The Collaborative International Dictionary of English v.0.48:

orthodontics \orthodontics\ n. (Med.)
   A branch of dentistry specializing in the treatment of the
   teeth so as to make the teeth align properly within the
   mouth; it usually involves fitting a patient with braces and
   sometimes oral surgery.
   [PJC]

WordNet (r) 3.0 (2006):

orthodontics
    n 1: the branch of dentistry dealing with the prevention or
         correction of irregularities of the teeth [syn:
         orthodontics, orthodontia, orthodonture, dental
         orthopedics, dental orthopaedics]