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 malocclusions severe enough to benefit from orthodontic 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.A typical treatment for incorrectly positioned teeth (malocclusion) takes about 1 to 3 years to complete, with braces being altered slightly every 4 to 10 weeks by the specialists called orthodontists. Orthodontists are dental specialists who are University-trained in the prevention, diagnosis and treatment of dental and facial irregularities. They provide a wide range of treatment options to straighten crooked teeth, fix bad bites and align the jaws correctly. Multiple methods exist for adjusting malocclusion. In growing patients there are more options for treating skeletal discrepancies, either promoting or restricting growth using functional appliances, orthodontic headgear or a reverse pull facemask. Most orthodontic work is started during the early permanent dentition stage before skeletal growth is completed. If skeletal growth has completed, jaw surgery can be an option. Sometimes teeth are extracted to aid the orthodontic treatment (teeth are extracted in about half of all the cases, most commonly the premolars).Orthodontic therapy can include the use of fixed or removable appliances. The majority of orthodontic therapy is delivered using appliances that are fixed in place,for example with braces that are bonded to the teeth with adhesives. Fixed appliances can have a greater mechanical control of the teeth and the treatment outcome is greater with the use of fixed appliances.Fixed appliances are, for example, used to rotate teeth that don't fit the arch shape of the other teeth, to move multiple teeth to different places, to change the angle of teeth, or to change the position of the root of the tooth. It is not preferable if the patient has poor oral hygiene (as that can result in decalcification, tooth decay, and other problems), if the patient isn't motivated (as treatment lasts several months and commitment to oral hygiene is required), or if the malocclusions are mild