Teeth that have had a root canal, or endodontic treatment, should last as long as other natural teeth. The success rate is over 90%, but occasionally a tooth that has undergone treatment fails to heal or pain continues despite therapy. Healing is often times dependent on the success of the final restoration. It is very important to have the tooth properly sealed over the root canal to guard against contamination by oral fluids and bacteria. Often times a permanent filling will be placed by the endodontist, but the referring dentist usually completes the final seal or crown over the root canal.

Non-surgical endodontic therapy may fail for a number of reasons other than contamination. Some teeth may have complex anatomy which makes endodontic treatment very difficult. Curved or narrow canals, or canals that have been blocked by prior treatment may lead to possible complications. If a permanent restoration or crown is not placed within an appropriate time following the procedure, there is a risk of tooth fracture.

In endodontic retreatment, an opening is made on the chewing surface to reach the filling material. This is removed and canal system is cleaned, disinfected, and resealed. An attempt will be made at that time to determine the cause of failure.