Question

Why is it that when one of my older silver tooth fillings comes into contact with metal stuck on food such as a gum wrapper or aluminium foil, I get intense pain? My guess is that the different types of metal in saliva create a small electrical current. If so, how does this happen?

Answer 1

One of the things that could certainly be happening when you touch two metals together in your mouth, where there's a load of electrolytes, is you've essentially made a battery. If you have two metals of different reactivities, the most reactive one will tend to form ions. So if you've got aluminium foil, that's quite a reactive metal. That will form Al³⁺ ions that will dissolve in your saliva, which acts as the electrolyte. In the process, the less reactive metal will have a load of extra electrons given to it and it will have to somehow get rid of those electrons.

So, if there are any dissolved things nearby, salt metals for example, they will deposit on the surface. Alternatively, there could be some other electrochemistry going on. My guess as to what's going on in your filling is that some of that electrochemistry is happening near the nerve in your tooth and it