Research on corrosion fatigue of dental metals

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Since corrosion and fatigue relate each other complexly in corrosion fatigue phenomenon, these factors should be investigated thoroughly.In this research project, the deformation behavior of cast dental metals was examined by a dynamic hardness tester prior to the fatigue test. As a result, titanium formed by hexagonal closed pack structure showed a different deformation behavior from usual dental alloys formed by face centered cubic structure.Secondly, a long-term immersion test for released ion detection and bimetallic corrosion test were carried out to investigate the corrosion behavior of dental metals. From the base metals whose corrosion resistance are kept by passivation like titanium, the amount of released ions was proved to increase slightly in contact with a nobler metal.With respect to the factor of specimen size, it is prove to be more influential in the mechanical property of cast titanium than in cobalt-chromium alloy. As for the influence of surface condition on fatigue property, the fatigue strength of polished specimen is considerably higher than that of as cast specimen. Taking account of human chewing cycle, the cycle of the fatigue test was estimated about 2 Hz. In the fatigue test in the air, the acceleration up to 10 Hz is proved to cause no difference. However, since the corrosion fatigue property affected much by the time factor, the test condition was set at 2Hz. From the result, dental prostheses should be designed to reduce the stress lower then 160 MPa in titanium castings and 200 MPa in cobalt-chromium castings for ten-year use at a chewing rate of 2000 times per day.