The test is pretty poorly written in my opinion. They asked very few questions about dentoalveolar, trauma, anesthesia, TMJ and orthognathics and a lot of questions about split thickness skin grafts, free flaps and cancer. This is fine if you are in a program that has a lot of these kind of patients but the majority of OMFS programs do not. I even got a question about balding pattern classifications!! It is just an example of how our specialty is trying to forget its roots. There is a push to get away from being the dentoalveolar experts that we are training to be and become extremely broad scoped. More power to you if that is your interest but I don't think that it is very representative of the majority of an OMFS residen't knowledge and interest.
So with that said, study stuff that you don't think they would ever ask. I do not remember many repeat questions but I do remember thinking, "Oh, I probably should have studied that stupid crap I thought they would not emphasize"
I ended up doing OK on the test even though I felt pretty clueless about a lot of the questions. I spoke to a friend of my that is at a different program and he felt the same way.