## 2 Case Report  
### Case 1  
An 11-year-old girl was referred for REP of tooth 15. Her medical history was noncontributory. Sensibility tests (heat, cold, and electrical pulp testing) of the tooth 15 were negative, with evidence of coronal restoration leakage. Clinical examination showed that tooth 15 had edema and suppuration with sinus tract (chronic apical abscess), pain with vertical and lateral percussion, no mobility and the probing depth was within normal limits. Radiographically, the root canal was wide with a divergent open apical foramen (Figure 1A). After assessing the possibility of restoring the tooth without intracanal post and explaining all therapeutic alternatives to the patient and guardians, informed consent was obtained, and REP was performed. Local anesthesia was achieved with 3% mepivacaine (Mepivastesin(r), 3M ESPE, Neuss, Germany). After isolation with a rubber dam, restorative material and carious lesions were removed and the access cavity was performed. After access, the wide-open canal was observed by dental microscope (Leica M320 F12, Leica Microsystems, Heerbrugg Switzerland) with 10x magnification depicting that some vital pulp tissue remained inside the root canal. The working length to this vital tissue was confirmed with paper points (size #80, Dentsply-Maillefer, Balaigues, Switzerland) by the presence of bleeding at 15 millimeters (mm). The canal was irrigated with 20 mL of 3% sodium hypochlorite (NaOCl; CanalProTM 3%, Coltene/Whaledent, Langenau, Germany) using a NavitipTM needle (Ultradent Products Inc, South Jordan, UT) at 13 mm, followed by rinsing with 20 mL of a saline solution for 5 minutes (min). The canal was dried with paper points, and intracanal medication of 45% calcium hydroxide (Calcicur Voco, Cukhaven, Germany) (CH) paste was placed into the canal. The access cavity was sealed with a sterilized cotton pellet and CavitTM (3M, Neuss, Germany) and intermediate restorative material (IRM(r), DentsplyDetrey GmgH, Konstanz, Germany). The patient was scheduled for a second visit after 4 weeks. The tooth (15) was asymptomatic during the entire postoperative period, with no sinus tract or edema, and the temporary filling was intact. In the second session, local anesthesia was accomplished with 3% mepivacaine (Mepivastesin(r), 3M ESPE, Neuss, Germany). Under the rubber dam, temporary material and cotton pellet were removed from the access cavity and the canal was rinsed with 20 mL of EDTA 17% (Coltene/Whaledent, Langenau, Germany) for 5 min, followed by irrigation with 5 mL of a sterile saline solution. The root canal space was dried with paper points and a microsurgical suction tip (Roeko Surgitip-endo, Coltene/Whaledent, Langenau, Germany). Subsequently, a manual sterilized k-file (size #25, Dentsply-Maillefer, Balaigues, Switzerland) was introduced until reaching the 15 mm working length and then deliberately pushed 2 mm past the working length to induce bleeding into the canal. After blood filled the canal up to 2 mm bellow cementoenamel junction (CEJ), an absorbable hemostatic gelatin matrix (Spongostan DentalTM, MS0005, Ethicon Inc, New Jersey, EUA) was placed over the blood clot. Finally, a 3 mm mineral trioxide aggregate barrier (ProRoot(r) MTA, Dentsply Tulsa Dental, Johnson City, TN, USA) was placed in the cervical third of the root canal with a coronal barrier (Buchanan Hand Barrierger #2; Sybron Endo, Orange, CA, USA) over the blood clot. After placing a moist cotton pellet over the MTA, the access cavity was sealed with a temporary restoration material (CavitTM) and two weeks later replaced with a resin-based composite (SDRTM flow and Spectrum(r), DentsplyDetrey GmgH, Konstanz, Germany). After REPs, the tooth (15) was asymptomatic without signs of coronal discoloration. Follow-up was successively performed at 3, 6, 12 months, 3 years, and 5 years (Figure 1E,F and Figure 2).