A comparison of stainless steel and nickel-titanium H-type instruments of identical design:: Torsional and bending tests

Objective. For a true comparison of clinically relevant qualities at instruments manufactured from different alloys, the instrument must be identical in design. The purpose of this study was Co perform mechanical tests on stainless steel and nickel-titanium instruments of identical design. Study design. Identical experimental endodontic files of H-type with double helix were fabricated from stainless steel and nickel-titanium alloys. Torsional and bending tests were carried out according to American National Standards Institute/American Dental Association specification No. 58 and International Standards Organization No. 3630/1. Changes in instruments during the testing were also analyzed with scanning electron microscope technique. Results. The results indicated that the torsional moment of the stainless steel files was significantly higher than for the nickel-titanium files (P < .001), whereas the mean angular deflection for the nickel-titanium files was significantly higher. The mean bending moment for the nickel-titanium flies was significantly lower (P < 001) than the mean value for the stainless steel files. The scanning electron microscope demonstrated that the fracture surfaces of the stainless steel files were brittle, whereas the nickel-titanium files had a ductile fracture. Conclusions. When the design of endodontic instruments of different alloys is identical, the nickel-titanium files are more flexible in bending. However, nickel-titanium files require less force to deform to fracture.