Retainers are orthodontic appliances that keep the teeth in place, preventing undesired tooth displacement. Removable retainers have stainless steel wires embedded in plastic; the wire and plastic components restrain the teeth, preventing the teeth from drifting out of place. They also allow for some degree of desirable movement, for the settling of the occlusion that occurs soon after the braces are removed. A good settling of the upper and lower teeth will give you a good bite. Retainers are usually worn at night. They can be removed the next morning for cleaning. As they are easily cleaned, they do not cause any tooth decay.
Functional appliances are specially-designed removable braces for individuals with problems like excessively protruded teeth, overbite problems, or problems with jaw growth. These functional appliances are effective in correcting misalignment by improving biting and jaw position. Functional appliances are worn to help in the development of the jaw. They may also modify the development of the lips, cheeks & tongue. There are many types of functional appliances. Most of them are removable, although some of them are fixed onto the teeth, such as the Herbst appliance, Forsus appliance, MARA appliance.
Removable functional appliances are more hygienic and less likely to break or cause tooth decay. They connect the upper and lower dentition and jaws together by means of plastic and wires. They may be made as two separate pieces for the top & bottom jaws, or they may be fused together as a single piece that fits both the top & bottoms jaws in a certain position. The plastic or wires guide the tongue, lips, cheeks & jaws by stretching, shielding, or re-positioning, producing a more conducive environment for the tissues to grow & develop.