noun
The dental specialty concerned with correcting irregularities of the teeth and jaws, often using braces or other appliances.
彼女は大学で歯科矯正学を専攻している。
She is majoring in orthodontics at university.
歯科矯正学の進歩により、治療期間が短くなった。
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.