by I am » Wed Jan 13, 2010 12:34 am
Chewing gum, if you chew a LOT at one time can be a good one.
If you want to take hits to the head, do work to strengthen the neck and if you wish to target the jaw in particular, you can tie a rope through a weight, or hang a weight from a towel, and then open your mouth and put the weight in there, then clamp down on it. You can then hold for time or get creative if you wish.