A root canal procedure saves a severely infected or decayed tooth by removing the inflamed or infected soft tissue, known as the pulp, from the tooth’s interior. The pulp, which contains nerves and blood vessels, is removed, and the inner chamber and root canals are thoroughly cleaned, disinfected, and sealed. The intent is to eliminate bacteria and prevent reinfection, allowing the tooth to remain functional. While the procedure is highly successful (85% to 97% success rates), a treated tooth can definitively become infected again.
Why Root Canals Sometimes Fail
The failure of a root canal, which allows bacteria to return and cause a new infection, is often tied to the microscopic complexity of the tooth’s internal anatomy. The intricate network of tiny root canals can include hidden branches or accessory canals that are too narrow or curved to be completely disinfected during the initial treatment. If these areas harbor residual bacteria, the infection can eventually flare up again, even years later.
Another cause of failure relates to the final restoration placed on the tooth after the procedure is complete. If a permanent crown or filling is delayed, breaks, becomes loose, or develops a marginal leak, bacteria can infiltrate the sealed root canal system. This allows oral bacteria to bypass the seal and recontaminate the disinfected interior of the tooth.
A common reason for reinfection is new decay that forms around the edges of the permanent restoration, compromising the seal and creating an entry point for microbes. A vertical root fracture, a crack that starts in the root and extends upward, can also allow bacteria to enter the inner tooth structure. Such a fracture is difficult to detect and seal, leading to persistent infection that cannot be resolved with non-surgical treatment.
Recognizing Symptoms of Post-Procedure Infection
Recognizing the signs of a failed root canal is important for timely intervention, as the symptoms often resemble those of the initial infection. Persistent or recurring pain is a primary indicator, especially if the discomfort returns long after the initial post-procedure soreness has faded. This pain may be noticeable when chewing or applying pressure to the tooth.
Swelling or tenderness in the gum tissue near the treated tooth is another common sign of an underlying infection. This inflammation can progress to the formation of a small, pimple-like bump on the gum, known as a fistula or sinus tract. This bump allows pus and infected fluid to drain from the abscessed area at the root tip, often resulting in a chronic bad taste or foul odor.
The infected tooth may also show noticeable discoloration, often appearing darker or greyer than the surrounding teeth. This color change indicates internal issues caused by bacterial activity or breakdown products within the tooth structure. Lingering sensitivity to hot or cold temperatures, which should have resolved after the initial root canal, is also a warning sign of reinfection.
Treating a Failed Root Canal
When a root canal fails, the initial treatment option is Root Canal Retreatment, a non-surgical procedure similar to the original. The endodontist re-enters the tooth, removes the old filling material, and uses specialized tools to thoroughly clean and disinfect the entire root canal system again. This process aims to eliminate any bacteria that were missed or that re-entered the tooth before sealing the canals with fresh material.
If retreatment is not possible due to structural issues or fails to resolve the infection, the next option is an Apicoectomy. This minor surgical procedure involves the endodontist accessing the infection through the gum tissue, rather than the top of the tooth. They remove the tip of the tooth’s root, known as the apex, along with any surrounding infected tissue, before placing a small seal over the root end.
The final option is Extraction, reserved for cases where the tooth is severely fractured, has insufficient supporting bone, or has failed to heal after retreatment and apicoectomy. If the tooth cannot be salvaged and the infection persists, its removal is necessary to prevent the spread of infection to the jawbone and surrounding tissues. Following extraction, the patient needs to consider a tooth replacement option, such as a dental implant or bridge.