Effect of passive ultrasonic irrigation Ballaigues, Switzerland). The remaining canal another minute. This sequence was repeated space was shaped in a crown-down manner with three times, resulting in a total PUI time of three ProTaper instruments (Dentsply Maillefer), and minutes. The volume of extruded irrigant was apical instrumentation at WL was completed with measured as mentioned for the control group. an F3 file (ISO size 30, taper 0.09-0.05). Between The data were statistically analyzed with the the instruments, each canal was irrigated with 2 Mann-Whitney U test, and P was set at .05. mL of a 2.5% NaOCl solution using a syringe and RESuLtS a 27-gauge needle. Apical patency was checked with a size 10 K-file between each instrument. Table 1 presents the mean volume and After preparing the root canal, the method standard deviations of irrigant extruded for that Myers and Montgomery36 recommended each group, and the range of volume extruded was used to determine the amount of solution (minimum and maximum values). The mean extruding from the apical foramen during the PUI volume of apical extruded irrigant was 2.15±2.73 as a final irrigation. Each sample was attached µL for the PUI group and 14±13.03 µL for the to a rubber stopper, and root apexes that would control group. The experimental group extruded fit into a 4 mL centrifuge tube were placed into significantly less irrigant than the control group a glass bottle together with the tube. In order (P<.05). to equalize the air pressure in and outside the dISCuSSIoN bottle, a 23-gauge needle was inserted into the bottle through the rubber stopper (Figure 1). A method different from the routine clinical Group 1 (control group): The canal was filled practice was applied in this in vitro study. That with 2.5% solution of NaOCl using a syringe and is, in a clinical setting, the root canal is generally a 30-gauge irrigation needle with a side opening and a rounded tip (KerrHawe SA, Bioggio, Switzerland) which penetrated to within 1 to 2 mm from the working length.. After one minute, if there was extrusion from the apical foramen and the amount of irrigant in the canal was reduced, the canal was refilled with irrigant. This sequence was repeated three times resulting in a total irrigation time of three minutes. At the end of this period, each tooth was removed from the centrifuge tube and the centrifuge tube was removed from the vial. The volume of extruded irrigant was measured by Pipetman pipettes (Gilson, Inc., Middleton, WI, USA). Group 2 (experimental group): The same teeth used in Group 1 were also used in group 2 after their canals were completely dried with absorbent paper points. After the root canal was filled with 2.5% NaOCl solution, using the same syringe and irrigation needle used for the control group, PUI was performed with a piezoelectrical ultrasonic unit (NSK Varios 750, Nakanishi, Tochigi, Japan). A stainless steel instrument (size 15) (Varios U files) was inserted into the root Table 1. The mean volume of extruded irrigant (µL). canal 1 mm short of the WL, and the irrigant was ultrasonically activated for one minute. After the n Minimum Maximum reduced amount of irrigant was supplemented, Control 20 0 35.0 the irrigant was reactivated ultrasonically for PUI 20 0 8.0 Figure 1. Irrigant extruded through the apical foramen was collected in a centrifuge tube. Mean±SD 14.00±13.03 200 European Journal of Dentistry 2.15±2.73