An orthodontist is a dental specialist who treats mal-aligned teeth in children, adolescents and adults. He/she also treats dentofacial deformities in children.
Orthodontists are dentists as well. They have gone to four years of college and attained their under graduate degree. From there they go to dental school and earn a D.D.S. or D.M.D. degree.
After dental school, a dentist enters an orthodontics residency which is affiliated with a dental school. Residencies last from two to three years. Commonly, the resident not only receives a certificate in orthodontics, but also a Master's Degree.
As such, orthodontists are not only members of the American Dental Association (A.D.A.) but also of the American Association of Orthodontists (A.A.O.) as well. Orthodontists do not practice general dentistry.