Well, I was going to let you know that Dr. Yates would be here, and hadn't forgotten you - it was a long weekend with several emergencies - but looks like we have a wonderful new volunteer :) Welcome!
I was also going to try and clarify something. I agree that this does not sound like something that would occur with teeth grinding. However, I think your horse is indeed cribbing, but you aren't clear on the meanings...
You have wood chewing which is just as it sounds, the horse chews and strips off wood. This is rough on your barns, fences, trees and your horse and can mean several things - boredom, nutrition deficit, etc.
Then you have cribbing, which is also called wood-sucking, or in some circles, wind-sucking (but in fact, wind-sucking is a totally different thing...). This is normally done with the horse biting onto something solid and then "sucking" wind. The action causes a release of a natural chemical into their brain and stimulates a natural high. Problem is, this isn't all that good for the horse, and can cause teeth damage and other problems, including becoming so "addicted" that they will not eat as they should.
Now, MOST horses that do this you will see damage to the upper front teeth, not lower, but I wouldn't rule it out becuase of that. I have one horse who figured out he could do it without biting down on ANYTHING. He instead can put his head in a secure bucket and pull back....its a very strange thing. Needless to say, he no longer gets a bucket on the wall!
What I would do is as the other poster suggests, get a veterinarian out who knows his equine dentistry. Make sure there's not something else going on. I'd also make a point to try and observe what your horse is doing. This may take time and patience, and possibly even a bit of ingenuity if he's prone to performance jitters! In fact, if you or a friend has a short circuit camera or even a long lasting video cam, I'd put that to use. Is he cribbing? If so, on what? It might be that something in his stall could be removed and he'd be fine. Or it might be you need to invest in a miracle collar. Is he rubbing his teeth on something in the stall? A weird habit, yes, but I've see it done...
Good luck! And you might want to check out our Equine Health and Behavior board, we have question over there dealing with cribbing...
PH Cody
HorseHobbyist Community Director
