If they are adjacent or opposite each other so that they contact there
is a small potential generated.  Occasionally a patient will complain of
sensitivity in this case, and the galvanic action may be responsible for
this.  However, if the amalgam is older, tarnish will usually greatly
mitigate any galvanic effect.  I haven't personally seen this if the
restorations aren't in direct contact.

Steve

No quackery involved.  It is a scientific fact that when two dissimilar
metals come in contact with each other that there is an electrical potential
there.  Outside it is the major cause of "galvanic corrosion", but inside
your mouth and with the relatively oxygen inert materials in fillings, there
probably isn't much corrosion.

They do this a lot in Alaska because the cold weather
sometimes incapacitates the regular car battery so you
just hook up the jumper cables to a cupla molars ....

--
Joel34