Study design
3.1.9.2, calculus
All procedures performed were carried out in accordance with relevant guidelines, regulations and ethical standards of the ethical committee of research of the Faculty of Dentistry, Suez Canal University (approval number for the study: 137/2018.)This study was a single-blinded study, conducted on 60 human mandibular first molar teeth extracted for periodontal reason, extracted teeth were collected from the outpatient clinics after approval of the patient. The sample size was calculated according to G*Power software version 3.1.9.2 at a significance level of Teeth were rinsed under running water, then an ultrasonic scaler was used to remove calculus and soft tissue remnants from the root surface, then immersed in 5.25% NaOCl (Clorox, Egyptian Company for household cleaners, Cairo, Egypt) for 10 min for disinfection then stored in distilled water at room temperature till the time of the study. The experimental setup followed the technique described by Klyn et al. which used a copper cube based on the Bramante model [All roots were cut by a diamond disc (Isomet 4000 linear precision saw, Buehler, Lake Bluff, IL, USA) to establish a unified length of 12 mm for all roots for the purpose of standardization, to eliminate the variable of root canal length on the cleaning efficiency between groups.Roots were scanned using cone beam computed tomography (CBCT) unit Scanora 3Dx (Kavo Dental, Germany) with exposure parameters; 90 kVp and 4 mA to detect the presence of a type V isthmus (complete anastomoses between both canals) at 2,4 and 6 mm from the apex and those with a partial connection or without an anastomosis or were replaced. Also, CBCT was also employed to exclude teeth internal or external root resorptions, calcified root canals, open root apices and to measure the angles of roots curvature using the Schneider technique [