## 2 Case Report
### Case 2  
A 16-year-old girl was referred for the nonsurgical endodontic retreatment of the maxillary left central incisor (21) with pulp necrosis and chronic apical periodontitis with the presence of a long-standing sinus tract and a previous endodontic treatment failure. The periapical radiograph and CBTC revealed the maxillary left central incisor with pulp chamber and the canal underfilled with core material and a mineralized tissue beyond the tooth apical portion, separated from the root (Figure 3A,B and Supplementary Materials: Video S2). The agenesis of several teeth was confirmed (12, 22, 32, and 42) with the patient records. Previous dental trauma (non-specified on the parent's records) on tooth 21 at age 7, followed by an attempt of REP by a generalist dentist, two years before the visit was referred by the child parents. However, the patient remained with edema, swelling, and a sinus tract associated with tooth 21. At the day of evaluation, tooth 21 had normal periodontal probing, and response to sensibility tests (thermal and electrical pulp testing) was negative. After an extended discussion with the children parents about the several treatment options, a nonsurgical root canal retreatment with an apical barrier with a biomaterial (BiodentineTM, Septodont, Saint-Maur-des-Fosses Cedex, France) was elected. At the first appointment, anesthesia was performed with 3% mepivacaine (Mepivastesin(r), 3M ESPE, Neuss, Germany) and under the rubber dam, an access cavity was made with a diamond bur (size #12, Dentsply Sirona, Ballaigues, Switzerland) and refined with an Endo-Z drill (Dentsply Maillefer, Ballaigues, Switzerland). After accessing the pulp chamber, a previous root filling was removed under magnification. Then, a long-neck (LN) bur (size #10, Dentsply Sirona, Ballaigues Switzerland) and an ultrasonic tip (size #3, Start-XTM, Dentsply Sirona, Ballaigues Switzerland) were used to remove the hard material from the canal walls, which was similar to a hydraulic silicate cement (Figure 3C). The same tip was used for ultrasonic agitation of the irrigant. After minimal manual instrumentation with a K-file (size #50, Dentsply-Maillefer, Balaigues, Switzerland) of the canal walls, the disinfection procedure was achieved with copious irrigation of 3% sodium hypochlorite (NaOCl; CanalProTM, Coltene/Whaledent, Langenau, Germany). Intracanal medication (45% CH, Calcicur) was placed in the coronal portion of the canal (Figure 3C) and the access cavity closed with a temporary restorative material (CavitTM). Three weeks later, the tooth (21) was asymptomatic, and no edema or sinus tract were observed. In the second session, local anesthesia was performed with 2% lidocaine with 1:100,000 epinephrine (XylesteinTM 2%, 3M ESPE, Neuss, Germany), a rubber dam placed, and the provisional material was removed. Figure 2: Case report 1 with controls radiographic images: (**A**) 12-month postoperative periapical radiograph control of tooth the continuity of the periodontal ligament space with absence of apical radiolucency was observed at radiographic evaluation showed appreciable root length increase; (**B**) after 2 years; (**C**) a total root formation is observed in radiographs after 3-years; (**D**) at the 5-year follow-up, an increase was observed in the root length and thickness and a decrease of the root canal lumen width. The intracanal medication was removed with continuous irrigation of 3% sodium hypochlorite (NaOCl; CanalProTM, Coltene/Whaledent, Langenau, Germany) and saline solution. The canal was dried with paper points and a bioceramic material (BiodentineTM) was prepared in accordance with the manufacturer's instructions. It was smoothly carried into the canal and compacted apically with a hand barrier (size #2, Buchanan Hand Plugger) to form an apical barrier of 5 mm in thickness. The excess of material from the walls was removed with paper points, a moist cotton pellet was added, and the access cavity was temporarily closed (CavitTM).