title: Factors affecting the optical properties of Pd-free Au-Pt-based dental alloys.
abstract: The optical properties of experimental Au-Pt-based alloys containing a small amount of In, Sn, and Zn were investigated by spectrophotometric colorimetry to extract factors affecting color of Au-Pt-based high-karat dental alloys. It was found that the optical properties of Au-Pt-based alloys are strongly affected by the number of valence electrons per atom in an alloy, namely, the electron:atom ratio, e/a. That is, by increasing the e/a-value, activities of reflection in the long-wavelength range and absorption in the short-wavelength range in the visible spectrum apparently increased. As a result, the maximum slope of the spectral reflectance curve at the absorption edge, which is located near 515 nm (approximately 2.4 eV), apparently increased with e/a-value. Due to this effect, the b*-coordinate (yellow-blue) in the CIELAB color space considerably increased and the a*-coordinate (red-green) slightly increased with e/a-value. The addition of a third element with a higher number of valence electrons to the binary Au-Pt alloy is, therefore, effective in giving a gold tinge to the parent Au-Pt alloy. This information may be useful in controlling the color of Au-Pt-based dental alloys.
authors.affiliation: Division of Dental and Biomedical Materials Science, Department of Developmental and Reconstructive Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan. siraisi@net.nagasaki-u.ac.jp
authors.forename: Takanobu
authors.initials: T
authors.lastname: Shiraishi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Takuma
authors.forename: Eri
authors.initials: E
authors.lastname: Miura
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Hisatsune