Design form of cast and bent snap rings: Ring snap ring (also known as ring snap ring): mostly used for isolated last molars and inclined to the mesio-buccal (upper jaw) or mesiolingual (lower jaw) side . The snap ring surrounds almost the entire axial surface of the crown, and the snap ring arm has an elastic tip that ends at the mesio-buccal side of maxillary molars or the mesial-lingual undercut area of u200bu200bmandibular molars. The cast ring-shaped snap ring can be designed with two (occlusal) rests at the mesial and distal (occlusal) margins, and its non-retaining side snap ring arms should not be undercut, and should be supported by auxiliary snap arms. The bent ring-shaped clasp only has mesial (occlusal) support, and the non-retaining side clasp arm should extend the base to the distal side to wrap around the base to reinforce and counteract the arm, so as to avoid too long deformation of the clasp arm . Pull-back clasp: commonly used for missing free ends of posterior teeth, abutments are premolars or canines, crowns are short or tapered, and its characteristics are: the tip of the clasp arm is located in the undercut area of u200bu200bthe labial (buccal) side of the abutment, It bypasses the distal surface of the abutment and connects with the (occlusal) rest, then turns to the non-undercut area on the lingual side to form an antagonistic arm, and connects with the palatal (lingual) rod on the mesial and lingual side of the abutment through a small connector. If the tip of the snap ring arm is located in the lingual undercut area of u200bu200bthe abutment (severe inclination of the mandibular abutment to the lingual side), the snap ring arm is connected to the distal (occlusal) rest and turned to the buccal side, passing through a small connector mesially Connected with the base metal bracket, it is called the anti-return force snap ring. Both are cast snap rings. Since 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 teeth and base, and then migrates back to the abutment. This relieves the load on the abutment and has a stress interrupting effect. Joint clasp: It is formed by connecting two clasp through a common clasp body, and the clasp body is connected to the abduction gap of two adjacent abutments (occlusal) and the support of the extending (occlusal) surface. It is suitable for missing teeth on one side of the dental arch, short and stable crowns on the other side of the abutment, or there is a gap between two adjacent teeth. The combined retaining ring supports good retention and stability, and can prevent food impaction. Joint snap rings can only be made by casting. Half Snap Rings: Consists of two separate, opposing ring-shaped clasp arms and a mesiodistal (occlusal) rest, buccolingual, and used on isolated premolars or molars with anterior and posterior gaps. The support and retention of the half snap ring is strong, and its production method can be cast or bent. Canine snap ring: a cast snap ring commonly used on canines. The snap ring is supported from the mesial incisal support along the lingual mesial marginal ridge of the canine down to the lingual carina, and then up through the lingual distal marginal ridge. To the distal incision angle of the canine, it goes beyond the incisal abduction gap and continues to descend to the labial surface to form a snap ring arm, the tip of which ends at the mesial undercut area of u200bu200bthe labial surface. Has good support and retention. Extended Snap Ring: Also known as the long arm snap ring, the snap ring arms are in contact with both abutments at the same time. 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 u200bu200banother adjacent abutment for retention. It is often used for abutments with loose abutments near the gap or with poor crown contours. Extension snap rings can be cast or bent. Continuous snap ring: placed on more than two remaining teeth, usually made of stainless steel wire. This clasp has no free arm end. The middle part of the clasp arm is continuous, and the place with greater elasticity is inserted into the undercut area of u200bu200bthe abutment for retention. The rest of the clasp is flush with the observation line, and the clasp body passes through the (occlusal) outside. The expansion gap extends to the lingual side and is buried in the base. It is mostly used for the restoration of dentition defects in patients with periodontal disease. It not only repairs missing teeth, but also can be used to make a periodontal splint with continuous snap ring arms and lingual base to fix loose teeth. Rod-shaped snap ring: Made by casting method, there are various forms of variants, such as U-shaped, T-shaped, I-shaped, L-shaped, etc. UUUU-shaped snap ring: It is in point contact with the undercut area of u200bu200bthe buccal surface of the abutment. It is suitable for the abutment with a long crown. The observation line is biased towards the eye, and there is an appropriate undercut at the corner of the mesial or distal line. TTTT-shaped clasp: It is the most commonly used form of rod clasp, with good elasticity, and is often used for a removable partial denture with a missing distal extension, but this type of clasp tends to accumulate food and expose metal. IIII-shaped clasp: It is in point contact with the undercut area of u200bu200bthe buccal surface of the abutment, with good elasticity, less exposed metal, more beautiful, and does not impact food, but there must be an opposing arm on the lingual side. LLLL-shaped snap ring: It is in point contact with the undercut area of u200bu200bthe buccal surface of the abutment, with good elasticity and easy cleaning. There are many shapes and types of rod-shaped snap rings, and they are widely used. Its main advantages are good elasticity, small contact surface with the abutment, strong retention, little damage to the abutment, less exposed metal, beautiful appearance, and the abutment can be maintained. Physiological exercise. Its main disadvantage is that the stabilizing effect is not as good as that of the annular snap ring, it is easy to accumulate food, and it is not easy to repair after damage.