Optical properties of Au−Pt−Pd-based high noble dental alloys

Abstract

of Au-Pt-Pd-based high noble dental alloys. That is, by increasing e/a-value, a*-, b*-, C*-coordinates systematically increased, giving a slight gold tinge to the parent Au-Pt-Pd alloy within the limitation that the structure of an alloy is a single phase. The addition of Sn of 2 mass % or more produced a small amount of the second phase of possible intermetallic compounds between Sn and Pd or Pt. The coexistence of a small amount of the second phase of possible intermetallic compounds further increased a gold tinge. However, the inclusion of 4 mass % Sn to the parent Au-Pt-Pd alloy gave a very light tint of red to the alloy. Results of the present study are expected to be useful in controlling colour of Au-Pt-Pd-based high noble dental alloys. KeywordsGold alloy, dental alloy, colour, spectral reflectance, spectrophotometric colourimetry, chromaticity index IntroductionThe use of porcelain-fused-to-metal (PFM) dental restorations has achieved widespread acceptance, and several high nobility alloys are available for this specific application (1). Among various types of alloys for PFM restorations, the Au-PtPd-based high noble alloys have the advantage of having been around for some considerable time and clinical experience has shown that they are extremely successful (2). In particular, the bond between the ceramic and the metal is very strong and highly reliable (2). Concerning the formulations of these Au-Pt-Pd-based high noble alloys for porcelain bonding, high Au contents are required to ensure biocompatibility and large Pt and Pd concentrations are necessary to raise the melting range sufficiently above the porcelain firing temperature to prevent distortion during porcelain application (2, 3). A minimum content of about 5% Pd is recommended to increase the sag resistance (4). Base metals such as In, Sn, Zn are added to form a thin oxide film at the surface of the alloy during the porcelain firing cycle (4). In addition to the extremely successful clinical experience, the attraction of the Au-Pt-Pd-based high noble alloys is with the light-yellow colour (b* typically ranges from 9 to 12) (3). German et al. (5) mentioned that although the primary concerns about cast dental restorations are with biocompatibility and corrosion and tarnish resistance, it would be naïve to discount the strong emotional attachment to selected alloy colours involving gold. According to German (3), it is easier to meet the physical and mechanical property requirements for a ceramo-metal alloy using just the Au-Pdbased alloys. However, these alloys tend to be very light in colour (b* 6-8) and have not been universally accepted in spite of the very attractive properties (3). The whitish colour of these Au-Pd-based PFM alloys is considered to be due to the very high level of Pd content of 35 to 45%. Hence, it is suggested that colour control must be taken into account as one of the criteria in manufacturing dental gold alloys not only for crown and bridge restorations but also for PFM restorations.In the present study, we designed sev...

An estimation of the reflectivity of some monophasic binary gold alloys

“…The decolorizing effect of the addition of other metals, especially Pd and/or Pt, is a result of the flattening of spectral reflectance curves over the visible spectrum, thus decreasing the change in reflectivity across the visible [9]. This is especially so in the case of the various white gold alloys [10,11].…”