Updated on March 8, 2024
6 min read

Old Root Canal Infection Symptoms

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What are Root Canal Infections?

Root canal therapy has a high success rate at approximately 95%, and many treated teeth last a lifetime1. However, there’s a slight chance the treated tooth may become re-infected.

3d render of jaw with tooth cavity and cyst or dental pulp

Root canal treatment involves removing the infected or damaged pulp from the inner chamber of a tooth. Even though re-infection of the tooth is rare, it can happen.

Knowing the causes and symptoms of a root canal infection can help ensure you receive timely treatment.

Root Canal Infection Symptoms

The most common root canal infection symptoms include:

Tooth Pain

Tooth pain can manifest in many ways, including:

  • Sharp pain when biting or putting your teeth together 
  • Intermittent pain
  • Pulsing pain 
  • 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 severe 
  • A pimple or boil appears near the tooth tip 
  • The tooth feels taller than the surrounding teeth.

Bad Breath, Pus, or Abscess

Infections can cause bad breath. They may also produce pus that creates a bad taste and smell in your mouth. A dental abscess is a small pus-filled pocket. It 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. Localized discoloration may be a sign of an infection that needs to be treated as soon as possible. 

What Causes a Root Canal Infection?

Common reasons for complications include:

  • 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 or another root canal. However, endodontic surgery may be necessary.

Apicoectomy is the most common endodontic treatment for a failed root canal. During this procedure, the soft tissue around the tooth root is opened, the infected tissue is extracted, and sometimes the tip of the tooth’s root is removed.

Can a Root Canal Infection Spread?

Yes. If not treated promptly, a root canal infection can spread to other parts of the body, including:

  • Other teeth
  • Gums and oral tissues
  • Cheeks and face

A root canal infection won’t go away on its own. Seeking treatment at the earliest signs of a root canal infection can help prevent the infection from spreading.

When to See a Dentist

Call your dentist to schedule another visit if you experience any of the above signs and symptoms of a root canal infection.

Treatment for Root Canal Infections

Here are some common treatments for root canal infections: 

Endodontic Retreatment

Typically, endodontic retreatment can save a root canal. This procedure is very similar to root canal therapy.

  1. The endodontist reopens the tooth that’s been treated
  2. They remove the root canal filling material to gain access to the root canal
  3. The endodontist cleans the canal with instruments and medicaments 
  4. They carefully examine the inside of the tooth with light and magnification tools, looking for unusual anatomy like canals that might have been missed during the first root canal 
  5. They fill and seal the canal and protect the tooth with a temporary crown

After endodontic retreatment, you must return to your dentist for a permanent crown or other restoration.

Endodontic Surgery

Endodontic surgery may be recommended as an alternative or in conjunction with retreatment. You may need surgery if your root canals are blocked or narrow.

Many surgical procedures can save an infected tooth. The most common is an apicoectomy, also known as a root-end resection. During this procedure:

  1. The endodontist makes an incision in the gum near the tooth, exposing the underlying bone and infected tissue
  2. They remove any inflamed or infected tissue
  3. They remove the end of the tooth’s root
  4. They may seal the end of the root canal with a small filling before closing the incision with a few stitches

Tooth Extraction

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

  1. The dentist uses specialized instruments to loosen the tooth and remove it from its socket
  2. In some cases, they may need to make incisions in your gums to access the tooth
  3. After the tooth is removed, they clean and disinfect the socket
  4. If needed, they place a dental bone graft in your jaw to prevent bone loss
  5. They may use stitches to close the soft tissue

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

How To Prevent a Root Canal Infection

There are many steps you can take to help reduce your risk of reinfection after root canal treatment:

  1. Brush your teeth at least twice daily
  2. Floss as advised by your dental hygienist
  3. Rinse with a gentle, antiseptic mouthwash for at least the first few days after the procedure
  4. Take an over-the-counter (OTC) pain reliever like ibuprofen for soreness
  5. Return to your dentist for a permanent crown or restoration as soon as possible
  6. Call your dentist right away if you experience any signs of infection

Seeing your dentist twice a year for routine exams and cleanings can help catch infections early and maintain healthy teeth.

Root Canal Treatment

Root canal therapy is a standard endodontic procedure that removes the infected or damaged pulp from a tooth. 

endodontic root canal procedure steps

Your teeth are made up of layers. Dentin, the soft layer below your tooth enamel, contains the pulp chamber. The pulp is a gel-like material inside the tooth. It stores the blood vessels, connective tissues, and tooth nerves and provides sensation.  

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

What to Expect During a Root Canal

A root canal procedure can generally be performed in one to four appointments. 

During the first appointment, the doctor will:

  1. Take an X-ray 
  2. Numb the tooth 
  3. Remove the pulp tissue  
  4. Place a temporary filling material called calcium hydroxide into the root of the tooth

The dentist cleans and shapes the treated tooth’s root canals at the second appointment, placing the permanent filling material called gutta percha into the tooth’s root.

If necessary, the third and fourth appointments are when a crown, or other restorative dental procedure, is completed to restore the tooth to full function.


  • Root canal therapy is a common dental procedure that involves removing damaged or infected tissue from the inner chamber of a tooth.
  • Though root canal treatment is safe and effective most of the time, re-infection can occur.
  • Root canal infections are treatable with endodontic retreatment, surgery, or extraction.
  • To prevent a root canal infection, clean your teeth as advised by your dentist, and return for a permanent restoration promptly.

Last updated on March 8, 2024
13 Sources Cited
Last updated on March 8, 2024
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).
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  2. Estrela, Carlos et al. Characterization of Successful Root Canal Treatment. Braz. Dent. J. [online]. 2014.
  3. American Association of Endodontists (AAE). Root Canal Treatment. 2 Sept. 2020.
  4. Siqueira José F., et al. Patterns of microbial colonization in primary root canal infections, Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, Volume 93, Issue 2, 2002, Pages 174-178.
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  6. Toru Matsumoto et al., Factors affecting successful prognosis of root canal treatment, Journal of Endodontics, Volume 13, Issue 5, 1987, Pages 239-242. 
  7. 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.  
  8. Siqueira, J. F. “Aetiology of Root Canal Treatment Failure: Why Well-Treated Teeth Can Fail.” Wiley Online Library, International Endodontic Journal, 7 July 2008. 
  9. FJ;, Smith CS;Setchell DJ;Harty. Factors Influencing the Success of Conventional Root Canal Therapy–a Five-Year Retrospective Study. Nov. 1993. 
  10. 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. 
  11. Wu, M. K., et al. Consequences of and Strategies to Deal with Residual Post-Treatment Root Canal Infection. 13 Mar. 2006.
  12. Sundqvist, G. Associations between Microbial Species in Dental Root Canal Infections. Oct. 1992.
  13. American Association of Endodontists (AAE). Endodontic Retreatment Explained. n.d.
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