Intervention
tooth

For patients in low-level laser therapy (LLLT) group, laser applicator was positioned 3 mm away from the oral mucosa with beam focused on apical location. Briefly, after the application of the final flush and with the aid of a dental applicator, a 200-mm fiber optic laser tip was placed perpendicular to soft tissue mucosa at the level of the apices of the targeted tooth based on the tooth length taken by the apex locator and confirmed by the working length periapical X-ray. Diode laser exposure (Lite Medics 1.00-Watt serial number 148 Ver. SwvM. 150VS108VT.100) was carried out using a continuous-mode with 10 Hz frequency, 980 nm wavelength, and max power 15 WCW. The tip was applied both at the buccal and the lingual side for 30 s each [For patient in laser-activated irrigation (LAI) group, at the step final step of irrigation, the irrigant was activated with diode laser (Master lase/expert lase, Kavo, Biberach/Riß) (980 nm wavelength and 2.5 W power, frequency of 100 Hz). The optical fiber was introduced 2–3 mm short of the working length and was withdrawn from apical to coronal direction [For mock laser (ML) group: the diode laser tip was positioned similarly as in group 1 without activation (mock laser).After root canal preparation, the root canals were dried with paper points and filled using matched single cones (Meta Biomed Korea) and AD seal sealer (Meta Biomed Korea) was used. Obturation was done using warm vertical compaction.