Failing Root Canals


Once upon a time you had a toothache. You were told that the nerve was dead or dying and, in order to save the tooth, you would need to have a root canal. This procedure removes the nerve that had lived inside your tooth, cleans the space out well, and places a special inert root canal filling material inside the tooth.  And, the pain goes away so you assume the procedure worked.

A few years go by and the tooth hurts again, or the dentist finds a problem on the x-ray, and you are told that the root canal is now failing. Definitely not the news you want to hear.

So, what could have caused that problem? Something may have happened during the root canal procedure. If the canal cleaning did not go far enough down the canal and left some of the tissue inside the canal, the bacteria can cause a failure. Another possibility is that there was an extra canal somewhere inside the tooth that the dentist could not find, and the tissue still there is now causing a problem. Sometimes there is not enough irrigation of the canal to remove all of the nerve tissue and that could come back to be a problem. Another situation is when the canal system has an unusual anatomy (like a 90 degree turn) which cannot be detected in a 2 dimensional x-ray.

There are some other possible causes. If the patient waits too long to have their temporary replaced with a permanent filling and/or a crown, the temporary can leak, allowing bacteria to go down into the space.

There is another case of operator error. If the root canal specialist accidentally goes outside the root canal space and into the surrounding tissues, the result can be a disaster or near disaster. Sometimes the perforation, as these situations are called, can be treated by placing a material that is compatible with the surrounding tissues. More often the tooth is no longer salvageable. I have noticed a similar failure when a restoring dentists places a post but is not careful of the tooth anatomy and goes outside the confines of the root.

Another failure of root canals comes from fractures. If there is some significant amount of tooth missing a crown is generally recommended to help strengthen the weakened tooth. However, not everyone is aware that the crown procedure is recommended, and the tooth fractures. On rare occasion I have seen a tooth fracture on the roots under the crown. This condition is not salvageable, and the tooth must be extracted. The tooth is then replaced by current methods to get a new tooth (implant, dental bridge, removable partial denture).

For the best outcomes, I recommend that my patients see a root canal specialist for their root canal treatments, especially the molars. Molar root canals can be tricky because they are hard to get to, the canals can be narrow and curved which make it difficult to treat to the end of the root. The root canal systems in anterior and premolar teeth are generally straight and much easier to do.

I recently spoke to one of my root canal specialists who told me that 70% of his treatment is treating another dentist’s failed root canal. I thought this was an astounding statistic! And retreatments are successful only 60-65% of the time with no guarantee – a lot of money to spend for another treatment with not excellent chances for success. For this reason, many dentists would recommend an extraction and an implant when this situation arises.

I want to mention 2 surgical options that may work in select cases. One is called an apicoectomy. This is usually done on upper front teeth where there is still a large lesion (radiolucency) at the end of the root despite a root canal that looks good radiographically. In this case the end of the root is surgically accessed, the end of the root is cut off, and a filling which is inert is placed at the end of the root , and the soft tissue that is around the tooth (where bone is supposed to be) is cleaned out. This procedure works out pretty well. Another surgical procedure happens on a molar where one of the roots is hopeless but the rest of the tooth looks fine. It is called a tooth hemisection, and the affected root is removed after a root canal is performed and a filling is placed at the point of hemisection. Even with success, the average success of this procedure is only 6 years on average. With the current success of dental implants I have seen very few of this procedure in recent years.