Which component is NOT typically considered an active component of removable appliances?

Removable orthodontic appliances are designed to be adjusted and can exert forces to effect tooth movement or guidance, making specific components essential to their active function. Active components are those that intentionally provide force or change the position of teeth when the appliance is used.

Retainers, in contrast, serve a fundamentally different purpose. Their primary role is to maintain the position of teeth after active orthodontic treatment has concluded. Retainers do not actively move teeth but instead help to stabilize them in their new positions. This passive role distinguishes them from components like expansion screws, coil springs, and finger springs that are intentionally designed to apply forces for tooth movement.

Expansion screws create controlled increases in arch width by exerting forces on the teeth, while coil springs apply continuous pressure to space teeth apart or move them into desired positions. Finger springs are also used to apply force for minor movements, like moving a single tooth.

Therefore, since retainers do not actively influence the position of teeth but rather aim to retain the results of previous orthodontic treatment, they are not viewed as an active component of removable appliances. This distinction is vital for understanding the functions of various components in orthodontic practice.