Effect of sterilization on the cutting efficiency of rotary nickel-titanium endodontic files

Objective. Nickel-titanium instruments that offer greater flexibility than instruments made of other metallic materials have been developed. This study evaluated the behavior in vitro of nickel-titanium rotary instruments under repeated sterilization cycles. Study Design. To investigate changes in cutting ability and superficial alterations, 36 ProFile instruments, 18 with a taper of .04 and 18 with a taper of .06, were exposed to different sterilization cycles. Samples were divided into 3 groups of 12 files each. The 12 group A samples were exposed to 14 cycles of sterilization for 30 minutes; the 12 group B samples were exposed to 7 cycles of sterilization for 30 minutes; the 12 group C samples were not sterilized and served as a control group. Chemical compositions of the near surface layers of samples of each group were determined by means of Auger spectroscopy. Results. The instruments that underwent the greatest number of sterilizations (group A) showed in-depth distributions of chemical composition that were different from those seen in the control group; this was the result of greater amounts of titanium oxide on the surfaces of the sterilized instruments. The files of group A showed a decrease in cutting efficiency in comparison with those of the control group. Conclusions. On the basis of this research on nickel-titanium files, we determined that repeated sterilizations under autoclave alter the superficial structure of such instruments. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:343-7)