A root canal, or endodontic treatment, is a standard procedure designed to save a severely infected or damaged tooth. The goal is to remove the infected pulp tissue, clean the internal canal system, and seal the space to prevent bacterial intrusion. While the procedure is highly successful, with success rates often exceeding 90%, a treated tooth remains susceptible to new issues.
Understanding Root Canal Failure
Yes, an old root canal can get infected. When a previously treated tooth develops a persistent or recurring infection, it is clinically termed “failure,” specifically post-treatment periapical disease. This failure is defined by a renewed infection, usually at the root tip, which is often only visible on a dental X-ray. Failure occurs when microorganisms either survive the initial cleaning or find a way to re-enter the sealed canal system later on. This bacterial presence causes inflammation in the surrounding bone and tissue, requiring further professional intervention.
Common Reasons for Root Canal Re-infection
The most frequent mechanism for re-infection is known as coronal leakage, which happens when the final restoration breaks down over time. Oral bacteria can seep past a faulty filling or a cracked crown margin and contaminate the root canal filling material. This leakage provides a pathway for bacteria to travel down the length of the tooth into the previously cleaned root tip area. The delayed placement of a permanent crown after the root canal procedure can also increase the risk of this type of contamination.
Another common cause relates to the complex and intricate anatomy of the tooth’s interior. Teeth are not simple tubes, but possess a system of tiny accessory canals, lateral canals, and isthmuses that connect the main canals. If these microscopic branches were not thoroughly cleaned and disinfected during the first procedure, bacteria can survive and multiply, leading to a persistent low-grade infection. This situation is particularly common in molars, which often have an unexpected fourth canal that may have been missed during the original treatment.
A significant structural problem that leads to failure is the development of a tooth fracture or crack. Endodontically treated teeth can be more brittle due to the loss of internal structure, making them susceptible to hairline cracks, especially under heavy chewing forces. A vertical root fracture, which runs along the length of the root, creates a direct and irreparable pathway for bacteria to colonize the root canal system and the surrounding bone. Even a tiny crack or a new deep cavity forming around the crown margin can allow bacteria to bypass the seal and re-contaminate the entire tooth structure.
Identifying the Symptoms of a Failed Root Canal
The signs of a recurrent infection can appear months or even years after the original root canal procedure was completed. Patients often report the return of pain, especially sensitivity or tenderness when they bite down or apply pressure to the treated tooth. This recurring pain indicates inflammation in the periodontal ligament surrounding the tooth root, which is reacting to the bacterial byproducts.
Localized swelling in the gum tissue near the affected tooth signals an active infection. In some cases, the body attempts to drain the infection, resulting in a small, raised, pimple-like lesion on the gum called a sinus tract or fistula. This lesion may periodically release pus, but the opening typically closes and reopens without fully resolving the underlying infection.
The tooth itself may exhibit a noticeable darkening or grayish discoloration, which is a sign of internal staining from byproducts of the infection. However, failure can sometimes be completely asymptomatic, meaning the patient feels no pain or swelling at all. In these silent cases, the infection is often discovered incidentally during a routine dental check-up when a dentist notices a periapical radiolucency, or dark spot, on an X-ray.
Treatment Options for an Infected Root Canal
When a failed root canal is diagnosed, the first and most common course of action is non-surgical retreatment. This procedure involves carefully reopening the tooth, removing the old root canal filling material, and meticulously re-cleaning the entire canal system. The endodontist aims to locate and address any previously missed anatomy or persistent bacteria before re-sealing the canals and placing a new, definitive coronal restoration.
If the non-surgical approach is not possible due to a blocked canal, a complex restoration like a post, or if the retreatment fails to resolve the infection, a minor surgical procedure called an apicoectomy may be recommended. During an apicoectomy, the endodontist accesses the infection through the gum tissue. They remove the very tip (apex) of the tooth root along with the surrounding infected tissue, and place a small seal directly into the end of the root.
Extraction, or the removal of the tooth, is reserved as the final option when both non-surgical retreatment and apicoectomy procedures are unable to save the tooth. This choice is typically made when the tooth has sustained a non-repairable vertical root fracture or when the amount of remaining tooth structure is insufficient to support a successful restoration. If extraction is necessary, the patient will then explore options for tooth replacement, such as a dental implant or a bridge.