Comparative study on the shaping ability and cleaning efficiency of rotary Mtwo instruments. Part 1. Shaping ability in simulated curved canals.

AIM To compare the shaping ability of Mtwo instruments with K3 and RaCe instruments. Part 1 of this two-part report describes the efficacy of these nickel-titanium instruments in simulated curved root canals. METHODOLOGY Simulated canals with 28 degree and 35 degree curves in resin blocks were prepared with Mtwo instruments using a single length technique and with K3 and RaCe instruments using a crowndown preparation technique (n = 20 canals in each case). Pre- and post-instrumentation images were recorded and assessment of canal shape was completed with a computer image analysis program. Material removal was measured at 20 measuring points, beginning 1 mm from the endpoint of preparation. Incidence of canal aberrations, preparation time, changes of working length and instrument failures were also recorded. The data were analysed statistically using ANOVA and Student-Newman-Keuls test. RESULTS On an average, canals prepared with Mtwo instruments remained better centred compared with those enlarged with K3 or RaCe instruments. Six RaCe instruments, four K3 files and none of the Mtwo instruments fractured during preparation (P > 0.05). In both of the canal types, Mtwo was significantly faster (P < 0.001). It was possible with all types of instruments to control working length as well. CONCLUSIONS Mtwo instruments prepared curved canals rapidly, respected original canal curvature well and were safe to use.