2.2. Sample Selection and Preparation
dehydration
DEHYDRATION, SMEAR LAYER
This experimental in vitro study was approved by the Institutional Ethics Committee (IRB-942/DUHS/Approval/2019/163). A total of 110 sound mandibular premolars with mature apices, straight roots and a single canal system, which were extracted due to orthodontic or periodontal reasons, were selected for the study. Following extraction, teeth were ultrasonically cleaned of all debris and stored in 0.1% thymol solution until further procedure.Preparation of all samples was performed by the principal investigator. To prevent dehydration, samples were held in a moistened piece of gauze. Crowns were sectioned using a diamond disk with a water coolant attached in a slow-speed handpiece (Nakanishi, Japan) to obtain a standardized root length of 15 mm ± 1 mm. All samples showed a visible canal orifice through which #10 K-file (MANI, Japan) was inserted to check patency. Working length was determined by inserting a #15 K-file and subtracting 1 mm from the length when the file tip was visible at the apex. After a reproducible guide path was established, canal preparation was performed using the crown-down technique with the Endosequence filing system (Brasseler, USA) at 600 rpm and 2.0 Ncm torque settings. Complete cleaning and shaping were performed to tip size 30/0.04 taper. Irrigation was performed with 5.25% NaOCl. After preparation was complete, samples were irrigated with 5 mL of 17% EDTA for 1 min to remove the smear layer. Finally, the canals were flushed with 2 mL of distilled water for 1 min and dried with paper points (Brasseler, USA).