What is that weird feeling I get when I place a metal spoon on my teeth?
• That feeling could be down to a galvanic effect, in which your mouth acts like a battery. If you have metal tooth fillings made of gold alloys or of mercury amalgam, then a spoon can create an electrochemical cell.
It is like a simple battery cell consisting of two different metals (electrodes) in a suitable medium (electrolyte). In the mouth, saliva could act as the electrolyte.
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A current of a few microamps may result, which can produce a distinctive taste or tingling in the mouth. The effect size depends on the metals and, presumably, the nature of your saliva, so some people feel the effect more.
There are reports of people with several fillings of different metals who claim to experience a prolonged bad taste, burning sensation or pain from a galvanic current, no spoon required.
Richard Swifte
Darmstadt, Germany
• To test whether the galvanic effect is responsible for what you feel, take a bit of aluminium foil and bite on it gently. First keep it away from fillings to see whether you get that feeling, then chew it – still gently – where a filling is. If you only get the feeling when a filling touches the aluminium, then galvanic shock is the source. If not, it might be the sensation of your tooth touching something hard. Some people find such contact intensely unpleasant.
Jon Richfield
Somerset West, South Africa
• It isn’t just teeth. Galvanic currents played havoc with early British warships in the mid-to-late 1700s, when wooden hulls were clad with copper sheets to protect them from damage by the teredo worm. HMS Alarm was the first to be clad. The worm was defeated, but the ship’s iron fittings, including bolts in the hull, quickly corroded due to electrochemical effects between the two metals.
Lewis Perdue
Sonoma, California
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