The effect of a new finishing process on the torsional resistance of twisted nickel-titanium rotary instruments.

The process of twisting has been used for decades to fabricate stainless steel instruments, but it was previously thought to be an impractical method for nickel-titanium (Ni-Ti) instrument manufacture A manufacturing method of twisting Nickel-Titanium wire to produce Ni-Ti files has been recently developed: the twisted files (TF). Theoretically, this new manufacturing process should overcome the problems associated with a grinding process, which previously limited instrument strength. Since TF manufacturing process is new and different from grinding, the aim of the present study was to evaluate the effects of a final deoxidation process (Deox) on torsional resistance of TF instruments. Testing was performed in accordance with the International Standard (ISO 3630-1) by comparing 20 TF instruments versus 20 TF prototype instruments produced without the final deoxidation process. Data were collected and statistically analyzed (t-test). Results show that TF instruments withstood 90% more torque (max. torque) than TF prototype instruments manufactured without the deoxidation process (88.7 vs. 53.3 g/cm). This difference was found to be statistically significant at the 0.05 level of significance. Since design and dimensions of tested instruments were the same, the deoxidation process could be the only explanation of the improvement in torsional resistance.