A recently developed mercury-free direct filling alloy is under investigation through NIST/NIDR Interagency Agreement NIH-NIDR 3093-4, NIDR CEMSR grant P50-DE09322 to the ADA Health Foundation (ADAHF), and NIST Cooperative Research and Development Agreement (CRADA) with Dentsply Int. A CEMSR pilot project began in 1993 to assess the feasibility of this alloy. Model restorations were fabricated with silver and tin powders and gold-plated silver foils to prove the concepts of cold welding and fast solid-state diffusion. A full project supplemented the grant in 1993-94 to evaluate mixtures of pure metal powders, primarily silver and tin, as an alternative direct filling material. This project and the NIST IA demonstrated the feasibility of a powdered-metal material that can be directly consolidated into a tooth cavity. The material is comprised of silver, tin, and silver-tin alloy spherical powders coated by electrodeposition methods with pure silver or tin and placed in an acidic media to remove surface oxides. With dental instruments the oxide-free mixture is consolidated into the cavity preparation as a liquid/powder paste, welding the individual metal particles together. The initial welding produces a metal with properties similar to and in some cases better than dental amalgam. The material has a much more homogeneous microstructure than amalgam and lower corresponding corrosion potential. Physical property measurements on lab specimens have shown tensile strength higher than amalgam. While this material appears to have very high dental restorative potential, questions remain regarding its clinical use. Most parameters vital to clinical application have yet to be studied. The properties comparative to amalgam such as compressive and tensile strength, hardness, cavity adaptation, and margin microleakage need to be assessed to predict clinical performance and optimal conditions for material placement. A clinical simulation is needed to compare the methods and instrumentation of this system with those of conventional amalgam. This simulation will provide the clinical protocol for future clinical trials and a method to assess the ability of unfamiliar operators to adapt to the new materials and methods. NIST IA responsibility: the engineering and development of the alloy system and biocompatibility testing; the ADAHF responsibility: development of the clinical delivery methods and instrumentation needed to apply this material. This collaborative results will bring this technology to clinical practice quickly and efficiently.
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