L.W.
Good suggestions thus far....other ideas are roaring like a lion, or pretending tooth brush is a choo choo train, and teeth the tracks.Making EEEEE with teeth clenched for front teeth, ahhh,or the roar for inside..We have Baby Einstein where puppet goes Bleh, so we do that and brush tongue.
My older son gets sensitive to touch. I found that he was resistant mainly because I brushed too fast.I find I need to be good example and be doing it together with the kids. If they don't see me doing it when I do it alone, they do not know and do not emulate the behavior.
My now 2 year old liked being held on my lap and hung upside down...
Hope you find something that works.
L.