Efficiency of rotary nickel-titanium K3 instruments compared with stainless steel hand K-Flexofile.: Part 2.: Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth

Aim To determine the cleaning effectiveness and the shaping ability of K3 nickel-titanium rotary instruments and stainless steel hand K-Flexofiles during the preparation of curved root canals in extracted human teeth. Methodology A total of 60 root canals of mandibular and maxillary molars with curvatures ranging between 25degrees and 35degrees were divided into two groups of 30 canals. 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 by K3 instruments using a crown-down preparation technique or by K-Flexofiles using a reaming motion up to size 35. After each instrument, the root canals were flushed with 5 mL of a 2.5% NaOCl solution and at the end of instrumentation with 5 mL of saline. 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 were quantified on the basis of a numerical evaluation scale, using a scanning electron microscope. The data established for scoring the debris and the smear layer were separately recorded and analysed statistically using the Wilcoxon's test. Results None of the stainless steel K-Flexofiles but 5 K3 nickel-titanium instruments separated. Completely clean root canals were never observed. For debris removal, K-Flexofiles achieved significantly better results (P < 0.001) than K3 instruments. The results for remaining smear layer were similar (P > 0.05). K3 instruments maintained the original canal curvature significantly better (P < 0.0001) than K-Flexofiles. 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, K-Flexofiles allowed significantly better removal of debris than K3 instruments. K3 files maintained the original curvature significantly better. A number of K3 instruments fractured