In the simplest terms possible, a root canal is designed to remove the inflamed or infected contents of the root, in its entirety and make an airtight/watertight seal to prevent bacteria from re-entering. Then when the tooth is restored properly, the tooth should last a lifetime.
Endodontists routinely treat the more complicated anatomies of molar root canal configurations. Other types of teeth that should be treated by Endodontists are calcified, long and curved canals. When dentists treat these cases we often have to correct instrumentation errors, cleaning deficiencies, file separations and perforations. Although Endodontists can correct these situations, it is always cheaper and ideal to treat the root canal right the first time.