An initial investigation on torsional properties of nickel-titanium instruments produced with a new manufacturing method.

A new manufacturing process involving twisting of a ground blank combined with heat treatment has been recently developed to produce nickel-titanium rotary files for root canal preparation. The aim of this study was to compare torsional resistance of prototype instruments produced using the new manufacturing method versus traditional nickel-titanium instruments produced by the customary grinding process. Twenty prototypes instruments of the same design and dimensions were divided in two groups of 10 each, according to the different manufacturing method. A file-testing apparatus specifically designed to perform torsional testing was used in accordance with the International Organization for Standardization 3630-1. The results indicated that instruments manufactured by the new manufacturing process demonstrated significantly higher average maximum torque levels than those manufactured by the existing grinding process (P < 0.05). Since instruments design and dimensions of the instruments were the same, the different manufacturing process could be the only explanation for this improvement in torsional resistance.