For each specimen, 11 mL of 2.5% NaOCl was used as irrigation solution and was delivered at a flow rate of approximately 0.08 mL s-1 except for G6 (PUI). The irrigant was delivered into the canal with a double side-vented needle (i dental, Lithuania) except for Group 1 (beveled needle). The amount of remaining CH in the grooves was evaluated under a stereomicroscope (Zeiss Stemi 2000-C, Germany) at 20× magnification and equipped with a digital camera (AxioCam ERc5s, Germany) by two calibrated endodontists using an numeric evaluation scale described by van der Sluis, et al.30 (2007). The scoring system was as follows: score 0, the groove is entirely empty; score 1, CH is present in less than 50% of the groove; score 2, CH is present in more than 50% of the groove, but not completely; and score 3, the groove is completely covered with CH (Figure 2). Evaluation was conducted based on the color codes by two endodontists blinded to the group number. Before scoring, the two endodontists assessed 50 randomly selected specimens simultaneously for calibration purposes. In the case of discrepant scores, a consensus was reached by discussion.