is a special type of dentist. He specializes in bringing teeth into what is called proper alignment
, although if you ask him directly he will probably cheerfully admit that most people don't have this, and it is based on the classical occlusion
Stereotypically, he will prepare braces for school age students, although a variety of other techniques are available, both for the genuine pathology and cosmetic purposes.
Unlike a medical doctor who is a specialist, he will also do most or all of the things that a general purpose dentist would do.
Source: My father the retired orthodontist.