Factors Contributing to Root Canal Failures

By Brian J. Gray, DDS, MAGD, FICOI

There are a variety of factors that cause root canal treatment to fail:

1. Many teeth have been treated endodontically using techniques that were considered state-of-the-art at the time of treatment but are outdated by today's standards. The good news is that root canal treatment rarely fails when there is proper diagnosis and treatment utilizing modern concepts, the best materials, and improved technologies and techniques. Additionally, better trained general dentists and endodontists can now successfully retreat many of the previously treated teeth that are failing.
2. Root canals generally fail because of leakage and bacterial infection. Bacteria may enter a tooth via three mechanisms:
   1. "Coronal leakage" results when decay and bacteria invade a tooth under a loose filling or ill-fitting crown.
   2. Bacteria may persist within the complex anatomy of the root canal system following prior root canal treatment.
   3. "Anachoresis" is a process in which bacteria from the systemic circulation are attracted to areas of chronic inflammation, such as can occur when a tooth is failing endodontically.
3. Root canal treatment may fail because of chronic "wear and tear" on the teeth. The mouth is a very harsh environment and teeth are subject to tremendous stresses. These stresses can compromise even the best dental treatment by causing teeth and fillings to crack and leak. If this occurs, saliva, which contains bacteria, can be introduced into the tooth and cause a well-performed root canal to fail. Endodontic treatment may also fail if a tooth fractures as the result of biting on something hard (ice, popcorn, a piece of bone, etc.) or from a traumatic accident.
4. Root canal treatment may fail due to an unforeseen procedural mishap. During any treatment procedure, an event may occur that has a potentially negative effect on the prognosis of the tooth. For example, if an instrument breaks inside the root canal space and the fragment cannot be removed, then treatment may be compromised. As another example, the root canal space may calcify and make canal identification and treatment difficult. In trying to find these small or restricted canals, an instrument may perforate the side of the tooth. These procedural mishaps can oftentimes be repaired using current techniques and materials. Infrequently, however, a procedural mishap cannot be adequately managed and root canal treatment fails. Every treatment has risks and mishaps may occur even when the best techniques are being utilized by the most skilled and experienced practitioners.
5. Endodontically treated teeth can fail due to periodontal disease. This disease can undermine and destroy the supporting structures of the tooth.

Even though root canal treatments sometimes fail, it is not a frequent occurrence when modern concepts, improved technologies, and current techniques are utilized for clinical treatment procedures. If a root canal treatment has not been successful, endodontic retreatment may be considered. Retreatment procedures have become increasingly predictable in successfully saving teeth.