-Case 1 A 22-year-old, healthy female was referred for endodontic treatment of the maxillary left lateral incisor. The chief complaint was pain when biting and the presence of a sinus tract. The patient could not recall any causative traumatic event in her dental history. Changes in the occlusal anatomy were observed concerning the contralateral tooth (presence of palatal invagination and different incisal anatomy). A sinus tract between teeth #10 and #11 was observed, but the tooth was caries free. Gingival probing depths were within normal limits. The tooth was sensitive to palpation and percussion and failed to respond to cold sensitivity testing, while the adjacent teeth all responded to the same tests within normal limits. Periapical radiographs demonstrated a radiolucent lesion in the apical third of the left lateral incisor consisting of a radiopaque image inside the crown resembling a dens in dente and a widening of the canal consistent with advanced internal root resorption. Another radiograph was taken with a size 30 gutta-percha cone through the sinus tract, pointing to the apical region of this tooth. A clinical diagnosis was established of pulp necrosis with chronic apical abscess, dens invaginatus type 2, and internal root resorption. The primary purpose of treatment was to remove the infection and allow periapical healing. After obtaining informed consent, the tooth was isolated with a rubber dam and access was gained to the pulp chamber, eliminating the invagination. Working length (WL) was established using a size 80 K-file and an electronic apex locator (Root ZX Mini, JJ Morita) to 17 mm. No instrumentation was applied so as not to further widen the canal, but irrigation with 5.25% sodium hypochlorite (NaOCl) solution was used. For the final irrigation, 1 mL of 17% EDTA (Irri-S; VDW) ultrasonically activated in three 20-second cycles, and a final irrigation with 5.25% NaOCl was performed. Root canals were dried with paper points size 80/.02 (Dentsply Maillefer). During the one-session treatment, mineral trioxide aggregate (MTA) was placed using ultrasonic activation of a plugger in the apical third of the canal, followed by backfill with gutta-percha (SuperEndo B&L-alfa, B&L Biotech) and a temporary filling of the access cavity (Cavit. 3M ESPE AG Dental Products). The final restoration of the tooth was completed using composite in a second session, with follow-ups after 6 months, and 1, 2, 4, and 8 years. -Case 2 A 40-year-old, healthy male was referred for endodontic treatment of the maxillary right lateral incisor. Chief complaint was pain when biting. The patient could not recall any pertinent event in his dental history. Presence of a palatal restoration was observed during exploration, but the tooth was caries free. Gingival probing depths were within normal limits. The tooth was sensitive to palpation and percussion and failed to respond to cold sensitivity testing, while the adjacent teeth all responded within normal limits to the same tests. Periapical radiographs showed a radiolucent lesion in the apical third and a radiopaque image inside the crown resembling a dens invaginatus and a widening of the apical third of the canal. These were consistent with internal root resorption. The maxillary left lateral incisor showed normal anatomy. A clinical diagnosis was established of pulp necrosis with apical periodontitis, dens invaginatus type 2, and internal root resorption. The primary purpose of treatment was to remove the infection and allow periapical healing. After obtaining informed consent, the tooth was isolated with a rubber dam and access was gained to the pulp chamber, eliminating both the restoration and the invagination. WL was established using a size 15 K-file and an electronic apex locator (Root ZX Mini, JJ Morita) to 25 mm and instrumented with the Proper Next system (Dentsply Maillefer) to an apical size 30. A solution of 5.25% NaOCl was used during this session. Calcium hydroxide was placed and left for a second appointment. After 15 days, during the second treatment session, irrigation with 5.25 % NaOCl was carried out; for the final irrigation, 1 mL of ultrasonically activated 17% EDTA (Irri-S; VDW) in three 20-second cycles, with a final irrigation with 5.25% NaOCl were used. Root canals were dried with paper points size 30/.02 (Dentsply Maillefer). MTA was placed using ultrasonic activation of a plugger in the apical third of the canal (17) followed by backfill with gutta-percha (SuperEndo B&L-alfa, B&L Biotech) and a final restoration of the access cavity with composite. The tooth was reexamined after 5 months, 2 years, and 3 years. -Case 3 An 18-year-old, healthy female was referred for endodontic treatment of the maxillary left lateral incisor in 2011. Chief complaint was pain when biting and on palpation at the buccal vestibule. A palatal groove was observed in the palatal surface but probing depths were all within normal limits and the tooth was caries free. The tooth was non-responsive to cold sensitivity testing while all other teeth that were tested responded within normal limits to the same tests. Periapical radiographs showed a radiolucent lesion in the apical and middle thirds of the root, a radiopaque image inside the crown resembling a dens-invaginatus and a widening in the middle third of the root canal consistent with internal resorption The diagnosis was pulp necrosis with apical periodontitis, dens invaginatus type 2 and internal root resorption. After obtaining the informed consent, the tooth was isolated with a rubber dam and access was gained to the pulp chamber. WL was established using a size 20 H-file and an electronic apex locator (Elements diagnostic, Sybron Endo, Orange CA) and instrumented with Twisted files (Sybron Endo) to an apical size 40/06. A solution of 5.25% NaOCl was used during this session. Calcium hydroxide was placed and left for a second appointment. After 7 days, during the second treatment session, irrigation with 5.25 % NaOCl was carried out and activated with an ultrasonic tip at 2 mm from WL, then; for the final irrigation, 1 mL of 17% EDTA was used intracanal for 1 minute. Root canals were dried with sterile paper points and the canal was filled with continuous wave of condensation in the apical third, and then a back fill with the extruder and gutta-percha using the Elements Obturation device (Sybron Endo). A final restoration of the access cavity with composite was done by the referral dentist. The patient returned 8 years later for a consultation wishing to change the composite restoration on the tooth. She mentioned that she had remained asymptomatic ever since the root canal was finished. The patient was referred to have a new composite placed.