RESUMEN
Objective Comparing the effects of steam sterilization on cyclic fatigue of stainless steel files. Meth-ods Fifty instruments of 25# stainless steel K files were randomly divided into 5 groups, which include 10 in each group. Group 1 was the blank control group, group 2 to 5 were subjected to 1, 3, 4, 5 steam sterilization cycles, then the files were tested by a custom-made device to assess cyclic fatigue and the number of cycles of failure (NCF) was calculated. Microstruc-ture of each file’s fracture surface was analyzed by Scanning Electron microscope (SEM). Results NCF in the 5 groups were 4 345.2 ± 384.2,3 937.9 ± 645.4,3 812.9 ± 532.5,3 626.2 ± 380.0,3 625.9 ± 565.6 respectively, and the differences among 5 groups were significantly different(F=2.598, P<0.05). After 4 or 5 times of steam sterilization, cyclic fatigue de-creased if compared with that in control group (P<0.05). Fracture surface in group 1 and group 2 was tough dimple structure and large numbers of regular, deep dimples were distributed on the surface. You could also see micro cavities clearly formed by fracture;Fracture surface in group 4 was dimple structure in brittle intergranular morphology. It is characterized by the presence of thin brittle precipitates, clean and smooth crystal interface, and a great sense of polyhedral stereo. Conclusion After 4 times of steam sterilization, cyclic fatigue strength of 25# stainless steel K files declined, which possessed the poten-tial risk of fracture.