Group 6- Passive ultrasonic irrigation (PUI): Irrigation protocol was the same as Group 3, with the exception that the passive ultrasonic activation was performed using an Irrisafe ultrasonic tip (size 25, 0.02 taper) (Satelec Acteongroup, France) that was placed 1 mm short of the WL. A power setting of 9 was used for duration of 1 min. A 10 mL 2.5% NaOCl solution continuously delivered at a flow rate of approximately 0.16 mL s-1through the unit.