A tooth can undergo more than one root canal. A second procedure on the same tooth is known as non-surgical retreatment, which becomes necessary when a previously treated tooth fails to heal or develops a new infection. This failure means symptoms like pain, swelling, or signs of infection visible on an X-ray have returned or persisted after the initial therapy. The goal of retreatment is to eliminate bacteria from the internal canal system and save the natural tooth structure, offering a common and highly successful option for preserving teeth.
Why a Root Canal Might Fail
A root canal treatment may fail due to several reasons, often related to the complex anatomy of the tooth. One cause is the presence of undetected or accessory root canals that were not fully cleaned during the first procedure. Molars often have narrow or curved canals that are difficult to locate and disinfect completely. If bacteria remain in a missed channel, they can multiply and lead to a persistent infection in the surrounding bone.
Coronal leakage is another factor, occurring when the final restoration, such as a filling or crown, breaks down or cracks. This breach allows saliva and bacteria to seep back into the cleaned root canal system, causing re-infection. Delaying the placement of the permanent crown after the initial root canal can also expose the treated tooth to contamination. Finally, new trauma or extensive decay can compromise the original seal, leading to bacterial invasion.
The Non-Surgical Retreatment Process
Non-surgical retreatment is often performed by an endodontist, a specialist in root canal therapy, due to its complexity. The procedure begins by gaining access to the inner tooth, carefully removing the existing crown and filling material. The most challenging step involves dissolving and removing the old gutta-percha, the material used to fill the canals during the first treatment.
Specialized rotary instruments and chemical solvents are used to remove the prior filling material from the curved and narrow canals. The clinician uses high-magnification tools, like a dental operating microscope, to search for and treat any missed anatomy, such as tiny lateral canals. The canals are then thoroughly re-cleaned, shaped, and flushed with disinfecting solutions to eliminate bacterial colonies. Once disinfected, the canals are filled with fresh gutta-percha and a sealer to create a dense seal. The access opening is then closed with a temporary filling, preparing the tooth for a new permanent restoration.
When Surgical Intervention Is Necessary
If non-surgical retreatment is not feasible or fails to clear the infection, a surgical procedure known as an apicoectomy is considered. This procedure approaches the infection from the outside of the tooth, through the gum tissue and jawbone. Apicoectomy is recommended when the root canal is blocked by an obstruction, such as a metal post or a broken instrument, that cannot be safely removed from the top of the tooth.
During the procedure, the endodontist makes a small incision in the gum near the affected tooth to access the underlying bone and the root tip (apex). The infected tissue and the end of the root are surgically removed. A biocompatible filling material, such as Mineral Trioxide Aggregate (MTA), is then placed to seal the root end. This seal prevents bacteria from escaping the canal system and allows the surrounding bone to heal naturally.
The Final Consideration: Extraction
If both non-surgical retreatment and surgical apicoectomy fail, or if the tooth is too compromised to save, extraction becomes the final consideration. This option is reserved for cases involving a severe vertical root fracture, which is an irreparable crack running down the length of the root. Extensive bone loss due to advanced periodontal disease can also make the tooth unsalvageable. Although the goal is always to preserve the natural tooth, extraction may be necessary to eliminate chronic infection and protect oral health. Following extraction, the missing tooth must be replaced, usually with a dental implant or a fixed bridge, to maintain proper bite function and prevent adjacent teeth from shifting.