I know some people who wear mouth guards.
Others wear full PB masks.
Some people just keep their shemaghs up tight around their face.
Some people opt for the stronger material balaclava style face masks.
Some people wear just plain old balanclavas.
Myself, I wear nothing, Ive considered wearing a mouth guard, but have never ever actually dont it, and I have been shot in the teeth a few times, with no breaks as of yet, luckily.
Aside from the methods I listed, human ingenuity is your best shot at commining up with something to protect your chompers.
"Its only a little bit on fire"