pliances for Correcting Irregularities of the Teeth. Angle's work strongly influenced the development of orthodontia in the United States, which diverged from its evolution in Europe. The terms orthodontia, orthodontics, and orthodontistry are primarily applied to the specialty as it is practiced in America; the more common term in Europe is dental orthopedics, since European practice stresses the appliances used by practitioners.
By the late 20th century, dentistry had developed a number of precise specialties, including endodontics (root canal therapy), periodontics (treatments of the gums), and orthodontics. Orthodontics grew out of the findings that teeth and the bones of the jaw in which they are set are not absolutely fixed in place. The shape of the jaw can be changed as it grows, especially during adolescence. Teeth can also shift position; dentists discovered a phenomenon known as the anterior component of force, in which teeth, which are naturally tilted slightly forward, have a tendency to move forward to keep in contact with the next tooth in front. Orthdontic techniques were developed to make use of these factors in correcting some of the problems which can develop in the positioning of teeth in a patient's mouth.
Because teeth can grow faster than the mouth in which they are positioned, orthodontic problems frequently develop during the growth spurts of adolescence. Some experts estimate that as many as 70 percent of all individuals require some form of orthodontic treatment, but Jay W. Friedman (1991) cautions against trying too hard to achieve perfection: "Not every crooked tooth needs straightening" (p. 9). He argues, "Malocclusion is not a disease. There is no convincing evidence linking crooked teeth to decay and periodontal disease" (p. 120). W. J. B. Houston and his colleagues (1992) agree: "There is now increasing evidence that not all malocclusions should be treated . . . and that specialist sk...