i used to bite my nails, until my thumb nail got infected and i had to have the nail sliced off, not nice, the bandage was huge and it still hurt if i knocked it. 6 locals to numb it enough, i still felt it, and the nurse doing it just had to bite the bullet and get on with it cos i was getting antsy.
certainly cured me, never bit them again. now i have to cut them regular or i cant type

try growing one, that's what i've recommended to friends with the same problem, one at a time, i bet when you get to the 3rd you'll have weaned yourself off the biting

chell
x