Dental Fillings

[curiosity]

Today whilst cutting the cheesecake out of it's foil! 3 of the adults present cringed and held their mouths. The kids asked why, and we said it was because of our fillings. They didn't get the same sensation despite having a filling. I know that fillings are different now,. But what is it that causes the reaction us adults had?

[Froggy_Queen]

Might be the mercury they used to put in the old amalgam.

[Belle Fast]

I think it is to do with different substances vibrating at different frequencies of sound, like when an opera singer hits a particular note and it can shatter a wine glass. It would be a different frequency for enamel and material fillings are made of. I think its the same as nails on a blackboard putting your teeth on edge - a high pitched noise giving you an uncomfortable sensation.

[MrXLA]

Its caused by the electric potential set-up when two differing metals are placed in contact. In this case the charge is disspitated through your metal/amalgam fillings close to are actually into the nerve chamber of your tooth.

By the way todays amalgam fillings still contain mercury.

[Octavius]

The filling is an ingenious Chinese invention, having been in use since as early as the 7th century. Chinese dentists used a mercury paste to fill decayed teeth, often to the ill health of their patients. Used as a suspension medium, the quicksilver paste held other metals, such as silver, tin and copper, in place until they were adhered to the tooth. The practice spread throughout the world, and by the 1830s came into common usage. Tin was also added to the common mixture, to combat the expansive properties of silver, which has been known to burst teeth under pressure.

So, until recent advances in dental composites in the 1980s, you were very likely to have received a amalgam filling. They are easily identified by their silvery black colour. Thus, dental science has allowed you to become a living battery!

The pain tinfoil creates feels like an electric shock in the sensitive root nerves of the filled tooth. This description is very accurate. It is an electric shock, of up to 2 volts.

Some dental amalgams contain up to five dissimilar metals. Galvanic action between the metals different electrical potentials creates an electric cell in the tooth, which can generate currents of up to 10 microamps, a huge spike over normal body nerve currents of 3 microamps. People with extensive fillings can actually measure a weak voltage in their mouth from this action. This is fine until an outside element is introduced.

When the tin foil is introduced, it acts as an anode to the filling's cathode. The natural electrolytes present in saliva create a 'salt bridge' and the magic happens. The contact essentially short circuits the cell. A weak current flows between the electrodes (tooth and tinfoil) and is detected by the sensitive nerve of the tooth as an unpleasant sensation. Zap Nnnggg!. To accompany the shock, a metallic taste can also be generated by tin ions released by the reaction.

[curiosity]

Fantastic Octavius! Thankyou.

[Belle Fast]

Hmm..... I am now puzzled, how would the charge transmit to all three adults?

[ann_h]

I don't think it's to do with fillings, I agree it's vibration and then habit/expectation.

The same as squeaky nails, or why I have to throw away the last bit of lolly before I touch the stick.

Still, I'm very pleased to find out why foil touching fillings does that shock thing, dh was talking about it recently.

[curiosity]

I know what you mean Ann, but it is a definate physical pain, and the metallic taste also.