Functional appliances use the muscle action from speaking, eating and swallowing to create forces that move the teeth and align the jaws. Functional appliances can be removable or fitted onto the teeth.
Fixed appliances are fitted onto the teeth and are commonly called braces. Over a period of time, the wires are tightened and adjusted, gradually applying gentle force to move the teeth.
Retainers are removable appliances which hold the teeth in place after braces are taken off.