Frequently, we find a tooth that has an old defective filling (it has a crack or large fracture) and we recommend that it be replaced. Regardless of the type of restorative material that is used to replace the old filling, the tooth sometimes, in a few days or weeks, becomes sensitive to temperature, or chewing, or just aches out-of-the-clear-blue. The patient returns somewhat upset that the tooth felt OK before the repair, but now, it is bothering them quite a bit. What happened?
The dentist does not always know the exact "health status" of the pulp of every tooth he or she restores, especially when an x-ray shows no obvious problems and the tooth was not sensitive prior to the recent restoration. However, the pulp (nerve) of the tooth could be in a weakened state from previous restoration(s) and drilling on the tooth just one more time could push the pulp "over the edge", and cause the pulp to die, or abscess. The more times a tooth is drilled on, the greater the likelihood of an eventual abscess. There is no way any dentist can predict how many times a tooth can be filled and refilled before, if ever, it abscesses.