Within this presentation the varying histologic and microbiologic conditions of the root canal system that can be present at inception of the endodontic treatment are illustrated. The progression of the pulp degeneration process after pulp penetration by caries biofilm is discussed. It is stressed how vital, although inflamed, pulp tissue does not harbor bacteria, for which reason a sterile instrument separated in a canal with previously vital pulp is unlikely to cause treatment failure. Under such circumstances, depending on the location of the separated segment, attempts to remove it may be more risky than leaving it, and a "wait and see" strategy is indicated. On the contrary, when separation occurs in a canal with necrotic/infected pulp and apical radiolucency, infection control in the whole canal length is prevented. Therefore, attempts to remove the fractured instrument must be undertaken.

Initial root canal therapy does not always result in healing mainly due to bacterial ingress into the root canal system. Retreatment could also result in non-healing regardless of the those attempts to remove intracanal infection unless it is located and removed. Bacteria may persist following the retreatment procedure due to the areas that were inaccessible to instrumentation and irrigation. The literature shows intracanal biofilms are present in the majority of cases with large periapical lesions, and 90% of endodontic refractory cases have biofilms surviving endodontic retreatment in the hard-to-reach areas in the apical third such as apical ramifications and an isthmus. Therefore, the key to success in retreatment is to remove infection in those spaces. In addition, iatrogenic accidents such as separated instruments and ledge formation can also be serious problems leading to failure because of the inability to disinfect the canal system apical to those obstructions. In retreatment those mishaps that can adversely impact the treatment outcomes should be properly managed. Hence, in the online lecture, the ideal non-surgical management of those nonhealing cases will be presented.

This joint online event by Yoshi Terauchi & Domenico Ricucci will be held on the threshold of a major in-person International event by Yoshi Terauchi in Florence, Italy (May 6-7, 2022). If you wish to participate in both events you can deduct the cost of this online meeting from your ticket price of the event in Florence. Once you register for this online event you will receive a personal promo-code to reduce your ticket cost of the Terauchi Endo Days in Italy.