Scientific and Industrial Complex “Supermetal” JSC, Moscow, Russia

D. S. Tykochinskiy, Leading Researcher, e-mail: Tykochin@yandex.ru
V. V. Vasekin, Chief Executive Officer

G. S. Stepanova, Deputy Head of Department

The purpose of this investigation was to create a new yellow gold alloy for the casting of metal-ceramic dentures' frames. The yellow color corresponds to the consumer and aesthetic needs of some patients, because of the sign of noble and innocuous metal. At the same time, it is necessary to ensure the correspondence of the alloy properties with the properties of the ceramics, applied on the metal frame. For this purpose, the thermal expansion coefficient of the alloy (TEC) should be in the range of (13.5–14.5) · 10^-6 K^-1, with the heating from 20 °C to 600 °C. Platinum and palladium are the main alloying elements of the majority of gold alloys for metal-ceramics. These metals increase the characteristics of strength. Copper, tin, and other precious and base metals are also included in these alloys. Alloying of gold with platinum and palladium in the two-component alloys, leads to the decrease in the TEC. However, TEC increases with introduction of copper, silver, and tin. The multidirectional influence of the alloying elements is the achievement factor in the compliance of TEC with the given values of the alloy. However, in multicomponent systems, the mutual influence of individual components on the alloy properties is unpredictable. This also applies to the color characteristics of the alloys, which vary in the direction of yellowness reduction with the increasing of platinum and palladium concentration, while other elements may have the opposite effect on the results. The yellowness index (YI), calculated according to the results of spectrophotometric studies, was chosen as an objective indicator of color. In this study, the requirement for YI was given as not less than 25. The color of such alloys can be called light yellow. All investigated alloys contain 85% (wt.) of gold. Therefore, the higher corrosion resistance and biological inertness of finished dental products were ensured. Two the “most yellow” alloys were selected among the alloys that met the requirements of both yellowness and TEC. The adhesive properties of these alloys met the requirements of the State Standard R 51736-2001 to the alloys for metal ceramics: bond strength with ceramics, applied on the surface of a metal sample, was above a minimum value, equal to 25 MPa (Table 2).

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