Late time, my BB also didn't let me brushing his teeth. I've got one very good method. You give him your toothbrush and then you two brush each other, my son loves this practice so much now.
By the way, I use pigeon toothbrush, with the kind of plastic toothbrush rather than the one that the adult use, coz, it seems softer and my son let me to put in the toothbrush at least.
Try it.