clasp is made of round stainless steel wire. Generally, the molar clasp uses a steel wire with a diameter of 0.9 to 1.0 mm (20 to 19), and the premolar and anterior clasp uses a diameter of 0.8 to 0.9 mm (20 to 20). The support is made of flattened and bent stainless steel wire with a diameter of 1.2mm (No. 18). It is better to use a cast support. Because this kind of clasp is in linear contact with the surface of the abutment, the contact area is small, the contact area is smooth, easy to clean, the caries-causing rate of the abutment is low, and the production equipment is simple, easy to operate, easy to adjust, economical and durable, so it is still widely used in clinical practice. use.