One of our patients recently asked this question. The most common occurrence is when an old silver amalgam filling begins to corrode. All amalgams eventually break down since they are a metal filling in a wet environment. They break down by separating away from the tooth at the junction of the enamel and the metal. When this happens there becomes a microscopic leak that allows bacteria to enter into the space between the tooth and the filling. Once there, they grow protected and quickly undermine the filling as they eat away at the tooth under the filling.

This particular situation leads to a lost filling, a toothache and possibly an abscessed tooth. It can take a few months to a few years for this to occur. It’s always best to replace a filling when it appears that this process is beginning to happen.