KMF gave a good and quick response, however some of the information wasn't entirely correct.
There are more specialties than were listed.
The 9 ADA recognized specialties are:
Dental Public Health
Endodontics
Oral Pathology
Oral Radiology
Oral Surgery
Orthodontics
Pediatrics
Periodontics
Prosthodontics
GPR (General pratice residencies) and AEGD (Advanced education in general dentistry) programs are NOT specialties, but they are comprised of Post-Graduate (PG) education, as are the dental specialties. These programs are also applied to just as are the dental specialties.
There are other programs that may be applied to (such as reasearch positions, or fellowships, or areas of interest), but these areas are NOT ADA approved specialties. Such areas would be anesth., or pain control, etc.