Why does biting foil hurt my teeth

A.� Biting foil only hurts those of us who have spent more time eating sweets than looking after their teeth and so have fillings. The foil is actually reacting with the metal in your filling.

�

The foil and your filling are separated by a conductive fluid, your saliva, which allows an electrical current to flow between them. This electrical charge irritates the dental nerve in your tooth that the filling is covering and causes the painful sensation you feel.

�

Q.� So it has to be two metallic surfaces

A.� Yes, all metals have different electromotive potentials, which means that when they come into contact with each other this difference results in a weak current to flow between them. The official term for this electric flow is Galvanism.

�

Q.� Why does a current flow between the foil and the filling

A.� This is where things start to get a bit technical.

�

Fillings are made of silver, mercury and tin, which remain stable in the tooth. However aluminium, in the foil, is unstable, and as soon as it comes into contact with the water in your saliva it starts to react, loosing electrons as it does so. These freed up electrons are attracted to the metals in your filling, which produces an electric current of around half a volt.

�

Fortunately the current flow is short lived and so the pain quickly subsides.

�

Want to know why something happens Quiz The AnswerBank here.

�

by Lisa Cardy