Final answer:
Orthodontic fixed appliances, commonly known as braces, apply force to realign teeth, which are held in the jaw by a gomphosis joint.
Step-by-step explanation:
Orthodontic fixed appliances are commonly known as braces. Braces consist of brackets attached to the teeth and connected by a wire that applies force to correct dental alignment. This force is necessary to realign the teeth because they are anchored into the jaws by a type of joint known as a gomphosis, which is a fibrous joint where the tooth is pegged into the bony socket of either the maxillary bone (upper jaw) or the mandible bone (lower jaw). Gomphoses are held by the periodontal ligament and are functionally immobile since they are classified as synarthrosis joints. Therefore, orthodontic treatment must apply consistent and directed force to move teeth into the desired position.