title: A new technology for direct restorative alloys.
abstract: OBJECTIVE
  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 temperature, 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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  Mercury-free silver-tin powder mixtures can be processed for use as metallic composite dental restorative materials.
authors.affiliation: National Institutes of Standards and Technology, Gaithersburg, Maryland, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Dariel
authors.forename: D S
authors.initials: DS
authors.lastname: Lashmore
authors.forename: M
authors.initials: M
authors.lastname: Ratzker
mesh_terms: D000704:Analysis of Variance; D001881:Borates; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003722:Dental Alloys / Q000737:chemistry*; D003793:Dental Restoration, Permanent / Q000379:methods; D012994:Dental Soldering / Q000379:methods*; D004339:Drug Compounding; D004572:Electrolysis; D006244:Hardness; D008422:Materials Testing; D008669:Metallurgy / Q000379:methods; D011312:Pressure; D012834:Silver / Q000737:chemistry; D013499:Surface Properties; D014001:Tin / Q000737:chemistry; D014896:Welding / Q000379:methods; D014961:X-Ray Diffraction
chemical_list: D001881:Borates; D003722:Dental Alloys; D012834:Silver; D014001:Tin; C098759:fluoroboric acid