Comparative investigation of two rotary nickel-titanium instruments:: ProTaper versus RaCe.: Part 2.: Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth

Aim To determine the cleaning effectiveness and shaping ability of ProTaper and RaCe nickel-titanium rotary instruments during the preparation of curved root canals in extracted human teeth. Methodology A total of 48 root canals of mandibular and maxillary molars with curvatures ranging between 25degrees and 35degrees were divided into two groups of 24 canals each. Based on radiographs taken prior to instrumentation with the initial instrument inserted into the canal, the groups were balanced with respect to the angle and the radius of canal curvature. Canals were prepared using a crown-down preparation technique. After each instrument, the root canals were flushed with a 2.5% NaOCl solution and at the end of instrumentation with NaCl. Using pre- and post-instrumentation radiographs, straightening of the canal curvatures was determined with a computer image analysis program. After splitting the roots longitudinally, the amount of debris and smear layer was quantified on the basis of a numerical evaluation scale, using a scanning electron microscope (SEM). The data established for scoring the debris and the smear layer were separately recorded and analysed statistically using the Wilcoxon test. Results Two ProTaper and three RaCe instruments fractured; there was no significant difference between instrument types (P > 0.05). Completely clean root canals were never observed. For debris removal, RaCe files achieved significantly better results (P < 0.001) than ProTaper instruments. The results for remaining smear layer were similar and not significantly different (P > 0.05). RaCe instruments maintained the original canal curvature significantly better (P < 0.05) than ProTaper instruments. No significant differences were detected between the instruments (P > 0.05) for the time taken to prepare the canals. Conclusions Under the conditions of this study, RaCe instruments resulted in relatively good cleaning and maintained the original curvature significantly better than ProTaper did.