Torsional properties of stainless-steel and nickel-titanium files after multiple autoclave sterilizations

This study tested the hypothesis that multiple sterilizations of endodontic stainless-steel and nickel-titanium files wilt lead to a continuous decrea se in the resistance of files to separation by torsion. One hundred stainle ss-steel and 100 nickel-titanium #30 K-type files were divided into 20 grou ps of 10 and sterilized in increments of 10 cycles, using a full cycle and a fast cycle autoclave, These files were tested by twisting each of them in a clockwise direction until fracture (torque g-cm), Samples of the fractur ed flies were embedded in an epoxy resin and polished for Knoop hardness te sts. In addition, the samples were chemically etched to reveal changes in m icrostructure, The findings of this study indicate that neither the number of sterilization cycles nor the type of autoclave sterilization used affect s the torsional properties, hardness, and microstructure of stainless-steel and nickel-titanium files.