In order to become an orthodontist, an additional 2-5 years of schooling will be required in the science of orthodontics plus a 2-3 year residency at an ADA approved program.ow to become an Orthodontist. In order to become an orthodontist, prospective students must first become licensed to practice as a dentist. There are over 56 dental schools in the United States that are accredited by the American Dental Association (ADA).