Cosmetic dentistry is not a legally recognized specialty, so any dentist can claim to be a cosmetic dentist. Cosmetic dentistry is more an art than a science. While a good cosmetic dentist may get additional training, none is required. If you only want to be an assistant, you will need to attend a dental-assistant training program and be versed in dental terminology. To actually become a cosmetic dentist, you will need to go to a dental school and, generally speaking, complete a four-year degree program. You will then need to take the Dental Admissions test and apply for admission into dental school.