CYCLIC FATIGUE OF THE SODIUM HYPOCHLORITE TREATED AND /OR STEAM AUTOCLAVED NICKEL-TITANIUM ENDODONTIC FILES

The purpose of this study was to determine the effect of sodium hypochlorite and steam autoclaving on the cyclic fatigue of nickel-titanium endodontic files. Two types of files with a .06 taper and #30 were used, (SybronEndo, Glendora, California, USA) and Hero (Micro-Mega, BesanCon, France). The files were divided into 6 experimental groups containing 10 files each group depending the soaking time in 6% sodium hypochlorite solution and number of cycles of steam autoclave. After sterilization, a cyclic fatigue test was performed on each file, and the fracture time was recorded in seconds. The control group underwent the cyclic fatigue test only. After the test, the surface characteristics of the files were observed using scanning electron microscopy (SEM). All groups containing the Hero 64~ files showed a similar cyclic fatigue fracture time. However, the cyclic fatigue fracture time with the files was significantly shorter in groups which were treated with sodium hypochlorite than in the control group (P and files to have significant corrosion on the file surface in groups treated with sodium hypochlorite, compared with the sharp and regular blades of the control group. files showed more corrosion than the Hero files. Bluntness of the blades of the file was observed in groups treated with steam autoclave. Although there was no obvious destruction on the surface of steam autoclaved Hero files, slight bluntness was observed. Sterilizing with a steam autoclave is much less destructive to files than sodium hypochlorite. The longer time exposed to sodium hypochlorite, the more destructive pattern was shown on the blades of the files. Therefore, when using sodium hypochlorite solution, the exposure time should be as short as possible in order to prevent corrosion and increase the cyclic fatigue fracture time.