Research on corrosion fatigue of dental metals

在腐蚀疲劳现象中，腐蚀和疲劳之间有着复杂的联系，因此需要对腐蚀和疲劳的影响因素进行深入的研究。结果表明，六方封闭堆积结构形成的钛表现出不同于通常的面心立方结构形成的牙科合金的变形行为。其次，为了研究牙科金属的腐蚀行为，进行了长期浸泡释放离子检测试验和双金属腐蚀试验。在钛等耐蚀性较好的母材中，与贵金属接触时，离子的释放量略有增加，试件尺寸对铸钛力学性能的影响大于钴铬合金。就表面状态对疲劳性能的影响而言，抛光试件的疲劳强度明显高于铸态试件。考虑到人体的咀嚼周期，疲劳试验的周期估计为2赫兹左右。在空气中的疲劳试验证明，高达10赫兹的加速度没有引起任何差异。然而，由于腐蚀疲劳性能受时间因素的影响较大，因此将试验条件设置为2赫兹。结果表明，钛铸件的牙体应力应低于160 Mpa，钴铬铸件的应力应低于200 Mpa，以每天2000次的咀嚼速度使用10年。

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.