Not trying to be snide or anything, but you may want to browse some of the past discussion in the Diving Medicine forum, if you haven't already. Teeth seem to come up every month or two. In fact, you may want to ask a mod to move the thread over there, where people with more expertise in the area may be more likely to lurk.
However, off the top of my head, some possibilities that have been discussed before include:
- Air in a pocket behind a filling
- Crack in tooth or cavity, resulting in air ingress
- Nerve in need of root canal (possibly another air pocket)
- Temperature sensitivity
- Sinus problems (infections, blocks, etc.)
I'm no expert in the subject, so take this with a grain of salt.
Some things to consider (which may help any discussion here):
- Which tooth (front, molar, upper or lower)?
- Is this a recent change? How much diving have you done before with this tooth?
- Any recent dental work? Cleaning?
- How knowledgeable about diving is your dentist? Some people feel this can make a difference.
Best of luck.