The purpose of the following experiment is to examine the relation between changes of dental casting alloys in vivo and results of immersion tests. Five kinds of dental casting alloys were implanted into dorsal subcutaneous tissues of Wistar rats. The histological reactions of the local tissues surrounding implanted alloys were investigated after each period of 1, 3 and 6 months. Also, SEM-observation of surface changes, EPMA-analysis of chemical composition and weight measurement for 6-month

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... riod were performed. The results are as follows. 1) Gold alloy and Ag-Pd-Cu-Au alloy showed slight tissue reactions and very few changes in weight, surface and composition. 2) Tissue reactions of Ag-Sn-Zn alloy were as moderate as those of low-chromium Ni-Cr (86 Ni-10Cr) alloy. Though it showed a few weight changes, the obvious changes of surface and composition were similar to the result of 1% lactic acid. 3) Low-chromium Ni-Cr(86 Ni-10 Cr) alloy showed slight loss in weight and few changes in surface and composition in vivo, that was similar to the result of Ringer's solution. 4) High-chromium Ni-Cr(70 Ni-19 Cr) alloy showed severe tissue reactions as compared with those of other alloys. A little weight loss was observed only after 6 months. Changes in surface and composition were similar to the result of 0.05% HCl.