A comparison of maintenance of canal curvature using balanced-force instrumentation with three different file types.

Forty-five extracted human molar teeth with curved facial or mesial canals were instrumented to a #45 file with three different file types using balanced-force (BF) instrumentation. Pre- and postoperative X-rays were taken, projected, and file location traced to determine the canal curvature according to the method of Schneider. Results showed statistically less reduction in canal curvature with nickel-titanium (NT) files compared with either Flex-R (FR) (p < 0.05) or K-Flex (KF) files (p < 0.0021). There was no significant difference comparing FR with KF files (p > 0.05). Under the conditions of this study, NT files used with the BF technique were significantly less likely to change canal curvature than either FR or KF files when instrumenting curved root canals.