A new technology for direct restorative alloys

Objectives. The purpose of this study was to develop a new technology for preparing mercury-free metallic dental restorative materials. Methods. The novel approach relies on the cold welding of surface-treated silver particles. At ambient temperatures, intermetallic compound formation takes place spontaneously at the silver-tin interface. The ability of a loose powder to consolidate at ambient temperature under moderate pressure and within a short time duration was investigated for various mixtures of elemental silver, tin, and pre-alloyed silver-coated powders. Surface treatment aimed at removing silver surface oxide layers is done with a dilute acid. The compressive and the transverse rupture strengths of several of the consolidated powder mixtures were determined. Cold-welding of surface-treated powder particles takes place across the silver-silver interface and is promoted by exposure to a mild acid. Powder mixtures containing approximately 50% silver powder, 40% silver-coated silver-tin intermetallic compound particles, and a small silver-tin fraction deposited from an aqueous solution display very good condensability, depending on the amount of silver-silver interface area available. The attained rupture strength values (200 Mpa) were higher than those of amalgams; the compressive strengths (120 MPa) and hardness values (100 KHN), however, were lower than those found for amalgams. Mercury-free silver-tin powder mixtures can be processed for use as metallic composite dental restorative materials.