Orthodontics, 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 age 18, and consequently orthodontic work is usually more beneficial to a child than to an adult.