Comparison of preparation of curved root canals with Hyflex CM and Revo-S rotary nickel-titanium instruments.

AIM To compare the shaping ability of three different nickel-titanium rotary instruments during the preparation of curved root canals in extracted teeth. METHODOLOGY A total of 60 root canals with curvatures ranging between 25° and 35° were divided into three groups of 20 canals. Based on radiographs taken prior to instrumentation, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared to a final apical size of 35 using Mtwo, Hyflex CM, and Revo-S. Using pre- and post-instrumentation radiographs, straightening of the canal curvatures was determined with a computer image analysis program. Preparation time, changes of working length and instrument failures were also recorded. These data were analysed statistically using anova and Student-Newman-Keuls test. RESULTS During preparation, no file fractured. Mtwo and Hyflex CM maintained the original canal curvature significantly better than Revo-S (P < 0.05). Instrumentation with Mtwo and Hyflex CM was significantly faster than with Revo-S and resulted in less loss of working length (P < 0.05), whilst no significant differences were obtained between Mtwo and Hyflex CM (P > 0.05). CONCLUSIONS Under the conditions of this study, Mtwo and Hyflex CM respected the original canal curvature well and were safe to use. The use of Revo-S instruments required more time to prepare the curved canals and resulted in more pronounced canal straightening compared with Mtwo and Hyflex CM.