Re: Why is mercury used in making dental amalgam for fillings?

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