Why do teeth sometimes hurt or need root canal after a filling?

This crops up a lot on the forum. A poster gets a filling that remains sore, gets sore after a filling. The natural response is to think that the filling is causing problems.

The truth is that when decay is in a tooth, or has a large previous filling. The nerve can get inflamed. Removing the soft decay and filling the tooth can allow the nerve to settle most of the time. However sometimes the toxins from the decay will irreversibly inflame the nerve and cause pain or discomfort. The solution is often a root canal, to remove the problem nerve.

Dentists are always trying to repair damage. They cannot replace a malfunctioning or infected nerve. The best solution is to prevent decay through restriction and frequency of sugar intake and regular home and professional cleaning. Dentists will often try a filling to try and avoid you the patient having the time and expense of a root canal, but if it does not work the cause is the decay and tooth damage.