The hard part of the snap ring is placed in the non-undercut area of u200bu200bthe adjacent abutment to act as a splint; while the elastic part extends to the undercut area of u200bu200bthe other adjacent abutment for retention. It is often used for abutments with loose abutments near the gap or with poor crown profiles. Extension snap rings can be cast or bent. It is placed on more than two remaining teeth and is usually made of stainless steel wire. This snap ring has no free arm end, and the middle part of the continuous snap ring arm is used to enter the undercut area of u200bu200bthe abutment to retain the place with greater elasticity. The rest of the snap ring is flush with the observation line, and the snap ring body passes through (occlusal) outside The expansion gap extends to the lingual side and is buried in the base. The clasp is mostly used for the restoration of dentition defects in patients with periodontal disease. It not only repairs the missing teeth, but also can be used to make a periodontal splint with the continuous clasp arm and the lingual base to fix the loose teeth. The clasp is also known as the hard part connecting the clasp arm, the support and the small connecting body. It is surrounded by the non-undercut area of u200bu200bthe abutment. The function of stabilizing and supporting the denture, while supporting the clasp arm, requires the clasp body to have high strength, be not easily deformed, be located in the non-undercut area, and not affect the occlusion.