Effect of curvature angle and rotational speed on fracture of various Ni-Ti rotary files used in extracted molars

Objectives: The objective of this study was to evaluate the effect of rotational speed and angle of curvature in curved root canals on the fracture of different nickel-titanium rotary instruments that is Profiles, ProTaper, and K 3 files. Materials and Methods: Freshly extracted 180 human maxillary and mandibular molars were selected and divided into two groups of 90. Each group was then divided into three sub groups A, B, and C according to angle of curvature, Group I < 30° and Group II > 30°, which was measured by Schneider′s method. Instrumentation was performed using the profile, ProTaper, and K3 (Company and in Literature name of Rotary file is K3) rotary instrument at 3 rotational speeds of 150, 250, and 350 rpm (10 molars at each rotational speed). Results: There were total of 32 instrument fractured out of 120 files. In a multivariable analysis, it was demonstrated that the rotational speed of 350 rpm fractured than those used at 150 rpm (odd′s ratio [OR]: 3.6, 95% confidence interval [CI]: 1.3-10.5). An increase in the angle of curvature of the canal did not significantly increase the likelihood of fracture (OR: 1.9, 95% CI: 0.8-4.2). No significant differences were found between various designs of files used. Conclusion: Instrument fracture was associated with rotational speed and the angle of curvature.