Abstract:

[Abstract] 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. Microstructure 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 decreased 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.

Key words: stainless steel, steam, sterilization, root canal therapy, dental instruments, dental instruments