Why does touching tinfoil with your teeth, especially when you have fillings, hurt so much?

Question

Why does touching tinfoil with your teeth, especially when you have fillings, hurt so much?

In: Other

Answer 1

You create a galvanic cell in your mouth.

The filling in your teeth (mercury alloy) and the tinfoil (aluminium) are the two electrodes, and the saliva (pH range 6.2-7.6) is the electrolyte running the redox reaction.

In short, you have a battery in your mouth.