In vitro assessment of torque and force generated by novel ProTaper Next Instruments during simulated canal preparation.

INTRODUCTION The purpose of this study was to assess torque and force for simulated canal preparation with a new root canal instrument, ProTaper Next. METHODS Six sets of ProTaper Next Instruments (X1-X5) were used to prepare 36 artificial canals. Files were divided into 6 groups. Different settings of rotations per minute (250, 300, and 350 rpm) and numbers of in-and-out movements to reach working length (3 or 4 insertions [ins]) were applied in each group (250 rpm/3 ins, 250 rpm/4 ins, 300 rpm/3 ins, 300 rpm/4 ins, 350 rpm/3 ins, and 350 rpm/4 ins) by using an automated torque bench. Peak torques (Ncm) as well as positive and negative forces (N) were registered. Analysis of variance and Tukey post hoc tests were applied. Preliminary data for angle and stationary torque at failure were also obtained and compared with peak torque for each instrument. RESULTS Significant differences in peak torque (P < .0001), positive force (P < .002), and negative force (P < .0001) were found for ProTaper Next instruments overall. X2 showed the highest torque with all settings. X5 showed the highest positive force in all groups. X1 and X2 showed the highest negative forces for all groups except for 350 rpm/4 ins. Significantly lower torque (P < .0001) and positive force (P < .007) were measured in the group 350 rpm/4 ins for all instruments except for X4. In contrast, X1 showed a significantly lower negative force for 350 rpm/4 ins. Torque at failure according to American Dental Association no. 28/ISO 36030-1 was lower for X1, X2, and X3 than torque during simulated canal preparation (P < .0001). CONCLUSIONS Under the conditions of this study, using ProTaper Next at 350 rpm and with 4 in-and-out movements resulted in lowest levels of peak torque as well as positive and negative forces.