|MadSci Network: Chemistry|
Mercury is used for making dental amalgams because it forms solutions with silver and gold. Silver or gold powder (about 35%) are mixed with tin or tin/copper (about 15%) and mercury (about 50%) to form a mallable paste that can be worked into a cleaned-out cavity. As the solution process continues (it takes a little while for the silver or gold to finish dissolving), the amalgam hardens and assumes a permanent shape. The resulting amalgam has excellent physical properties for making fillings. It has good chemical stability in the acidic environment in the mouth, it adheres well to tooth enamel so it forms good seals around the cavity and can be pressed (while it is still malleable)into very thin margins to taper it to nature tooth contours. In addition, it has high compressive strength so you can clamp your teeth right down on it. Recently, there has been concern that the mercury can leach out of the amalgam over time. This issue is not resolved. There is work on plastic composite materials for fillings including some "photoset" polymers that are hardened by shining a laser on them. They are more attractive since they are white but lack the structureal strength of amalgam Check these sites: www.umds.ac.uk/elsewhere/dental/mercury.html www.cityscape.co.uk/users/ad88/mercury/htm www.towne.com/tol.html
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