Teeth may require further management following root canal treatment because of persisting or new apical pathosis. Management must be based on the diagnosis of the presenting condition and the history of the previous treatment, particularly in relation to when it was completed. Most root-filled teeth with periapical pathosis should be re-treated in the first instance via a conventional orthograde approach since most disease is related to an infected root canal system. However, this approach to treatment should only be followed if the tooth is suitable for further restoration and when the restoration has a good long-term prognosis. Assessment of whether a tooth is suitable for treatment may not be possible until after restorations, caries, and cracks have been removed so that the remaining tooth structure can be visualized and assessed. Periapical surgery should be reserved for teeth with persistent symptoms and/or apical radiolucency following root canal re-treatment and where the differential diagnosis suggests an ongoing periapical condition such as a true cyst, extra-radicular infection, or foreign body reaction which cannot be addressed via an orthograde approach. If a tooth has to be extracted, it can be replaced with one of several forms of prostheses; implant-supported prostheses are gaining popularity and have a proven track record, especially for single tooth replacements. The use of implants should be restricted to cases where teeth are already missing or where a tooth cannot be retained because it is not suitable for further restoration due to insufficient tooth structure.

Safe, successful and effective removal of root filling materials is an integral component of non-surgical root canal re-treatment. Access to the root canal system must be achieved in order to negotiate to the canal terminus so that deficiencies in the original treatment can be rectified. Since a range of materials have been advocated for filling root canals, different techniques are required for their removal. The management of commonly encountered root filling materials during non-surgical re-treatment, including the clinical procedures necessary for removal and the associated risks, are reviewed. As gutta-percha is the most widely used and accepted root filling material, there is a greater emphasis on its removal in this review.

In this narrative review, the differences between primary root canal treatments and re-treatments are explored in view of optimal disinfection of the root canal system. A critical appraisal of the literature raises doubt as to whether the microbiota found in re-treatment cases per se is more resistant to antiseptics than the counterpart found in primary infections. In reality, primary, refractory, and persisting endodontic infections are all biofilm-related; their microbial composition is dictated by local ecological factors rather than treatment history. Furthermore, their resistance to antimicrobials is most likely similar. The true difficulty in disinfecting root canal systems during re-treatment cases is to achieve access to the infected areas. Iatrogenic alterations in canal anatomy and the presence of root filling material hamper the diffusion of disinfectants to these target areas. Consequently, cleaning the canal systems of foreign material and creating a canal shape that can properly be disinfected should be the initial aims. Ways of achieving these goals are discussed. Subsequently, the disinfection regimen can be similar to that in primary root canal infections. However, time is a crucial factor in re-treatments, and thus a multiple-visit approach is preferable in more complex cases in order to ensure more complete disinfection has been achieved.

Re-treatment of primary root canal treatment associated with post-treatment disease has become an important component of daily endodontic practice. Basically, the management of cases requiring re-treatment should comply with the general rules of primary root canal treatment namely accurate diagnosis, antiseptic treatment consisting of cleaning and shaping the root canals, followed by effective disinfection, canal filling, and a coronal restoration that prevents re-infection. Nevertheless, re-treatment represents a distinct treatment modality of its own, which in several respects differs from primary treatment of teeth with vital or necrotic pulps. The aim of this review is to present current knowledge on root canal preparation and filling during root canal re-treatment.

There have been many recent advances in the methods available for restoring root-filled teeth that can equally be applied to re-treatment cases. Most of these advances are related to adhesive techniques, composite resin materials, non-metallic posts, and indirect ceramic materials. These new techniques and materials have enhanced the options available when restoring root-filled teeth. However, the preservation of sound tooth structure is clearly the most significant factor influencing the survival of teeth following root canal re-treatment. Although contemporary adhesive techniques will facilitate the preservation of valuable dentin in the re-treated tooth, the degree of remaining sound tooth structure will ultimately be dictated by the extent of the existing restoration, carious and non-carious tooth tissue loss, and iatrogenic tooth tissue loss caused during the previous endodontic and restorative procedures. There is a paucity of evidence in relation to the influence of specific restorative procedures on the outcome of root canal re-treatment. In view of this, the following clinical trials are needed: a comparison of the survival of teeth following primary root canal treatment and re-treatment; a comparison of the survival of root canal re-treated teeth restored with different techniques (for example, fiber vs. metal posts); and a comparison of the survival of root canal re-treated teeth with varying degrees of tooth structure loss.

This paper provides a review of clinical protocols and emphasizes the importance of follow-up for re-treated teeth. A clinically useful strategy is presented for review of non-surgical and surgical re-treatments based on best available current evidence.