The dental specialty concerned with correcting irregularities of the teeth and jaws, often using braces or other appliances.
She is majoring in orthodontics at university.
Advances in orthodontics have shortened treatment times.
Refers to the actual correction of tooth alignment (the treatment), while 歯科矯正学 is the academic discipline.
Compound of 歯科 (shika, 'dentistry') + 矯正 (kyōsei, 'correction') + 学 (gaku, 'study'). A straightforward modern academic term.