This latest Airsoft Medicine video you should watch (no, not about the mouth of Dr. Airsoft) as this type of protection is one the least priorities by airsoft players who don't use any lower face protection when playing airsoft only to find out it's going to be an expensive trip to the dentist after they're caught by a BB with their mouths open. Highly recommended video.

"Dr. Airsoft of Airsoft Medicine compares the ProTech Dent dental guard to a custom guard made by Dr. Kihara, DDS, and an off-the-shelf 'boil-and-bite' style sports dental guard by shooting at them with an airsoft gun. He finds that the custom-made guard by a dentist provides superior protection and comfort. These do not provide soft tissue protection for the nose, lips, and cheeks as a lower face or full face mask would."