I have never tried the specific product "Opalescence".  I have used a lot of
Nupro bleaching chemistry and Patterson brand.  Neither one has ever caused
any amalgam discoloration that I have seen or been told of.

I was thinking it was probably a manganese compound.  I don't know
whether there is/was Mn in amalgam.  The bleach makers seem remarkably
incurious: "It has been theorized that the zinc in old amalgams may be
the cause of the discoloration."  How hard is it to get some old
fillings together with an analytical chemist and an atomic absorption
machine?  So I doubt the claim that the Opalescence is harmless to fillings.

I am trying to think of what oxidation reaction will result in a purple
color.  I need help from someone more recent on chemical reactions.  Cu
would turn green (with a slight bluish tint),  What would add red to create
purple?  Mg?  Cannot remember for the life of me.

Anyway, any reaction on the surface of amalgam from a oxidizer like H2O2
should vary by the degree of polish/oxidation on the amalgam and by the
mineral content of the particular alloy.

Could the purple color simply be a gelling agent of flavoring agent in the
bleaching product?

Hmmm ... I thought it was common knowledge ...

Maybe I erred---maybe it only happens with carbamide peroxide and older
amalgam:

http://www.ultradent.com/products/products.php?act=faq&fid=1&pid=4#45

Why does OPALESCENCE change to a dark purple/black color when it comes
in contact with amalgam?
The dark purple coloration that may appear in the tray following
bleaching adjacent to older amalgams is normal and has proven
inconsequential, based on years of clinical use. No adverse/detrimental
effect on the amalgam restorations has been experienced. It has been
theorized that the zinc in old amalgams may be the cause of the
discoloration.

http://www1.umn.edu/dental/courses/dent_6806fall02/paper9/paper9.html

Occasionally a slight purple coloration may appear in the tray following
bleaching adjacent to amalgam fillings.

I have done lots of bleaching in my day.  I still have the old Almore
Monarch II bleaching instrument from the days of using superoxol heated with
this device.  [Want to buy it?  :-) ]   Many vital and non-vital bleaching
cases.  Even more cases done with custom fitted trays and take home
chemistry.  I have never seen amalgam discolor from it.

You have never seen a purple reaction product when peroxide touches
fillings?

Maybe there isn't much of an effect from whitestrips since they are OTC
and used only in the front anyway.

I have never noticed that effect.

I believe that hydrogen peroxide corrodes amalgam fillings.

Hi,

   Can anyone shed some light on Crest Whitestrips, where the
active ingredient is Hydrogen Peroxide; Is it harmful/unhealthy on
the teeth?

Thanks.