Apical transportation and canal straightening with different continuously tapered rotary file systems in severely curved root canals: F6 SkyTaper and OneShape versus Mtwo

To compare apical transportation and canal straightening when using three continuous tapered rotary NiTi systems [F6 SkyTaper (Komet/Brasseler, Lemgo, Germany), Mtwo (VDW, Munich, Germany) and OneShape (Micro Méga, Besançon, France)] in severely curved root canals.A total of 60 root canals in extracted human teeth with angles of curvatures ranging between 25° and 35° and radii ranging between 4 and 9 mm were divided into three groups (n = 20). Based on radiographs taken prior to instrumentation, the groups were balanced with respect to the angle and the radius of canal curvature (P = 1.0 and P = 0.994, respectively). All canals were prepared to an apical size 30 according to the manufacturer's instructions. Pre- and post-instrumentation radiographs were superimposed and apical transportation and canal straightening were analysed using a computer imaging program. Preparation time and instrument failure were also recorded. Data were analysed statistically using anova and Student-Newman-Keuls test.During preparation, no file fractured. All instruments maintained the original canal curvature well with no significant differences between the instruments (P = 0.542). Concerning apical transportation, no significant differences were obtained (P = 0.414). Regarding preparation time, no significant differences were obtained between F6 SkyTaper and OneShape (P > 0.05), but both were significantly faster than Mtwo (P < 0.05).Under the conditions of this study, all instruments respected the original canal curvature well and apical transportation was negligible. Instruments were safe to use. Preparation with F6 SkyTaper and OneShape was faster than with Mtwo.