A silver-tin alternative to dental amalgams
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M. Ratzker, A. Giuseppetti, and F. C. Eichmiller American Dental Association Health Foundation, Paffenbarger Research Center, NIST, Gaithersburg, Maryland 20899 (Received 3 August 1994; accepted 21 October 1994)
This paper describes a novel technology for a mercury-free metallic direct filling material, a substitute to dental amalgams. The consolidation relies both on cold-welding that takes place under moderate pressure between suitably surface-treated silver particles and on silver-tin intermetallic compound formation at ambient temperature. A dilute acid is used for removing the silver surface oxide layers, thereby promoting the cold-welding process. The condensability, namely the ability of a loose powder to undergo consolidation within a short time duration, at body temperature and under moderate pressure has been investigated for a variety of mixtures of silver, tin, and prealloyed silver-coated intermetallic powders. The resulting metallic composite material displays transverse rupture strength values higher than those of amalgams and somewhat lower values of compressive strength and Knoop hardness. I. INTRODUCTION
Of the overall amount of mercury that results from various human activities and is discharged in the environment, only a minute fraction can be attributed to its use in dentistry. Waste from dental clinics, however, makes up a major fraction of the mercury collected in the sludge generated in water-purifying plants. Mercury is considered to be a dangerous environmental pollutant. In aquatic environments, for example, biological magnification factors of up to 100,000 from algae to large fish level have been reported. The increasing public awareness of the risks involved in the accumulation of mercury in waste has led to the restriction of its use and to mandatory installation of mercury-separating apparatus in dental clinics in several European countries. Dental amalgams have been in continuing use for over a century. Their widespread and lengthy service is due to a favorable combination of properties that meet the requirements for a dental restorative material. These properties include adequate mechanical strength, wear resistance, corrosion resistance in an oral environment, dimensional stability, biocompatibility, and ease of placement.1 The ease of placement of a dental amalgam is facilitated through the material's capacity to undergo transformation from a plastic and malleable material to a rigid, cohesive solid at body temperature. Mercury by mixing with prealloyed silver-tin-copper compound powders forms a malleable plastic mass. A liquid phase
a) On
leave from the Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel. b) Presently with Materials Innovation, Lebanon, New Hampshire 03784. J. Mater. Res., Vol. 10, No. 3, Mar 1995
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diffusion reaction takes place between mercury and the solid component to yield a cohesive mass consisting of some of the initial prealloyed compounds embedded in the ne
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