Comparative evaluation of the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files in severely curved root canals.

AIM: To compare the shaping ability of ProTaper Next, iRaCe and Hyflex CM rotary NiTi files during the preparation of severely curved root canals in extracted human molar teeth. METHODOLOGY: Sixty mandibular molars with mesio-buccal canals having angles of curvature ranging from 25 degrees to 35 degrees were divided according to the instrument used into three groups of 20 teeth each: group PTN (ProTaper Next), group IR (iRaCe) and group HF (Hyflex CM). Using standardized pre- and post-instrumentation radiographs, straightening of canal curvature was determined using image analysis software. A double-digital standardized radiographic technique was used to determine apical transportation 0.5 mm from the working length (1.5-mm coronal of the major foramen). Preparation time and instrument failures were also recorded. Data were analysed using one-way analysis of variance (anova) and post hoc Tukey's test, and significance was set at P < 0.05. RESULTS: During root canal preparation, no instruments fractured. The use of PTN resulted in significantly greater canal straightening than IR and HF (P < 0.05), with no significant differences between IR and HF (P > 0.05). There were no significant differences between the three groups with respect to apical transportation (P > 0.05). IR and HF were significantly faster than PTN (P < 0.05), with no significant differences between IR and HF (P > 0.05). CONCLUSIONS: Under the conditions of this study, PTN, IR and HF respected original canal curvature well and were safe to use.