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. Meth ods. The novel approach relies on the cold welding of surface-treated silver particles. At ambient temperatures, intermetallic compound form ation takes place spontaneously al the silver-tin interface. The abili ty of a loose powder to consolidate at ambient temperature under moder ate pressure and within a short time duration was investigated for var ious mixtures of elemental silver, tin, and pre-alloyed silver-coated powders. Surface treatment aimed at removing silver surface oxide laye rs is done with a dilute acid. The compressive and the transverse rupt ure strengths of several of the consolidated powder mixtures were dete rmined. Results. Cold-welding of surface-treated powder particles take s place across the silver-silver interface and is promoted by exposure to a mild acid. Powder mixtures containing approximately 50% silver p owder, 40% silver-coated silver-tin intermetallic compound particles, and a small silver-tin fraction deposited from an aqueous solution dis play very good condensability, depending on the amount of silver-silve r interface area available. The attained rupture strength values (200 Mpa) were higher than those of amalgams; the compressive strengths (12 0 MPa) and hardness values (100 KHN), however, were lower than those f ound for amalgams. Significance. Mercury-free silver-tin powder mixtur es can be processed for use as metallic composite dental restorative m aterials.