Abstract:The Gram-negative anaerobic bacterium Porphyromonas gingivalis is an etiologically important pathogen for chronic periodontal diseases in adults. Our previous study suggested that the major structural components of both Fim and Mfa fimbriae in this organism are secreted through their lipidated precursors. In this study, auto-polymerized to form Fim fimbriae.

The effects of platinum addition to gold and indium addition to a gold-platinum alloy on their optical properties were investigated using a computer-controlled spectrophotometer. Spectral reflectance data from a polished sample for the incident CIE standard illuminant D65 was collected as a function of the wavelength at 10 nm intervals from 360 to 740 nm. Three coordinates, L* (lightness), a* (red-green), b* (yellow-blue), in the CIE 1976 L*a*b* colour space, were determined to quantify the colour of experimental binary Au-Pt and ternary Au-Pt-In alloys.The pronounced step near 520 nm (approximately 2.4 eV) in the spectral reflectance-wavelength curve for pure gold, which is responsible for the rich yellow colour of gold, became less pronounced with the addition of platinum. The decoloring effect of platinum was found to be due to this phenomenon. The addition of indium of up to ca 4 at% to a Au-10 at% Pt alloy increased both chromaticity indices, ie, a* and b* values, giving a gold tinge to the alloy: this effect was brought about by both the slight increase in reflectance in the long-wavelength range and the slight decrease in reflectance in the short-wavelength range of the visible spectrum.

Nine experimental Pd-free Ag-Au-Pt-Cu dental alloys containing 10 at.% Pt and 10 to 35 at.% Au were prepared and their optical properties and microstructures were investigated by means of spectrophotometric colorimetry, optical microscopy, and electron probe microanalysis. All the alloys were annealed at 850°C and mirror-polished to observe their reflectance curves in the visible spectrum and three-dimensional color coordinates. All the alloys were composed of a major phase of Ag-Au-rich matrix and a minor and almost colorless Pt-Cu-rich phase. It was found that the color of the alloys was substantially controlled by the Ag-Au-rich matrix and that with increasing Au/Ag atomic ratio from 0.130 to 0.996, the yellow-blue chromaticity index b* increased from 8.0 to 14.4, giving a pale yellow color. This systematic increase in yellowness was caused by a continuous shift of the absorption edge of reflectance curve towards longer wavelengths with increasing Au/Ag atomic ratio.

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.