We didn't allow teeth on us either. But, he constantly came back with his nipping on our hands. It was like a "have to," greeting behavior. We even used the hand (the whole hand) down his throat, as a negative result from nipping. It did have some good results. But, he would just let you do it and then nip the next time.
Because of my RA, I cannot have a dog that is not compliant or who is ever rough with me. If Tinker the Wonder Puppy is ever not compliant with me, then he will have to go. I gave him to Hub as a birthday present, but he is submissive to me as well. I think a good part of it is the attitude I have, whether I deeply love him or not, that he WILL behave every time, no exceptions. Of course, we're clear about what we want.