Instrumentation of curved root canals: a comparison study.

Flex-R, Flex-O, and K-Flex files were compared using a circumferential filing technique on 30 extracted human molars. The buccal canals of maxillary molars and mesial canals of mandibular molars were utilized. The minimal initial curvature was 18 degrees. Canal curvature was measured before and after filing, and changes were analyzed statistically. Analysis showed that, no matter which of the instruments was used, the angle of curvature was maintained with a high degree of accuracy.