A 26-year-old female patient was admitted to the Department of Endodontics…, in December 2019. She was referred for evaluation of the left mandibular second molar with the chief complaint of intermittent pain and occlusal pain in this tooth. The patient denied having a remarkable medical history or drug allergies, and she reported caries for which her dentist filled as restoration. Upon extraoral examination, no significant signs were noted. The intraoral examination revealed that the left mandibular second molar (#37) had been restored with white material (Figure 1A) and showed no signs of swelling, no response to the pulp test, and no pathological mobility. Periodontal probing around the tooth showed a pocket within physiological limits without an intraoral sinus. However, there was severe pain from percussion and palpation. The first mandibular molar had a crown and no response to the cold test or percussion and was asymptomatic. Radiographic examination showed that tooth #37 had a large periapical radiolucency encompassing both the mesial and distal regions with a size of 11×6×6 mm³ (Figure 1B), which was confirmed by CBCT (Planmeca Romexis,Finland) (Figure 1D, E). In addition, the root canals in tooth #37 had two roots: The mesial root had two separate canals, the distal root had an oblate canal (Figure F-G), and a large periapical radiolucency that perforated the lingual cortical plate was observed in the apical region of #37 (H-I). More importantly, all canals in both the mesial and distal roots had a sharp curvature mainly in the distal direction. Referring to the method of canal curvature, namely, the Pruett method[10], the degree of root canal curvature was measured using periapical radiographs, which showed that the curvature was mainly in the distal direction. The degree of curvature in the mesial and distal root was determined to be 91.5 (α) and 105 (β) degrees, with radii of curvature of 3.2 mm (r1) and 3 mm (r2), respectively (Figure 1C), indicating that the canals were severely curved, which makes treatment difficult. According to clinical and radiographic examination, a diagnosis of chronic periapical periodontitis of #37 was reached, and a nonsurgical treatment (RCT) of the tooth was proposed and scheduled.
After discussing possible treatment options, the patient agreed to treatment for tooth #37 and signed the informed consent form. The tooth was isolated with a rubber dam, and the old fillings were removed before completely exposing the top pulp chamber. Endodontic access was completed using a diamond bur with a water spray. The entire procedure was performed under a dental microscope (ZUMAX, Suzhou, China) and with the guidance of CBCT. Three canals were identified, namely, the mesiobuccal, mesiolingual and distal canal under magnification, and a Ni-Ti file rotary system (Orodeka, PLEX, Italy) was used for root canal preparation. The preparation and process of cleaning and shaping the canals was divided into two parts: (1) During the initial stage of RCT, the orifices of the root canals were trimmed using ET18D (ACTEON®, SATELEC, France), and coronal access was obtained using #15/08 (Orodeka, PLEX, Italy). (2) For mesial root canals, after exploring and dredging the position of the canals with #08 and #10 K-files (Densply, USA), the initial working length (WL) was determined by #10 K-files at the end of the apex under magnification, which was confirmed by periapical radiographs (Figure 2A-D). Then, canals were shaped and enlarged using #15/03, #20/04 and #25/04, while for a distal root canal, the upper canal was used for the crown-down technique with #15/03, #20/04 and #25/06 according to the resistance. After that, #6 K-files was established a straight path to the apex with EDTA gel (MD-ClelCream, Meta Biomed, USA)), and the WL was determined according to the penetration of the #06 K-files and measured (referring to the point on the crown edge to the apical foramen minus 1 mm)[11]. The step-back technique, using the 0.5-mm recession method with #08, #10 and #15 K-files, was used for apex preparation to maintain the original morphology and shape of the root canal. Finally, the canal was finished with #12/03 and #15/03. A total of 20 ml of 5.25% NaOCl combined with 17% EDTA solution was used to irrigate every root canal during preparation. An ultrasound system (P5 Newtron XS, SATELEC, France) was introduced to activate the irrigant, and a photon-initiated photoacoustic streaming (PIPS) technique (Er:YAG, SSP, 2 Hz, 20 mJ, 0.15 W, LightWalkerAT, Fotona, Germany) was used to further remove the deep smear layer and eliminate any remaining bacteria in the dentin canal tubes. Finally, paper points were used to dry the canals for inspection, calcium hydroxide paste was used as filler, and then the coronal was temporarily sealed with temporary filling material (Ceivitron, Taibei, China). All operations were carried out successfully under a dental operating microscope.
The tooth was re-examined two weeks later, and the canals were copiously irrigated with 17% EDTA solution to remove calcium hydroxide paste. After cleaning with the PIPS technique and distilled water, the canals were dried with paper points. The main gutta-percha cones were selected (#25/04), and the mesial canals were filled with large taper gutta-perchas and root canal sealer iRoot® SP (Innovative Bioceramix, Vancouver, BC, Canada). However, gutta-perchas could not reach the WL point in the distal canal due to the sharp curved apex. Therefore, the vertical condensation technique was used for the apical sites, in which iRoot® BP Plus (Innovative Bioceramix, Vancouver, BC, Canada) was placed as a barrier to exert a better apical sealing effect after filling with iRoot® SP (Figure 2E). Postoperative radiographs were taken to confirm that three canals were filled compactly, especially in the curved corners. After three months of observation (Figure 3B), the patient had no spontaneous pain or other obvious abnormalities, and the tooth was restored with composite resin (Filtek Z350 XT, 3M ESPE). The patient was then referred for restorative treatment. The edge of the ceramic crown and occlusal was checked to ensure a proper fit (Figure 2G-I), and follow-ups were recommended after one year. No pain, swelling or mobility were noted. The radiographic examination of the treated tooth confirmed the almost complete recovery of periapical radiolucency, suggesting that the periapical inflammation healed obviously at six months and one year postoperatively (Figure 3C-H).