Mechanical Properties of a Novel Nickel-titanium Root Canal Instrument: Stationary and Dynamic Tests

Introduction: The aim of this study was to describe the mechanical properties both in stationary and dynamic conditions in vitro of the novel TruNatomy (TN; (Dentsply Sirona, Ballaigues, Switzerland) shaping files and compare them with a conventional rotary system, ProTaper Next (PTN, Dentsply Sirona). Methods: Different sizes of 2 types of rotary files, TN and PTN, were compared for their fatigue limit (n = 20 each size) and torsional resistance (n = 6 each size) and subjected to simulated shaping (n = 6 each size). Fatigue limits were determined in a novel fixture including a tapered simulated curved canal (angle = 75 degrees, radius = 5 mm) with a thermal probe and a cooling airstream (minimum of 2 bars) attached to keep the temperature rise below 2 degrees C. Torsional resistance was tested according to ISO 3630-1. Shaping was simulated in plastic blocks with standardized J-shaped curved root canals in a computer-controlled device to register real-time torque and force. Fracture patterns were assessed using scanning electron microscopy. Parametric statistics and Weibull analysis were used to compare groups. Results: The tested sizes for TN were significantly more fatigue resistant and reliable compared with PTN; torsional limits were similar, but twist angles at failure were larger for TN. No instruments fractured during simulated shaping, and the working torque and the threading-in force were significantly lower for TN. Conclusions: This study showed the mechanical properties of both TN and PTN in terms of fatigue limit and torsional resistance and compared them with simulated canal shaping. TN was found to be more fatigue resistant and showed significantly more predicable torque and threading-in force compared with PTN.