A root canal, or endodontic treatment, is a common procedure designed to save a tooth that has become infected or severely damaged. The process involves removing the infected pulp tissue from the tooth’s interior, disinfecting the canal system, and sealing it to prevent future microbial invasion. This treatment boasts a high success rate, with outcomes generally ranging from 86% to over 95% for retaining the tooth long-term. Despite this strong prognosis, a small percentage of treated teeth may not heal properly or may develop new issues years later, confirming the possibility of a root canal “going bad.”
Causes of Root Canal Failure
One of the most frequent causes of failure is the breakdown of the seal, known as coronal leakage. This occurs when the final restoration, such as a crown or filling, is inadequate, allowing bacteria from the mouth to seep back into the root canal system. Leakage may also happen if the permanent crown placement is significantly delayed after the initial procedure, leaving the temporary filling vulnerable to compromise. If bacteria reinvade the tooth’s interior, a new infection can begin at the root tip.
Failure often relates to the complex anatomy within the tooth. Some teeth have accessory canals, or extremely small, curved channels that were not properly located and cleaned during the initial procedure. Residual bacteria in these missed areas can multiply, leading to persistent infection and inflammation around the root. Incomplete cleaning and sealing of the main canals, due to blockage or underfilling, also allows surviving microorganisms to flourish.
Structural complications can also compromise the tooth. A fine crack or fracture in the tooth root, which can happen years later, creates a pathway for oral bacteria to enter the surrounding jawbone. The fracture compromises the tooth’s integrity, preventing a proper seal and leading to persistent infection. Even if the initial endodontic treatment was perfect, a compromised tooth structure can lead to failure.
Recognizing the Signs of a Problem
The most recognizable sign of a failed root canal is the return of persistent pain in the treated tooth. This discomfort may range from a dull ache to a sharp pain, especially when chewing or biting down. Unlike the initial post-procedure soreness that fades, this pain indicates an ongoing inflammatory or infectious process within the bone surrounding the root.
Swelling and tenderness around the affected tooth are common physical indicators of an issue. Localized puffiness in the gums near the root is often accompanied by sensitivity to touch. A small, pimple-like bump on the gum, termed a fistula or sinus tract, is a strong sign of failure. This bump is a channel through which pus from the underlying infection, or abscess, drains into the mouth.
Other symptoms that suggest a problem include a change in the tooth’s appearance or feeling of looseness. The treated tooth may look darker or discolored compared to adjacent teeth, indicating internal damage or residual infection. Mobility or a loose tooth sensation, typically caused by bone loss from chronic infection, signals a need for re-evaluation.
Options After a Failed Procedure
If root canal failure is confirmed, the first course of action is non-surgical retreatment. This involves reopening the tooth, removing the previous filling material, and using advanced techniques to clean, disinfect, and reseal the canal system. Retreatment is often highly successful, especially if the original cause was a missed canal or coronal leakage, and it is the best method for preserving the natural tooth structure.
If retreatment is not feasible due to complex obstructions, such as a separated instrument or calcified canals, an apicoectomy is the next solution. This minor surgical procedure involves the endodontist accessing the root tip through the gum tissue. The root tip and infected tissue are removed, and a small filling is placed to seal the end of the root directly, bypassing the need to navigate the canal.
Extraction is the final option when retreatment and apicoectomy have failed or if the tooth is structurally unsalvageable (e.g., severe vertical root fracture). Replacement is necessary to maintain proper bite function and prevent shifting of adjacent teeth. Common replacement solutions include a dental implant, which functions as a standalone artificial root, or a fixed dental bridge.