slot in the brackets which allows for controlled movement in all three dimensions. Apart from wires, forces can be applied using elastic bands, and springs may be used to push teeth apart or to close a gap. Several teeth may be tied together with ligatures and different kinds of hooks can be placed to allow for connecting an elastic band. Clear aligners are an alternative to braces, but insufficient evidence exists to determine their effectiveness. Treatment Duration The time required for braces varies from person to person as it depends on the severity of the problem, the amount of room available, the distance the teeth must travel, the health of the teeth, gums, and supporting bone, and how closely the patient follows instructions. On average, however, once the braces are put on, they usually remain in place for one to three years. After braces are removed, most patients will need to wear a retainer all the time for the first six months, then only during sleep for many years. Headgear Orthodontic headgear—sometimes referred to as an "extra-oral appliance"—is a treatment approach that requires the patient to have a device strapped onto his or her head to help correct malocclusion—typically used when the teeth do not align properly. Headgear is most often used along with braces or other orthodontic appliances. While braces correct the position of teeth, orthodontic headgear—which as the name suggests is worn on or is strapped onto the patient's head—is most often added to orthodontic treatment to help alter the alignment of the jaw, although there are some situations in which such an appliance can help move teeth, particularly molars. Whatever the purpose, orthodontic headgear works by exerting tension on the braces via hooks, a facebow, coils, elastic bands, metal orthodontic bands, and other attachable appliances directly into the patient's mouth. It is most effective for children and teenagers because their jaws are still developing and can be easily manipulated. (If an adult is fitted with headgear, it is usually to help correct the position of teeth that have shifted after other teeth have been extracted.) Thus Headgear is typically used to treat a number of jaw alignment or bite problems such as overbite and underbite. Palatal expansion Palatal expansion can be best achieved using a fixed tissue born appliance. Removable appliances can push teeth outwards but is less effective at maxillary sutural expansion. The effects of a