Navitip

Working lengths of the 120 roots in the experimental groups were determined by subtracting 1 mm from the length at which the #10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) first appeared at apical foramen. Then, the apical foramen of each canal was sealed with sticky wax to create a closed-end system.
Root canal preparation was initiated with glide path management by manipulating ProGlider instrument (tip size/taper: #16/.02) (Dentsply Sirona, York, PA, USA) at 300 rpm and a torque of 4.0 Ncm to full working length. Then, the root canals were shaped by using ProTaper Gold NiTi instruments to F4 (tip sizes/taper: #40/0.06) (Dentsply Sirona). The files were powered by an electric motor (X-Smart plus, Dentsply Maillefer) with the manufacturer’s recommendations. Throughout the period, 2 mL 5.25% NaOCl (except for the MTAD groups, where 2 mL 1.3% NaOCl was used) (all manufactured by Wuhan Longly Biotechnology Co., Ltd., Wuhan, China) was used as an intracanal irrigant solution by using a 30-G side-vented needle (Navitip, Ultradent, South Jordan, UT, USA) after each instrument. After the preparation, the canals were irrigated with 5 mL distilled water to rinse out NaOCl and dried with #40 paper points (Dentsply Maillefer).

All the canals were enlarged to 30 0.06 using Protaper gold rotary files. An automated root canal irrigation device was coupled to a disposable plastic syringe with an attached 30-gauge side-vented needle (NaviTip, Ultradent Products, South Jordan, UT, USA) for irrigation in between and at the completion of the instrumentation process. The entire irrigation procedure was identical to group 1, but it was performed using an automated irrigation system [37 (link)]. Following the completion of the entire irrigation technique, the crown portion was decoronated at the cement–enamel junction (CEJ). Additionally, using a microtome LEICA SP 1600 (Wetzlar, Germany), the roots were separated bucco-lingually. The root was sputter-coated with gold and examined under scanning electron microscopy (SEM).
Using the scoring system developed by Hülsmann et al. [38 (link)], the debris and smear layers were examined independently and scores ranging from 1 to 5 were given [39 (link)] (Table 1 and Table 2). The debris and smear layer were evaluated separately using reference images and a five score-index for each. All of the samples were scored by two unbiased evaluators (KJ and KVT) using calibration data for debris and smear layer scores. In 1000× magnification, the debris and smear layers were scored (Figure 1).