Oral Electricity

For some years, I've accused my wife of deliberately trying to cause me pain by inserting in my salami sandwiches the sheet of aluminum foil that sometimes sticks to the last slice in the package. Each time I am awarded by a disdainful laugh and a comment that biting into a little bit of aluminum couldn't possibly hurt anyone who claimed to be tough enough to live in the Frozen North.

Therefore, it was with great glee that I received from University of Alaska geology professor Daniel Hawkins an article he had found explaining why biting aluminum foil hurts so much. The article states that considerable pain or discomfort can result from a tooth filling coming into contact with certain metals.

The standard dental filling is an alloy of silver, tin and mercury. When a piece of aluminum or similar electrically active metal is places in the mouth a wet-cell battery is formed. The tooth fillings form one electrode, the piece of aluminum the other, and the mouth's saliva becomes the electrolyte. By actual measurement with a voltmeter and an aluminum gum wrapper, my mouth battery creates about one-half volt. If the voltmeter probe is touched to different fillings, slightly different voltages result, indicating different amalgams used by the dentists I have patronized over the years.

The sharp pain comes when the mouth battery is short-circuited by touching the aluminum electrode to the dental amalgam electrode. Then a quick surge of current flows. Though the current is relatively weak, it is strong enough to be painfully sensed by the nerves of the teeth. The current quickly stops, so the pain is brief.