thanks to aidan…
from the web…
Can any one tell me why we get like electric shocks or whatever
when we chew on a piece of aluminum foil (with silver fillings in a couple of teeth)?
That is exactly what you get…an electric shock. The filling is
made of an amalgam of mercury and either tin or silver. When the aluminum foil touches the filling, a galvanic cell is created in the mouth.
Aluminum is the anode, the filling is the cathode and the saliva is the electrolyte ‘salt bridge.’ The contact essentially short circuits the cell and a small amount of current flows which is sensed by the nerves in the teeth. There is the pain you feel.