Root canal treatment is done when infection reaches the pulp portion of the tooth. During root canal treatment, necrotic and infected portion of the tooth is removed and is then sealed with a filling material. If done with great precision and complete care, a root canal treated tooth can last lifelong. But in cases where root canal continues to harbor bacteria or irritants which keep the tissues surrounding the root of the teeth from being healthy (inflamed)even after the completion of the root canal treatment then the root canal treatment is taken to be a failure. Root canal failure signs and symptoms can occur month or years after root canal treatment. Pain occurs in root canal treated tooth in case of failure of root canal treatment.

Signs and symptoms of root canal failure include:

  1. Mild to severe tooth pain
  2. Slight to severe pain or edema in the gums neighboring the tooth involved can either be in a continuous or intermittent mode after the root canal treatment.

These signs can be persistent from the time of root canal treatment, be transient varying week to months or even be dormant for years making the tooth appear completely asymptomatic during this dormant period. In cases where the tooth is completely asymptomatic, the signs of root canal failure which show as persistent inflammation surrounding the infected tooth, can be identified by the dentist through the medium of x-rays.

Causes of Failure of Root Canal Treatment

1.    Shape of the Tooth’s Root Canals:  Sometimes the tooth may have root canal branches which are difficult to detect. The canals which are curved and branch out often go undetected at times. These undetected branches might be missed in the root canal treatment leading to its failure.

2.    Unexpected Number of Root Canals: There can be variation in number of canals which are present in the tooth. A tooth might have many small root canals also called as the accessory root canals which may be missed during the treatment. If a canal is missed during root canal treatment, then tooth can become infectious months or years after treatment and in such cases, root canal re-treatment is required.

3.    Bacteria in root canal:  Certain bacteria are very resistant in nature and no matter what it’s very hard to remove them therefore they easily escape the disinfection by root canal and infection persists.

4.    Cracked root: By root canal therapy, roots of the tooth become bit brittle and can fracture on chewing which can further cause failure of root canal treatment. Dental crown after root canal treatment prevents fracture of tooth on chewing. Fracture of the root may occur during root canal treatment procedure and cause root canal treatment failure. It is difficult to diagnose these cracks and these cracks can lead to pain later on.

5.    Breakage of file during root canal procedure: Accidental breakage of file during cleaning and shaping of canal during root canal treatment can cause infection in root canal treated tooth and failure of root canal treatment. If canals are sterilized and clean before breakage of file in tooth, then it doesn’t cause any symptom otherwise broken file in canal can lead to pain and infection later on. If file remains in canal before removing the necrotic pulp, then it has to be removed. File in unsterilized canals is to be removed before sealing the root canal treated tooth.  

6.    Defective or Incomplete Restoration: Defective or incomplete restoration at the end of root canal treatment fails to maintain a proper seal and this may lead to bacteria to penetrate back into the cleaned canal causing re-infection.

Inadequate filled canals and broken instrument in left lower incisor

7.    Gum Disease: The treated teeth are not completely resistant to tooth decay or gum disease so the tooth might be lost if proper oral hygiene is not maintained. If patient doesn’t maintain good oral hygiene, then abscess can occur years after root canal treatment and dental crown.

8.    Tooth Structure: The tooth structure which is damaged or broken as a result of treatment and which require restoration for stability which if not done can cause failure of root canal treatment.
The tooth filling even if accurately done at the time of treatment might break down with time due to some reason like high biting force which will again lead to seepage of bacteria into the canal and re-contaminate it

Success rate of root canal treatment is 95%. In about 5% of cases, complications may occur after root canal procedure which can lead to failure of root canal treatment.   
To avoid further infections after getting root canal treatment and dental crown, it is important that patient maintains good oral hygiene and get regular dental check ups done.

Treatment after Failed Root Canal Therapy

In case of root canal failure, re-root canal treatment, Apicoectomy or tooth extraction may also be required to remove the infection from the tooth. Dentist will evaluate the condition of the tooth and will decide that whether tooth can be saved or not. If he thinks that prognosis of tooth after root canal treatment or Apicoectomy is not good, then he will pull the tooth out. If tooth extraction is required, then missing tooth can be replaced with dental implants, dental bridges or partial dentures. Dental implants are the best option for replacement of missing tooth.   

Dental Implants after Tooth Extraction   

Root canal retreatment can be done to save the tooth and tooth and remove the infection in root canal treated tooth. Procedure of root canal re-treatment is somewhat similar to root canal treatment and is mainly performed by an endodontist who is specialist in performing root canal procedure.

Apicoectomy that is surgical removal of root apex may be required to remove the infection from the tooth. To seal the root, small filling (retrofill) is used.

Bone Removal for Apicoectomy

Success rate of root canal treatment is not as high as root canal treatment done for the first time. Root canal treatment success rate is 50%-75%. If re-infection occurs after root canal re-treatment, then tooth extraction may also be required.

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  • keith stevens

    keith stevens 22 - August - 2015, at 13:23 PM

  • I had my semi-annual cleaning and this is the time they take x-rays but this time they decide to take one of the front lower teeth. I have gone to the same dentist for 10 years and they are awesome but this is first time they did an x-ray in the front. They noticed a shadow below a lower front tooth. I had a root canal 30 years ago and have not had any pain or swelling. They tapped the tooth and checked the gum area but I did not feel any pain. I was referred to another doctor and he told me the pin they used was too long and would break the tooth if taken out. The doctor told me the tooth was in good condition. He told me I needed to get a re-treatment to get the rest of the root out and then back fill the tooth. Will this solve the chronic infection below the root?

  • dr apinder

    dr apinder 25 - June - 2014, at 06:32 AM

  • hello tony this is also the method of rct so dont worry...

  • Erik

    Erik 20 - February - 2014, at 22:49 PM

  • If a Root Canal Treatment isn't successful, due to a portion to the root being left behind, is the re-treatment of the affected tooth normally the responsibility of the the Doctor who initially did the root canal? I had a root canal done on #7, and approximately 4 months later I had symptoms of an abscess(I've had half a dozen of them, so by now I can usually tell when the abscesses are just beginning) and upon consultation with my Endo an apicoectomy was performed on said tooth. My question is would it be reasonable or off base for the doctor who perform the failed RCT to pay for the apicoectomy or at least a portion of it? The RCT was performed by a doc(not the Endo), and my Endo hinted at the fact that the retreat should be at least partially paid for by the original Dr. The Dr from the original treatment does not believe that he should be responsible for the failure of the RCT. I do understand that things go wrong and they can't always be avoided, but with any other service if there was a mistake then the person who messed up should help rectify the situation. Between the $1000 for the original RCT, and the $1400 I had to pay to fix the RCT failure, I feel like this is ridiculous. If a mechanic messed up on fixing something on my car, then I would expect him to fix it or at least not charge me for the cost of fixing the mistake.

  • Rita

    Rita 27 - December - 2013, at 09:12 AM

  • my boyfriend had a root canal #14 for chronic pain in the tooth, not for an infection. it was not successful and the dentist recommends a cap? is this a good solution

  • Dr.Ritz

    Dr.Ritz 02 - May - 2013, at 20:14 PM

  • Hi Dennis, Re Root Canal treatment is a normal procedure done for infected tooth which is already root canal treated. However the prognosis is not that good as it is with first time root canal treatment. For the success of re treatment the case selection is good. If your Endodontist say that you need it then you should go ahead with this.

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