A comparative computational analysis of the mechanical behavior of two nickel-titanium rotary Endodontic instruments

Introduction: A finite element model of two nickel-titanium (Ni-Ti) rotary endodontic instruments (ProTaper and SystemGT; Dentsply-Maillefer, Ballaigues, Switzerland) was developed to investigate the mechanical behavior of these devices and to identify the benefits/limitations of different geometries during instrumentation in various root canals. Methods: Instrument shape, curved root canal geometry, and Ni-Ti alloy pseudo-elastic behavior were investigated in this study using computational techniques. Two different operating conditions were simulated: (1) the file insertion-removal cycle which resembles the standard working condition and (2) the file subjected to a torque in the counter-clockwise direction, which mimics the auto-reverse movement of the instrument when the tip is locked in the canal wall. Results: The simulations of standard and auto-reverse conditions produced bending and torsion loading conditions in the files, respectively. In the standard situation in which different canal shapes were considered, the strains in the SystemGT were generally lower than the strains in the ProTaper and always in the pseudo-elastic range; in only 1 case did the ProTaper overcame the pseudo-elastic range limit. In the auto-reverse situation, a better behavior of the ProTaper was detected. Conclusions: The two simulated conditions highlighted the different mechanical properties of the files; the SystemGT showed slightly better performances under flexural solicitation, whereas the Protaper presented better behavior under torsion solicitations.