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Old Root Canal Infection Symptoms

Michael Bayba Headshot
Written by
Michael Bayba
Medically Reviewed by 
Dr. Erica Anand
11 Sources Cited

What Is Root Canal Treatment?

Root canal therapy is a standard endodontic procedure that repairs decayed or damaged teeth.

It is necessary when the pulp of a tooth becomes infected or damaged. 

endodontic root canal procedure steps

Dentin, the soft layer below your tooth enamel, contains the pulp chamber. The pulp is a gel-like material inside the tooth that stores the blood vessels, connective tissues, and tooth nerves. The nerve is contained within the pulp chamber and root of the tooth. Root canals contain pulp and stretch from the tip of the root into the pulp chamber.

The tooth’s nerve is not necessary for a tooth to function properly. Its only function is to provide sensation.

If the pulp of the tooth is damaged, it may cause:

A general dentist or an endodontist may perform root canal therapy (often referred to as a root canal). An endodontist is a dentist that has received an additional two to three years of education on diagnosing and treating tooth infections.

The root canal procedure can generally be performed in two or three appointments. 

During the first appointment, the doctor will take an X-ray, numb the tooth, extract the pulp, and place a temporary filling material called gutta-percha into the root of the tooth.

At the second appointment, the dentist cleans, shapes, and reseals the treated tooth’s root canals. If necessary, the third appointment is when a crown, or other restorative dental procedure, is placed to restore the tooth to full functionality.

What Causes a Root Canal to Fail?

Root canal therapy has a high success rate at approximately 95%, and many treated teeth last a lifetime. However, there is always a risk of infection after a root canal procedure.

Common reasons for complications include:

  • An excessive number of root canals in the tooth (if one is not cleaned the infection can spread again)
  • An undetected fracture or crack in the affected tooth
  • An insufficient dental restoration that allows bacteria to penetrate the tooth
  • Breakdown of the inner root canal filling material over time
  • New cavities that develop around the affected tooth

Sometimes the infected tooth can be saved by retreatment. However, endodontic surgery may be necessary.

The most common endodontic treatment for a failed root canal is an apicoectomy, where the gum’s soft tissue is opened, the infected tissue is extracted, and sometimes the tip of the tooth’s root is removed.

Can an Old Root Canal Cause an Infection?

Yes, it is possible for the filling inside of a root canal tooth to decompose over time, leading to infection.

An inadequate filling or dental restoration can also cause bacteria to enter the tooth and cause an infection. In addition, if the patient doesn’t maintain their oral health by brushing their teeth, flossing, and using mouthwash daily, additional tooth decay may necessitate retreatment. 

Root Canal Infection Symptoms

The most common root canal infection symptoms include:

Tooth Pain

Tooth pain can manifest in sensitivity to hot and cold, sharp pain when biting or putting your teeth together, intermittent pain, pulsing pain, or a constant, lingering toothache.

Gum Sensitivity and Swelling

Gum swelling and pain are other common symptoms of infected root canals.

The tooth is likely infected if the swelling lasts for an extended period, the swelling is very pronounced, there is a pimple or boil that appears near the tooth tip, or the tooth feels taller than the surrounding teeth.

Bad Breath, Pus, or Abscess

Infections can smell foul. They may also produce pus that creates a bad taste and smell in your mouth. A dental abscess is a small pus-filled pocket that looks like a small bump that is swollen and sensitive.

Tooth Discoloration

Limited blood flow to a tooth can cause it to have a gray, blue, or dark yellow tone to it. This is a sign of a bad infection that needs to be treated as soon as possible. 

Root Canal Infection Treatment Options

Endodontic Retreatment

Typically, endodontic retreatment can save a root canal.

This procedure is very similar to root canal therapy.

The dentist removes the original filling material to reclean and reseal the canals. They will then place a temporary filling, and you will come back for a permanent restoration at a different appointment.

Endodontic Surgery

Endodontic surgery may be recommended as an alternative to, or in conjunction with retreatment.

During endodontic surgery, the gum tissue is opened, exposing the tooth root. The infected tissue is then extracted, and if necessary, the tip of the tooth root is removed as well.

Tooth Extraction

The only other alternative to retreatment and surgery is to extract the infected tooth.

The tooth is then replaced with a dental implant, bridge, or partial denture in order to restore normal function and keep the surrounding teeth in place. 

Last updated on April 22, 2022
11 Sources Cited
Last updated on April 22, 2022
All NewMouth content is medically reviewed and fact-checked by a licensed dentist or orthodontist to ensure the information is factual, current, and relevant.

We have strict sourcing guidelines and only cite from current scientific research, such as scholarly articles, dentistry textbooks, government agencies, and medical journals. This also includes information provided by the American Dental Association (ADA), the American Association of Orthodontics (AAO), and the American Academy of Pediatrics (AAP).
  1. Estrela, Carlos et al. Characterization of Successful Root Canal Treatment. Braz. Dent. J. [online]. 2014, vol.25.
  2. American Association of Endodontists (AAE). Root Canal Treatment. 2 Sept. 2020
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  6. Ng, Y.‐L., et al. “Outcome of Primary Root Canal Treatment: Systematic Review of the Literature – Part 2. Influence of Clinical Factors.” Wiley Online Library, International Endodontic Journal, 11 Oct. 2007.  
  7. Siqueira, J. F. “Aetiology of Root Canal Treatment Failure: Why Well‐Treated Teeth Can Fail.” Wiley Online Library, International Endodontic Journal, 7 July 2008
  8. FJ;, Smith CS;Setchell DJ;Harty. Factors Influencing the Success of Conventional Root Canal Therapy--a Five-Year Retrospective Study. Nov. 1993
  9. Hülsmann, M, and I Schinkel. Influence of Several Factors on the Success or Failure of Removal of Fractured Instruments from the Root Canal. Dec. 1999
  10. Wu, M.‐K., et al. Consequences of and Strategies to Deal with Residual Post‐Treatment Root Canal Infection. 13 Mar. 2006
  11. Sundqvist, G. Associations between Microbial Species in Dental Root Canal Infections. Oct. 1992
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