One should seek out a biologic dentist who is familar with this approach. A simple way to locate one in your community would be to contact all the health food stores for recommendations of the best mercury free dentist in the area.
Already Have a Root Canal
If you already have a root canal you can contact Dr. Pendergrass at the University of Kentucky for a kit that can assay to see if the there are organisms present in the tooth which are secreting potent toxins.
If the tooth is infected with significant pathologic bacteria there are several options. The simple one would be to have the root canal redone with a material called Biocalex.
Biocalex actually destroys many of the organisms and is far less likely to cause problems in the short run. If this fails and one is seriously debilitated it maybe necessary to extract the tooth.
Dentist Tells You You Need A Root Canal
If you are not seeing a biological dentist already try to find someone who understands this process. That would be the first step. Many biological dentists have alternatives, such as infra-red lasers, that can save the tooth in about 25% of the cases.
If the tooth is dead and there is no way to revive it, then it would be best to have a root canal with Biocalex.