Don't get shot. Keep your mouth closed. It works lol
CQB, I wear a lower mesh. The odd outdoor skirmish with lots of unknowns or noobs I wear the mesh too. Milsims, where I know most of the guys, the keep your mouth closed technique works well when you can't avoid getting shot.
Quite a few people wear mouth guards and they save teeth but it's ridiculous and a pita listening to them over comms!