Have you been accepted to a program?
Some programs will require a full license for the state you're doing your residency in. The rest will require a limited license where you don't need to take the regional boards.
I would suggest getting it done while in dental school as it is easier to get patients and you have a lot of free time.
If you wait until you're an OMFS chief to take these exams, it'll be years since you did your last filling, getting patients is extremely hard, and you don't want to use your limited days off to tackle this exam.
Just keep your license active in the State you are planning to practice in, and if you decide to go somewhere else, many states will allow reciprocity.
