Orthodontics is a specialty of dentistry that deals with the diagnosis, prevention and correction of malposition teeth and jaws. It can also focus on modifying facial growth, known as dentofacial orthopedics.Abnormal alignment of the teeth and jaws is common. Nearly 50% of the population, according to the American Association of Orthodontics, has treatment. Citation needed although this figure decreases to less than 10% according to the same AAO statement when referring to medically necessary orthodontics. Treatment can take several months to a few years, it involves the use of dental braces and other appliances to slowly move the teeth and jaws around. If the malocclusion is very severe, jaw surgery may be used. Treatment is usually started before a person reaches adulthood since bones can more easily be moved around in children. Orthodontics as a modern science dates back to the mid 1800s.Influential contributors to the field include Norman William Kingsley (1829–1913) and Edward Angle (1855–1930). Angle created the first simple system for classifying malocclusions, a system which is still used today. Until the braces were made by wrapping metal around each tooth. With advancements in adhesives it became possible to bond metal brackets to the teeth instead. 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 face bow, 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 alignments or bite problems such as overbite and under bite.