Lapis
I too have been wondering the same thing. Here's what I've found so far:
http://www-safety.deas.harvard.edu/ChemIncom.html
Hydrogen peroxide should not be mixed with: Copper, chromium, iron, most metals or their salts, alcohols, acetone, organic materials, aniline, nitromethane, combustible materials.
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http://triballi.mybravenet.com/mercury.html
"It has been shown that mercury is continually released from mercury dental fillings in the form of mercury vapor and abraded particles. This process is further stimulated and can be increased as much as 15-fold by simply chewing, brushing teeth, hot drinks and even swishing your mouth with a solution of hydrogen peroxide (used to reduce dental plaque.)"
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