Why can biting on aluminum foil be painful?

When (dental) metal in your mouth comes in contact with aluminum foil, your teeth get a painful shock from the electricity produced. Marshall Brain explains how the voltaic effect plays out in your mouth in this episode.

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Episode Transcript

Speaker 1 (00:00):
Welcome to Brainstuff from house stuff works dot com where
smart Happens. Hi Am Marshall Brain with today's question, why
is it that biting on aluminum foil can be painful?
Biting on aluminum foil can be painful, and it's usually

(00:23):
noticed if you have metal in your mouth from things
like fillings or crowns. Basically, when you bite on foil,
you set up a battery in your mouth and the
electrical current stimulates nerve endings in your tooth that generates pain. Specifically,
here's what happens. First of all, the pressure from biting

(00:43):
brings two different metals, in this case aluminum foil and
mercury in your fillings or gold in your crowns, in
contact with each other in a moist salty environment. The
salty environment is provided by your saliva. The two metals
have an electric chemical potential difference between them, or a
voltage that gets generated because they're coming into contact with

(01:06):
each other. The electrons flow from the foil into the tooth,
so you have this electrical current created by this little
battery flowing into your tooth. The current gets conducted into
the tooth's root, usually by the filling or crown, and
the current sets off nerve impulses in the roots nerve.
Those nerve impulses go to your brain, and then finally,

(01:28):
the brain interprets those impulses as pain. The production of
the electric current between two dissimilar metals like this is
called the Voltaic effect after Alessandro Volta, who discovered it
long ago when he was creating early batteries. He made
them by stacking dissimilar metal discs with blotterer paper soaked

(01:50):
in salt water between them. This was called a voltaic pile,
and it was an easy way to create a simple
and very low power battery. If you have no metal
dental work in your mouth, you're not going to feel
this effect. You've got to have these two dissimilar metals
coming together for you to feel the pain that aluminum
foil causes. Be sure to check out our new video podcast,

(02:15):
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