division of dentistry dealing with the prevention and correction of irregularities of the teeth—generally entailing the straightening of crooked teeth or the correcting of a poor bite, or malocclusion (physiologically unacceptable contact of opposing dentition, which may be caused by imperfect development, loss of teeth, or abnormal growth of jaws). Of significance to the orthodontist is the sequence of eruption (emergence of the tooth from its developmental crypt into the oral cavity), because such knowledge helps to determine the position of the teeth. Human bone responds best to tooth movement before the age of 18, and consequently orthodontic work is usually more beneficial to a child than an adult.

The practice of orthodontics has existed since early antiquity, but the more elaborate methods of treatment came about in the 20th century. Orthodontics quickly became a specialized branch of dentistry with its own professional organization. Training in orthodontics usually consists of a two-year postgraduate course.