Development of Dental Alloys alternative to Ag-Pd-Cu-Au Alloys

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Experimental Pd-free Ag-Au-Pt-Cu alloys with various chemical compositions were prepared to substitute for traditional dental Ag-Pd-Cu-Au alloys. Liquidus and solidus temperatures were determined from DSC data. Spectrophotometric colorimetry was performed to investigate the optical properties and to quantify the tarnish resistance in the 0.1% Na_2S solution. Principal results obtained are as follows.1. In the alloys with the same Au content, both liquidus and solidus temperatures lowered with increasing Cu content. Solidification temperature range became narrow with increasing Cu content.2. In all the experimental alloys, spectral reflectance was high in the long-wavelength region and very low in the short-wavelength region due to the effective absorption of light.3. In the alloys with the same Cu content, the absorption edge systematically moved towards longer wavelength direction with increasing Au content. Simultaneously, spectral reflectance in the long-wavelength region slightly decreased with increasing Au content. Owing to these systematic variations of spectral reflectance curves, chromaticity index b^* (yellow-blue) apparently increased, giving a gold tinge to the alloy.4. In the alloys with the same Cu content of 15 at.% or 20 at.%, tarnish resistance of the alloys in the 0.1% Na_2S solution was markedly improved with Au content.5. Among the three coordinates, L^*, a^*, b^*, in the CIELAB color space, decrease in L^*-value effectively affected the color change, ΔE^*, of the material in the tarnish test solution.