Amalgamation
According to the 
Concise Oxford Dictionary, an 
amalgamation is a derivative of the word 
amalgamate, meaning
-  To combine or unite into one form, or
-  In Chemistry, this denotes a metallic alloy with the element mercury, often used in tooth fillings.
 
Thus an 
amalgamation is a combination of things, or a mercuric alloy.
The use of mercury amalgams in tooth fillings is subject to some controversy, due to suspicions poisonous mercury could "leak."  
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