Wear resistance of cryogenically treated stainless steel files.

Cryogenic treatment, which involves ultra-sub-zero treatment of metal alloys, has been shown to improve the wear resistance of several types of stainless steel. The purpose of this study was to examine the effect of cryogenic treatment on wear resistance of Flex-R and Hedstrom (Union Broach) files. These instruments were attached to an Instron testing machine and underwent 300 push-pull strokes (6-mm movement range, 600-mm/min speed, 1-N loading) against 1.5-mm thick dentin wafers. Their wear was determined by comparing the depth of grooves (without changing file position) cut in acrylic specimens (1.5-mm thick) before and after machining dentin. The mean and standard deviation (n = 20) of the relative change in cutting efficiency was determined for the files. An analysis of variance showed that the cutting efficiency of all files decreased significantly after wearing on dentin (p < 0.0001). However, when comparing the post-/pre-cutting efficiency ratios of the files, it was seen that cryogenic treatment did not affect the wear resistance of the files.