In vitro study of the torsional properties of new and used ProFile nickel titanium rotary files.

The purpose of this study was to investigate torque and angle of rotation at fracture of new and used.06 ProFile instruments. ProFile sizes 15 to 40 were tested according to American National Standards Institute/American Dental Association Specification #28. Thirty new and used instruments were tested for each size. An analysis of variance was used to compare the torque and angle of rotation at fracture between new and used instruments. The relationship between torque at fracture and size of instrument was determined with a regression analysis. The used instruments had significantly lower torque and angle of rotation at fracture values compared with the new instruments (p < 0.0001). A stronger relationship was found between the size of the instrument and the torque at fracture for the new instruments (p < 0.0001) than for the used ones (p < 0.0001). In conclusion, the repeated use of.06 ProFile instruments significantly reduced the torque and angle of rotation at fracture.