I agree with AshDawn. Those mouthguards are LIFESAVERS! I have one that I got at Walgreens. You just boil it, and then put it in your mouth so that it conforms to your teeth. I think the thing was about $25. Using this has really reduced my migraine frequency AND the jaw pain.
Check out this link:
http://www.dentalconcepts.com/html/nightguard.html