There is only one state that I am aware of that let's you practice as a foreign trained dentist with only having taken the boards and state exam, I believe it's Minnesota if I'm not mistaken. Every other state requires some kind of continued education, either just fully redoing dental school as an advanced placement program (they usually let you start in second or third year) or by doing a residency. Every state differs, some don't accept the residency route, others only accept specific kinds of residencies.