Why do your teeth hurt when you scuba dive?

Diving at depths increases pressure as you go down and decreases as you head for the surface. Any air pockets in your body will contract and expand as you do this unless you can "equalise" the pressure (pressure in the airspace = pressure outside airspace). If you have cavities in your teeth, air trapped can expand as you go shallow which could cause pain. Also, the water that inevitably touches your teeth can be cold and sensitive teeth won't like this. Another cause of dental pain, more noticibly jaw pain, is caused by biting the mouth piece too hard, usually due to anxiety or a poorly fitting mouth piece in the regulator