Influence of Kinematics on the Cyclic Fatigue Resistance of Replicalike and Original Brand Rotary Instruments

Abstract

Introduction: The aim of this study was to evaluate the cyclic fatigue resistance of 3 replicalike rotary instruments compared with 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 with 3 replicalike 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 2 subgroups (n = 10) according to the kinematics. In the rotary group (ROT), the instruments were activated with a continuous clockwise rotation (300 rpm, 1.5 Ncm), whereas in the OTR group, asymmetric oscillatory motion was performed setting the OTR function at 300 rpm and adjusting the torque limit at the 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 × OTR) and the instrument type (replicalike × 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 and energy-dispersive X-ray spectroscopy.

Results: Statistical analysis revealed significantly higher time to fracture for all rotary systems tested in OTR motion compared with continuous rotation (P < .05) with a mean percentage increase ranging from 52.1% (ProTaper Gold) to 156.7% (U-File). The replicalike instruments showed a significantly higher time to fracture compared with the respective original brand instruments in either ROT or OTR motion (P < .05). Replicas presented austenitic temperatures above the ones displayed by the original brands and an almost equiatomic ratio between nickel and titanium elements.

Conclusions: OTR motion significantly improved the fatigue resistance of both original and replicalike systems. The replicas showed higher cyclic fatigue resistance than original brand instruments and higher transition temperatures to the austenitic phase.

Keywords: Continuous rotation; cyclic fatigue; differential scanning calorimetry; energy-dispersive X-ray spectroscopy; nickel-titanium system; optimum torque reverse motion.