that wouldn't be ignorance, you using the word ignorance to say he doesn't know about mouth guards when he clearly does....... that's ignornace. Ignorance is not used to describe someone's follies.
Mouth guards do several things......... yes they help in a small instance of a concussion by preventing "chatter slam" which is an impact of the lower jaw into the upper jaw, usually happens if you get knocked out cuz you lose control of the muscle (rarely happens, unless you are unconscious). They also help with impact, again, to a certain degree. It will distribute the impact (spread) when it occurs. Overall a good idea, do you look like a puss, probably, but teeth are the thing that freak me out the most when i'm thinking of a new trick on a rail. Bugs me the fuck out.