When root canal treatment works, it is a great treatment--a great way to save your tooth. However, in about 5% to 15% of the cases, a root canal or endodontic treatment will have failed.
Root canal treatments do not wear out. Once they're a success, they're a permanent success. But there is always a possibility of failure--things can go wrong during endodontic treatment that won't become apparent for a long time after the treatment is completed.
Things that can lead to root canal failure:
The root canal system of your tooth can be complex. One of the most common reasons for failed endodontic treatment is that there is an extra canal in the tooth beyond what would normally be expected. Lower incisors, which are "supposed to" have only one canal, can have a second, hidden canal hidden behind the first one. Molars with three roots can have four canals. If the extra canal isn't found, it will eventually become infected and there will be treatment failure, resulting in a tooth abscess.
There may be an obstruction that prevents the dentist from cleaning the entire canal of your tooth.
There can be extra canal branches deep in the pulp system of a tooth that can be difficult or even impossible to reach with a dentist's instruments.
There can be a mishap during the endodontic treatment, such as a broken instrument that becomes lodged in the canal (read Dr. Hall's blog post about a broken root canal file), or problems in getting the filing instruments to move around curves. In the process of instrumentation, ledges can develop that can make it very difficult to complete the treatment.
A root of the tooth can develop a crack which makes it impossible to seal the canal and prevent infection from re-entering the tooth. Read more about fractured teeth.
Treating a failed root canal:
For many of these problems, re-treating the tooth may solve it. The dentist can go into the tooth, remove the old endodontic filling material, and then re-fill it, getting a better seal the second time. Or the dentist can send the patient to an endodontic specialist who has special tools and techniques to deal with failed treatment.
Sometimes, pain after a root canal can be difficult to diagnose. Kathi from North Carolina shares an experience she had with this.
The chances for a successful treatment are always the best the first time it is treated. In the case of a failed root canal, the chance that a re-treatment or surgery will succeed is going to be 50% to 75% at best, depending on what is wrong.