Abstract
The clasp arms are fatigued by wearing a denture, by taking it off, and by occlusion. We routinely use laser irradiation to harden only the surface layer of clasp arms consisting of gold-silver-palladium alloy partially hardened by laser irradiation to resist fatigue. Recently we tested laser irradiation on silver-palladium-copper alloys, and obtained the following results: 1) The surface hardness of the mother alloy No. 12 (52.5Ag−12.5Pd−35.0Cu alloy (wt%)) was 299.7HV after laser irradiation, 155% harder than after casting. 2) The surface hardness of the 18Au−40Ag−20Pd−22Cu alloy (wt%) was 235.0HV after laser irradiation, 91% harder than after being softened, 15% harder than that after being hardened. The brightness (L*) of the specimens immersed in 0.1% sodium sulfide solution at 37°C for 3 days was 73.07. 3) The surface hardness of the 12Au−40Ag−20Pd−24Cu−4Zn alloy (wt %) was 270.0HV after laser irradiation, 165% harder than after being softened, and 78% harder than that after being hardened.
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