K.R.
My kids think it is SO fun to pretend they are at the dentists office. They are both reluctant brushers (my son was a fighter at age three too), but this brings them running to the bathroom every time!
I sit on the toilet seat and they (one at a time) sit across my lap. They lean back and open wide and I brush while making a sound like the electric brush at the dentists office. I also ask questions like a dentist would, like "have you been brushing twice a day? these teeth look great! I'll give you some floss to take home with you today, tell you mommy I'm very proud of you! Can't wait to see you back at my office tonight :)"
My kids are really into make believe and they just think this is so funny that I pretend I am a dentist. Some nights I am not in the mood, but really I prefer to do this because I make sure to get all their back teeth and am able to do an inspection of my son's two capped teeth (due to bacteria not getting brushed well enough when he was three) BTW, they are 3 and 6 years old.