[Effects of mechanical stress on cytotoxicity of cobalt-chromium alloys for denture base].

The effects of metal ions and mechanical stress on cells were examined in vitro, to shed light on tissue response to metal prosthesis. Seven commercial base alloy plates, four Co-Cr alloys, one pure Ti, one Ni-Cu-Ga alloy and one Ni-Cr alloy for solder were used. Two kinds of static load, 5 gf/cm2 and 10 gf/cm2, were applied to three kinds of tissue culture cells, L-929, HEp-2 and Gin-1 cells, for 24 hours, and then the cells were incubated for 7 days under normal culture conditions. Cell recovery was evaluated by cell number and protein content. The amount of dissolved metal ions was measured by atomic absorption spectroscopy (Experiment 1). A concomitant study of cell culture with known amounts of Co, Cr, Ni was carried out, and cell recovery was examined (Experiment 2). Atomic absorption spectroscopy showed that dissolution of either Co or Cr from the alloys tested was extremely small. However, the maximum amount of Ni and Cu dissolved from Ni-Cu-Ga alloy and Ni-Cr alloy for solder was over 10 ppm. Ti was not dissolved from pure Ti. Four Co-Cr alloys and pure Ti did not inhibit cell recovery or protein content with loading. However, Ni-Cu-Ga alloy and Ni-Cr alloy significantly inhibited cell recovery and protein content, and the effects were enhanced by loading. The cytotoxicity of Co, Cr or Ni ion at a static load of 10 gf/cm2 was higher than that at 5 gf/cm2. These results suggest that mechanical stress increases the cytotoxicity of dissolved metal ions.