I grind my teeth at night. I've ground down a couple of my teeth, but thankfully not to the point where they need to be replaced. My dentist and I spoke about it and he told me they could mold a night guard, which would take time and cost a decent amount, or I could go out and pick up a regular sports mouth guard for like 2 bucks. I went for the 2 dollar mouth guard. It just needs to be replaced every 6 months or so, but it is a lot easier and I have a mouth guard around if I play some hardcore ball.
I don't know if there are any underlying causes for grinding, but I know my father grinds his teeth too. Maybe its a genetic thing. Or maybe both of us just have a lot of stress from all the stupid people in the world. Damn you stupid people!!