The influence of various automated devices on the shaping ability of Mtwo rotary nickel-titanium instruments

Aim To compare the shaping ability of Mtwo rotary nickel-titanium instruments in simulated curved canals and in curved canals of extracted teeth when set into permanent rotation with two different torque-limited automated devices. Methodology Root canal instrumentation was performed with two different torque-limited automated devices (Mtwo direct handpiece and Endo IT motor) using Mtwo rotary nickel-titanium instruments up to size 35. Simulated canals: 28 degrees and 35 degrees curved canals in resin blocks (n = 20 canals in each group) were prepared. Pre- and post-instrumentation images were recorded and assessment of canal shape was completed with a computer image analysis program. Extracted teeth: a total of 40 curved root canals were divided into two groups, which were balanced with respect to the angle and the radius of canal curvature. Straightening of the canal curvatures was determined with a computer image analysis program. Incidence of canal aberrations, preparation time, changes of working length and instrument failures were recorded both in simulated and real canals and were analysed using the t-test and a chi-square test. Results In simulated canals, instrumentation with Endo IT was significantly faster than with Mtwo direct (P < 0.05). No significant differences between the two devices were noted when all other parameters were assessed (P > 0.05). Only one instrument separated (Mtwo direct) during the enlargement of 28 degrees curved simulated canals. All systems maintained working distance well. Conclusions Both systems respected original root canal curvature well and were safe, indicating that the Mtwo direct handpiece is suitable for preparing curved root canals with the Mtwo instruments.