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PRINCIPLES OF DEVELOPMENT OF DENTAL NOBLE METAL ALLOYS
TYKOCHINSKY D.S., VASEKIN V.V., LEVCHENKO S.D.
FSUE SIC "Supermetal", Moscow, Russia
Annotation. The results of the study in the field of the effect of alloying elements on the properties of gold alloys, which was carried out at "Supermetal" with the purpose of development of new alloys for dentures, have been presented in the report. All designed and produced alloys have a high content of noble metals (the total of gold and platinoids is 70 to 98 % by mass); they have a high corrosion resistance and biological inertness and satisfy the medical and technical requirements.
Keywords: alloy, dentistry, noble metal, gold, alloying element, properties.
In addition to the basic products (platinum accessories for silicate production), "Supermetal" produces dental alloys on the base of noble metals and continues to develop new alloys for prosthetic dentistry in cooperation with the Moscow State University of Medicine and Dentistry. Proceeding from the dentists’ and patients’ practical requests, the University defines the purpose of the alloys. The major dental alloy producers’ experience has been taken into account.
The ideology of development of our dental materials on the base of noble metals is based on a principle of optimum functional properties in combination with obligatory medical and technical compliance:
· toxicological inertness and biocompatibility with the tissues of the oral cavity;
· corrosion resistance;
· conformity of mechanical characteristics to requirements of the international standards;
· processibility in conditions of dental laboratories;
· correspondence between the coefficient of thermal expansion of the alloy and that of the ceramics used to cover it (requirement for the alloys for cermet designs);
· Aesthetic characteristics.
A high corrosion resistance of Supermetal alloys in artificial saliva and other acid or alkaline solutions results from a high content of noble metals (the total of gold and platinoids is 70 to 98 %). The alloys are biologically inert; they do not contain any toxic or allergic alloying elements (Cd, Ni, Be).
Gold and palladium are the base of Supermetal dental alloys. In addition to high chemical and biological inertness, these noble metals are able to form alloys with structures of solid solutions, with many alloying elements, noble or ignoble (Pt, Ag, Cu, Zn, for example). Scientifically substantiated selection of alloying elements and their concentrations enables to control the strength and processing characteristics of the alloys. In particular, the alloys of gold with copper and silver can be strengthened by heat treatment; and alloying with platinoids improves the strength of the gold alloys.
Alloying elements can have an influence on the coefficient of thermal expansion in different ways. Some from them improve this parameter, while the others do not. Experiments have enabled to choose the best concentration of the elements when developing the alloys for dental ceramics.
All the alloys on the base of palladium are practically white (colorless). The alloying of gold alloys with platinoids results in suppression of yellow color; therefore, alloys with 15 to 17 % Pt+Pd grow white even with the content of gold of 80 % and higher. On the contrary, when alloying with silver and copper, the alloys with a low or zero content of platinoids can have more or less expressed gold color, down to 65 to 70 % of gold. Taking into account a substantial demand for yellow alloys, "Supermetal" has used the results of spectrophotometric investigation of colorimetric parameters of gold alloys. The choice of concentration of alloying elements depended on their effect on the coefficient of yellowness.
All the alloys, designed at "Supermetal", have passed clinical tests and are approved by the Ministry of Health of Russia.