Failed Root Canal Treatment: Symptoms and Causes

Last updated on August 20th, 2019

What Is A Failed Root Canal?

A root canal is a dental treatment to repair and to save a badly damaged tooth or an infected tooth with cavities. The procedure involves in the removing of the damaged area of the upper tooth, pulp, cleaning and disinfecting the region and then filling and sealing it with a cap. The term “root canal” comes from cleaning of the canals inside the root of the teeth.

However, roughly five to fifteen percent of the root canals performed fail.

root canal treatmentThe procedure essentially fills the interior of a tooth with a filling to the root. Failure does occur however, there is a retreatment procedure that can remedy the situation before bacteria can form and develop into an infection further damaging the tooth.

Failed Root Canal Causes

There are several reasons why there can be a problem at the root of the tooth. Here is a look at the most common failed root canal causes:

The Entire Root Canal Was Not Cleaned

Canals located in the tooth root can be curved in shape and the smaller ones are not easy to see properly. Even with a high success rate, a standard root canal procedure can leave behind a collection of sticky bacteria colonies known as biofilm. This can be difficult to remove from the root canal system. When it is not completely removed, the bacteria left behind can grow and develop into an infection.

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Dental Crown Failure

Bacteria can re-enter the root canals when a dental crown used to protect the tooth fails. Failure of a crown can be in one of several ways and usually is when it cracks or breaks.

dental crown failure: cause of failed root canalThe crack or break in the crown exposes the interior of the tooth to infection as bacteria will have a direct route to the inside of the tooth that had the root canal treatment.

New Infection

The root tip may be sensitive and as a result become susceptible to the formation of an infection from another source within your mouth. If the area around the affected tooth was not thoroughly cleaned the conditions may result in a new infection developing.

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When a new infection develops, it can invade the tooth quickly and create a number of additional oral health problems.

Inner Seal Breakdown

The inner seal that went inside the tooth during the root canal can erode over time. When this happens, bacteria can invade and develop into disease. The inner seal acts much like a coating, protecting the walls of the tooth from the inside.

When that seal fails, it gives bacteria places to take hold and grow into infections.


If a discharge takes place around the tooth there may be another infection and a possible abscess forming. Your dentist may recommend retreating the tooth as a result.

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The abscess may be adding pressure to both the tooth root and gum with the discharge being fluids that have no other way to escape.

Can You Die From Leaving A Root Canal?

If the root canal is required to remedy an abscess and is not performed, the abscess will continue to grow. The growth of this infection will work its way into your bloodstream. Septicemia, or blood poisoning, will occur. Left untreated, it may lead to death.

Symptoms of Failed Root Canal Treatment

There are several main signs of a failed root canal. They include the following:

Ongoing Pain

signs of a failed root canalIf your treated tooth continues to be the source of pain, it may be indicating that you may require another root canal procedure.

Typically you should experience some pain following the procedure to remove tooth decay. Should that pain be prolonged, for more than a week, you may have a failed root canal.

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Tooth Sensitivity

Another sign of bacteria remaining after the completed root canal procedure is sensitivity when chewing food. Generally speaking, you should just eat soft food for the first few days after your procedure.

If hot or cold food causes you difficulty, you may need to treat teeth with another root canal.

No Temperature Feeling

Another of the signs of a failed root canal is when teeth do not respond to heat or cold. There may be a short period of time when this happens, but if it lasts longer than a few days, it is a serious problem.

Consuming really hot or cold foods may damage the tooth but after a few days you should regain temperature feeling. If you do not, you should contact your dentist right away.

Swelling/Staining of Gums

This is one of the failed root canal symptoms that points to an obvious issue. When gums become irritated following a procedure and do not heal properly, you know that the root canal has failed. It may be related to the gutta-percha used in the procedure or something more. When your gums swell they cause you difficulty in eating, speaking and smiling.

Pain in The Tooth

While it is not uncommon to feel some amount of pain following a root canal treatment, if the pain subsides and then returns after a short period of time, it is a sign of bacteria growth that has created an infection.

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This kind of pain in the tooth will feel like no other as it will originate from the inside, interior of the tooth.


Any kind of facial swelling that occurs following a root canal treatment indicates the presence of an infection. If this happens, contacting your dentist right away is recommended. Facial swelling must be treated as soon as possible as it can impact eating, speaking and other facial expressions.

What If Root Canal Treatment Was Left Incomplete?

When a root canal is left unfinished a number of issues can develop. The tooth will most likely cause you pain. The tooth may also crack which could result in the need for a dental crown. The fracture may cause swelling in the gum which would definitely point to a failed root canal.

Treating A Failed Root Canal

If you are still in pain following the use of rights reserved, filling material as part of your root canal procedure, an x-ray will be taken. It is through this that a failed root canal can be confirmed. It may result in tooth extraction in order to save your tooth.

Regardless of the treatment, the best way to see what is happening inside that tooth is with an x-ray.

If X-Ray will confirm a failed root canal, then the most effective way to re-do a root canal treatment is through a hole that is made through the crown of the tooth.
failed root canal

There are also times when tooth extraction after root canal failed is the best and most logical course of action. If the infection around the tooth root has not originated from inside the tooth, a surgical procedure will be performed.

A root canal retreatment is likely the best thing to do to remedy a failed root canal. The procedure is the same as the first root canal with the addition of a couple of extra stages.

A root canal retreatment is likely the best thing to do to remedy a failed root canal

The retreatment will require two dental visits:

  • The first one is to remove all of the root canal filling material (gutta-percha).
    This is replaced with calcium hydroxide which is a paste with antibacterial properties.A temporary filling material is then used to close the tooth. With the antibacterial material ‘trapped’ inside the tooth for a period of time, it reduces the bacterial growth inside the tooth.
  • The second visit is when the calcium hydroxide paste is removed.
    The canals receive another cleaning and shaping. Following this, new root canal filling is installed.A temporary filling closes the opening to the tooth and completes the retreatment procedure.

Once the tooth has completely restored, another visit to your dentist will be required.

This is so that the temporary filling can be removed. However, there is also the possibility that the temporary filling has failed and fallen out. Because the tooth is susceptible to infection resulting from the loss of the temporary filling, it is recommended that you see your dentist immediately in order to have the tooth returned to complete functionality without issue.


A root canal treatment, although with a high success rate, can still fail. The causes are many but basically result from the growth of bacteria that develops into an infection. The infection can invade the weakened tooth and can create serious oral health issues.

However, root canal treatment is a common procedure used in treating teeth that are infected from the inside of the tooth. When a root canal fails, and they do fail on occasion, infection is still likely and can once again develop into a serious dental issue.

The most common way to retreat a root canal problem is to either repeat the original treatment or extract the tooth that has been damaged enough to make a successful retreatment unlikely.

Still, retreatment of a failed root canal is common and comes with some risk associated with it but a high rate of success as well.

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