As was already mentioned the yelp and the ignore tactic worked well for me. What I would do is yelp like they really hurt me, this gets them to stop and they start licking my hand as if to say, "Sorry Momma, we forgot we weren't playing with Daddy."
Daddy is their favorite chew toy.
The other thing that works well is I'll say Quit! drop the toy, stop playing with them, turn away and ignore them for a moment. They can't stand this and will bring the toy around to me. I'll play with them again, until they bite me again and then do it all over. It didn't take them but a time or two to figure out just what was good behavior and what was bad.
Just be consistent, every time their teeth touch you, you must stop the play. Good luck!