Back in the 60s or 70s my mom was doing clinicals for dental hygiene at a local mental hospital. There was a patient that was admitted because he had gone insane and clawed his top lip and nose off. No one ever tried to figure out why this man's sanity left like flipping a light switch. Turns out he had a second set of top four front teeth that had not come through, got infected somehow, and it was so painful it drove him insane.