Re-infection After Root Canal Treatment: Signs, What to do

A dentist performs root canal treatment to an infected tooth. He or she does it by removing the tooth’s pulp, cleaning the root canal and filling up the empty canal (click here to read more about root canal). If done properly, the bacteria will not be able to infect the tooth anymore. However, there are chances that the root canal treated tooth could be infected again. When it happens it is called re-infection of the root canal. Let us explore why and how the dentist solves it.

How can a root canal treated tooth get reinfected?

Technically, a pulp-less root canal cannot be infected anymore because the infection can only happen on living tissue.

Having said that, a root canal treated tooth is still supported by surrounding living tissue, eg. gum and jawbone. An infection can still happen in two scenarios:

1. If new decay forms around the filling of the root canal treated tooth. When this happens, the filling’s defect can allow the bacteria to enter the poorly filled root canal and reach to the tip of the root. From there, the bacteria can start infecting the bone tissue surrounding the root tip (Figure 1).
   Examples are bacteria remnants in the canal or new cavity forms under the tooth filling. You can click here to read more about Signs of Decay Under Fillings.
2. If the bacteria have already existed in the bone tissue before the root canal treatment is done. In this case, root canal treatment will not be able to remove those bacteria as they reside outside the root canal (Figure 2).

To suggest an analogy, a decorative plant will not be damaged by bugs. However, the bugs could still invade the soil supporting the plant, giving trouble to you.

What happens if you get a re-infection after a root canal?

Pain or discomfort after a root canal procedure is common. However, this kind of pain is mild and will just disappear by itself over a week or slightly longer.

If the pain persists, or the pain appears long after the root canal is done, it may mean that the tooth is re-infected. You can confirm this by gently tapping your tooth with fingernails (by gently flicking the finger). If you feel pain upon tapping the tooth, the bacteria have likely invaded the root treated tooth and start infecting the part surround the tooth root tip.

Symptoms of re-infection of root canal

If you feel only slight pain, it could mean that the infection is only at the initial stage. This usually is not dangerous and is not an emergency.

However, if it is left untreated, the infection can progress to involve a bigger area. Sometimes the bacteria can find their way through the bone and spread to the areas surrounding the jawbone. This can lead to swelling of the face or the jaw, which is called “space infection”. The infection progresses further when the bacteria and enter the bloodstream, causing blood infection which can be a life-threatening situation.

When there is a re-infection of the root canal, it is a root canal failure. Some of the signs and symptoms of root canal failure are:

• Persistent pain for weeks or months after root canal treatment
• Sudden occurrence of pain long after root canal treatment
• Pain on touching or tapping the tooth
• Swelling of gum around the tooth involved
• Gum boil near the tooth involved
• Yellowish pus or bleeding near the tooth involved
• Mobile or shaky tooth

You should go back to your dentist if you are feeling the above symptoms.

Treatment of root canal re-infection

Your dentist will investigate more to confirm the source of the pain. An X-ray will be the most useful tool here. It can be a small X-ray film placed in the mouth or a big X-ray machine (CBCT – Cone Beam Computed Tomography) to see more detail in a 3-dimensional view. 

Besides, the dentist will likely find out the reason for the re-infection after the root canal. The reasons can be grouped into three categories:

1. Bacteria remnants inside the poorly filled root canal.
2. Presence of infection or cyst outside the reach of root canal treatment.
3. A fractured tooth in which the fracture line becomes a pathway for bacteria (Figure 3).

1. Root canal re-treatment – for poorly filled root canal

A poorly filled root canal can be re-treated. This means to drill a hole into the tooth again and remove the filling in the root canal. Then, the dentist cleans the canal thoroughly and fill it up again. If the bone tissue surrounding the tooth root starts healing, then this approach is sufficient.

2. Surgery – for infection beyond root tip

Sometimes the infection may not go away after trying re-treatment because it involves deeper bone tissue. It may mean that the infection is out of reach of root canal treatment. In this case, surgery is needed to treat the infection.

The surgery will involve numbing the area and making a gum into the gum and the bone just enough to gain entry to the infection area. The dental surgeon then cleans that area to remove the infection or cyst if present. After that, the surgeon closes back the wound. 

3. Extraction – for tooth fracture

If a tooth fracture involving root or a split in the center of the tooth is confirmed on X-ray, it is unlikely that the tooth can be saved.

Summary

In short, an infection can happen to a root canal that has been filled. The reasons could be the persistence of bacteria inside the canal or infection in the bone tissue surrounding the root tip.

To remove the infection inside the canal, dentists generally attempt retreatment without involving surgery. If the infection is in the bone tissue surrounding the root tip, it may need a small surgery to remove the infection.

Reference

1. Anuradha B, Sharumathi R, Venkatesh A, Niveditha S. Endodontic treatment Failures and its Management―A Review. Indian Journal of Public Health Research & Development. 2019;10(11):3049.
2. Tabassum S, Khan F. Failure of endodontic treatment: The usual suspects. European Journal of Dentistry. 2016;10(01):144-147.
3. Endodontic Retreatment Explained | American Association of Endodontists [Internet]. American Association of Endodontists. 2020 [cited 4 October 2020].
   Available from: https://www.aae.org/patients/root-canal-treatment/endodontic-treatment-options/endodontic-retreatment/endodontic-retreatment-explained/