I hear you. I knocked a big chip out of a front tooth when I was a boy. I had a partial installed, and have knocked it out near a half dozen times. I have never knocked myself silly with weights, but have had many near misses that made me think a mouth guard may be a good idea.
I went to WalMart and bought a $.97 football mouth guard. You boil it, then form it to your top teeth. Cut off the front strap, and you are set. You don't want that nasty thing sitting around, so ask your friendly neighborhood orthodontist for a retainer case. I got one for FREE.
I don't wear a guard all the time, but it seems like a good idea when projecting Dumbells toward your mouth.