Influence of Kinematics on the Cyclic Fatigue Resistance of Replica-Like and Original Brand Rotary Instruments.

ABSTRACT Introduction To evaluate the cyclic fatigue resistance of 3 replica-like rotary instruments compared to their original brand systems using continuous rotation and optimum torque reverse (OTR) kinematics. Methods New F1 rotary instruments (n=20 per group) from ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) and ProTaper Gold (Dentsply Maillefer) original brand systems were compared to 3 replica-like instruments (U-File, Dentmark, Ludhiana, India; Super Files, Shenzhen Flydent Medical, Shenzhen, China; and Super Files Blue, Shenzhen Flydent Medical) regarding cyclic fatigue resistance. In each group, the selected instruments were randomly distributed into two subgroups (n=10), according to the kinematic. In the rotary group (ROT), the instruments were activated with a continuous clockwise rotation (300 rpm, 1.5 N.cm), while in the OTR group, the asymmetric oscillatory motion was performed setting the OTR function at 300 rpm and adjusting the torque limit at minimum level, using the TriAuto ZX2 motor (J. Morita, Kyoto, Japan). The time to fracture was recorded and statistically compared according to the kinematics (ROT x OTR) and the instrument type (replica-like x original brand) using the independent sample t-test (α=0.05). Additionally, the metal alloy characterization of each system was performed by differential scanning calorimetry (DSC) and energy-dispersive X-ray spectroscopy (EDS). Results Statistical analysis revealed significantly higher time to fracture for all rotary systems tested in the OTR motion compared to continuous rotation (P Conclusions OTR motion significantly improved the fatigue resistance of both original and replica-like systems. The replicas showed higher cyclic fatigue resistance than original brand instruments and higher transition temperatures to austenitic phase.