And then there are some programs that don't like general dentists because of the 'break in' period and the easy ability of the dentist to leave and rejoin their private practice world. Intern years are better to improve the application. Just hearsay though. The other dental specialties are different though.
I would plan on working hard in dental school, applying during dental school, and matching immediatly. Working for a couple years would be torture if you really do like OMS enough. You will see what I mean when you get to the application, match, acceptance point. OMS is a dental specialty, but the day to day of oms residency is far removed from the dental world.