“How many times can you have a root canal on the same tooth?”

The same tooth can need and have root canal treatment more than once. The seal at the end of the tooth can fail and a reinfection can occur years after the tooth is first treated successfully. If a previously treated tooth becomes reinfected and if the tooth is savable (not cracked or decayed), retreating the root canal is the treatment of first choice.

Not all root canals are successful since the anatomy within the root can be unpredictable. In that case, usually a re treatment, followed by a surgical apicoectomy or tip of the root removal makes a total of three attempts to save a typical tooth. At that point, extraction and replacement may be the most likely procedure to succeed.

If all the roots are DETECTED and treated PROPERLY, once is enough. Sometimes a tooth might have multiple roots beyond expected, and they go untreated and asymptotic for years. But they can act up some time later and necessitate root canal therapy for a second time. Also, other factors may cause a re-treatment of the same tooth.  

Hate to say it, but it all depends - on how many roots and the way it may have been done each time. And, what is the reason for having it done multiple times? If it is necessary because of recurring infections, then each time the surrounding bone is affected and possibly weakened. Older methods of treatment were more invasive and often removed more tooth and root structure than today's more conservative methods do. Multi-rooted teeth inherently have thinner roots than most single-rooted teeth. Each time a tooth is treated with root canal (endodontic) therapy, there is a chance that the structure of the tooth is weakened further. Due to the physical nature of treatment and also the fact that there is no longer a blood supply in the tooth, root canal teeth are physically weaker and more susceptible to fracture. Teeth with prior large restorations almost certainly require crowns to prevent the chewing part of the tooth from breakage, but even so, there is a chance for root fracture in the future. Often when a properly-performed root canal needs retreatment, it is an indication of root fracture, which is most likely the end of the line for the tooth. That is why I always tell my patients the pros and cons of root canal therapy versus implants. Though I have personally seen poorly-treated root canal teeth last in excess of 45 years, that is not too common. Implants have a higher success rate over that amount of time. In the short run, root canal treatment with a crown is less costly than an implant, but not dramatically so, and the longevity is often less. Each time retreatment is necessary, the odds of long-term survival drop substantially.

Michael A. Conrad, DDS, PC

A root canal can be retreated. These days having a 3D X-ray of the tooth to try and determine why the root canal failed is the state of the art. The 3D image can show problems that are not visible on regular 2D X-rays. Some of those problems cannot be treated by root canal.

A root canal can be done multiple times on a tooth, but at a certain point, the benefits may be far less than the negatives so extraction should be considered.

Usually only once, but sometimes a second, but rarely a third. 

In theory there is no limit

Generally a root canal only needs to be done once on a tooth. But as many times as necessary to clean out all the canals and remove all the infection present in the tooth.