Secondary root canal treatment. When, how and why

OBJECTIVES Endodontic retreatment procedures are increasing in clinical practice. The re-treatment aims to maintain a previous-ly treated tooth in which a periapical lesion is detected. Retreatment procedures should remove the previous filling material, provide an effective instrumentation and irrigation of the canal and provide a stable obturation and tooth reconstruction. These procedures are often complex and time consuming. The purpose of this Module is to describe the current endodontic retreat-ment techniques trying to identify their advantages and clinical limitations. MATERIALS AND METHODS The main causes of endodontic retreat-ment are considered, through the de-scription of the endodontic microbiolo-gy and the types of periapical lesions that can be observed in non-healed root canal treatments. The morphology of the endodontic canal after second instrumentation is described and some strategies are considered to remove the old filling material. RESULTS The conditions of endodontic retreat-ment are mainly due to the reinfection of the endodontic space, which can oc-cur due to coronal contamination (loss of the coronal seal) or to the presence of bacterial populations in areas of the canal not instrumented. Some bacteria, such as Treponema denticola and Por-phiromonas gingivalis, are highly pathogenic and are able to systemical-ly spread and reach different anatomi-cal districts, such as the heart, spleen, liver, and brain. One of the main problems of retreat-ment techniques is the possibility of pushing the infected debris of the ma-terial contained in the canal beyond the apex. These infected debris are respon-sible for acute post-operative pain and acute inflammatory phenomena. Ultrasonic instruments can support traditional manual instrumentation techniques and enhance the effect of the ir-rigants. Reciprocating instrumentation techniques can be used in the removal of the obturation material and in the instrumentation of the root canal. Secondary treatment can be surgically performed (endodontic surgery) where coronal access to the endodontic system is not feasible. Endodontic surgery shows high long-term success and survival rates in recent studies. CONCLUSIONS Endodontic retreatment still remains a complex and time consuming tech-nique. The use of ultrasonic instrumen-tation and reciprocating techniques al-low for better removal of the obturation material and a more effective instru-mentation of the canal. Retrograde endodontic surgery is a useful technique for maintaining the endodontical-ly treated element. CLINICAL SIGNIFICANCE The identification of a new periapical lesion, the non-healing and its exacer-bation in an endodontically treated element is attributable to the non-eradica-tion of pathogenic bacteria, or to a new reinfection of the canal space. For this reason, material removal, irrigation and instrumentation techniques play an important role in endodontic retreatment.