Ok, you are now a dentist. You have completed four years of dental school and have "Dr." in front of your name. Congratulations! At this point you can do almost any technique, diagnosis and treatment modality in all of dentistry. What if you want to specialize? You know, be an Orthodontist or Oral Surgeon? That takes more years of study as seen here in a this graphic. Most specialty programs are at least two years in length. There are some variations in programs from one school to another. For instance, some specialty programs in Orthodontics are two years and others three. GPR programs are usually one year in length.
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*Compiled from data from the ADA Survey of Advanced Dental Education 2010-2011, and published in the ADA News Volume 43, No. 13 July 16, 2012.