Science Questions

Why does foil touching a tooth filling taste strange?

Sun, 8th Feb 2009

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Question

Daniel Migneault asked:

Why does foil touching a tooth filling taste strange?

Answer

Chris - Did you ever do the thing when you were at school where you put your metal pencil sharpener in your mouth?

Helen - Iíve never tried!

Chris - Certain pens that have a clip that you put over your pocket and itís made of metal, a different metal to the pen. You suck those and occasionally you notice a tingly sensation in your mouth. Have you ever noticed that?

Helen - Iím going to try now but my penĎs plastic.

Chris - That wonít work. The point is that when you mix two different metals together and you have an electrical conductor between them and you have an electrolyte Ė saliva has lots of salt in it so itís an excellent conductor. You can get a chemical reaction happening between the two metals. One metal, the more reactive on will form ions and it will give up electrons which will flow through the electrolytes to the less reactive metals. Thatís how ht e reaction occurs. As a result if you tough two metals, in this case youíre touching with a filling Ė thatís mercury-silver amalgam Ė the aluminium will dissolve to make some aluminium ions. Itíll make some electrical current which you will experience in your mouth as this tingling sensation and it will also react with the saliva to produce some hydrogen and some oxygen gas perhaps on the two different surfaces. You will actually deposit some material on your filling. Youíre basically turning your mouth into a battery.

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Daniel Migneault asked the Naked Scientists: Hi, We would like to know what causes the weird sensation we get when we (accidentally, we assure you) get foil in our mouth and it touches our tooth fillings. Thanks for your help, Julie and Daniel Gatineau, Canada What do you think? Daniel Migneault , Wed, 4th Feb 2009

A little current passes through your tooth nerve, because of Volta Effect:
http://en.wikipedia.org/wiki/Volta_potential
http://ppp.unipv.it/Collana/Pages/Libri/Saggi/Nuova%20Voltiana3_PDF/cap5/5new.pdf

The current in the nerve is perceived as displeasing/pain. lightarrow, Wed, 4th Feb 2009

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