All,

A preview of the poster presentation which I have prepared for ICT2017 has led to an exchange of correspondence between myself and Dr David Parker of the Oak Ridge National Laboratory – see attached below.

 I would be grateful if anyone who may be intending to visit my presentation in Pasadena, and who believes that they know the thermoelectric behaviour of dental amalgams, could please bring with them references to the findings of any scientific investigations carried out in order to measure it.

 Best regards,

 Keith P Walsh

  *****************************************************************************

Keith, thank you for sending this information - certainly something I would not have otherwise thought about.

One thing you might wish to consider in your investigations is that the Seebeck coefficient of most metals is no more than 10 x 10^-6 Volts/K, and that in the human mouth, where fillings are located, a typical temperature difference is likely no more than 1 K (1.8 F) or so.  This is different from Volta's case with hot water, which likely creates a 30 - 50 K temperature difference.

 A 10 ^-5 Volt potential in the human mouth would, if there were any physiological effects, conceivably be experienced directly in the mouth, more so than in a neurological capacity. I recall placing my fingers across the poles of a 1.5 V battery and one can feel a sensation - but that is several orders of magnitude more voltage than what these thermoelectric voltages are.  I would think it unlikely, though not inconceivable, that there would be physiological effects here.  Remember that most of the human body - skin, etc. - is insulating, not conducting, with much larger Seebeck coefficients, so that if Seebeck related effects were important in physiology we would see these already. But good luck with your researches, and have a safe trip to Pasadena.

 Sincerely,

 David Parker

 …………………………….

 Dear Dr Parker,

Thank you for your reply.

One of the principal themes of my poster presentation is that thermoelectric effects obtained from dissimilar metals in contact with each other are generally much greater than those obtained from single metals.

Volta produced palpitations in the frog's leg using a temperature difference of only 30 - 50K between the ends of a rod of a SINGLE metal. We should expect therefore that when Seebeck did a similar experiment using a coupling of two dissimilar metals, the required temperature difference should have been much less than this.

Indeed, both Volta and his contemporary Galvani had also done the same experiment with bi-metallic arcs, but had never cited the role of temperature difference for these at all.

It appears that Seebeck never succeeded in detecting any thermoelectric effect from single metals, but he did do so from a material which he knew to be inhomogeneous.

I know from experience that people tend to regard dental amalgam as a single material, but it is in fact more accurately described as an inhomogeneous mixture of dissimilar metals - much more inhomogeneous than, for example, any true alloy.

I think that in view of the fact that people regularly place foods in their mouths which differ significantly in temperature from that of body-temperature (ice-cream providing a potential temperature difference of up to 37K for example), then anyone with the ability to reason scientifically should now recognise that the thermoelectric performance of typical dental amalgams should at some time have been measured.

To illustrate this further I have attached a clipping from my poster. The lower diagram shows how a metallic inclusion in a material creates both a thermoelectric eddy current and an associated magnetic field whenever a temperature difference is applied across it. The magnetic field is detectable at the surface of the material, and this phenomenon is used for Non Destructive Testing purposes in metallurgy.

The upper diagram shows the microstructure of a typical dental amalgam, which takes the form of many inclusions of one conductive material all contained within a solid matrix of a different conductive material.

Can you think of an experiment which might demonstrate whether the magnetic field set up by this material as a result of the thermoelectric eddy currents induced by the application of a temperature difference across it can be detected at the surface? And, if so (and in view of the fact that amalgam fillings are placed in children's teeth), can you suggest why such an experiment should not already have been carried out?

The widespread introduction of amalgams for use in restorative dentistry was quickly followed by the rise to prominence of psychiatric "medicine" in our societies. I think that the question of whether any link of cause and effect between these two phenomena could have gone largely unrecognised for so long can only be answered by scientific (i.e. experimental) investigation.

Best regards,

Keith P Walsh