After enduring two years of braces, patients do not want to experience a relapse. To prevent teeth from returning to their original position, orthodontists instruct their patients to wear retainers. Because those appliances help to keep teeth straight, they must be stable in a patient's mouth. The most common removable retainer is called a Hawley retainer. In order to achieve the necessary stability, Hawley retainers contain clasps. Kinds of clasps are circumferential, Adams, ball, arrow and delta.
Circumferential clasps, which also are known as C-clasps, are the most commonly used clasps on orthodontic retainers. They're formed around molar teeth in a path that parallels the gum line. As their name implies, the clasps follow the circumference on the facial side of the molar tooth, beginning in the acrylic part of the retainer and ending as a free terminal in an undercut of the molar crown. The free end of the wire allows these clasps to be adjusted easily.
Adams clasps do not have a free terminal end of wire, unlike circumferential clasps. Instead, both parts of these clasps are connected to the acrylic part of the retainer. Each Adams clasp contains two small bends in the wire that fit in the undercuts of the molar crown, providing retainer stability. Adams clasps can be purchased pre-bent, or they can be custom-bent during retainer fabrication.
Ball clasps are easily recognisable because they consist of a wire with a small metal ball at its tip. The wire starts in the acrylic part of the retainer and crosses between two teeth to reach the facial part of the teeth, like all other clasps. The ball-end of a ball clasp fits between two teeth on the facial side, and the ball engages in that slight undercut to provide retainer stability.
Arrow clasps are essentially one-half of an Adams clasp. Like ball clasps, they engage the small undercut formed between two adjacent teeth on the facial side. They are used in patients with large undercuts, in which ball clasps would provide too much retention. Excessive retention may make it too difficult for a patient to insert and remove the retainer.
Delta clasps are similar to Adams clasps, but they contain small loops, or helices. While an Adams clasp has two small bends in the wire, a Delta clasp has two small helices that engage the undercuts on the molar crown. Because of the helices, Delta clasps are slightly more bulky than Adams clasps, but both types provide similar amounts of retention.