orthodontics

n [sing v] (medical 医) (branch of dentistry that deals with) preventing and correcting irregularities in the position of the teeth and jaws 正牙（学）.

originally, originate, originator, oriole, ormolu, ornament, ornamental, ornamentation, ornate, ornately, ornateness, ornithological, ornithologist, ornithology, orotund, orphan, orphanage, orris-root, orth(o)-, orthodontic, orthodontist, orthodox, orthodoxy, orthographic (also orthographical), orthographically, orthography, orthopaedic (also orthopedic), orthopaedics (also orthopedics), orthopaedist (also orthopedist), ortolan, oryx, OS, Oscar, oscillate, oscillation, oscillator, oscillograph, oscilloscope, osier, osmosis,