The following is my reply to the question as to why one might wish to measure the Seebeck coefficient of a typical dental amalgam, as posed by Professor Richard van Noort, dental Materials scientist at the University of Sheffield, UK.
****************START*******************************----- Original Message ----- From: "R Van Noort" To: "Keith P Walsh" Cc: Sent: Wednesday, May 28, 2003 4:07 PM Subject: Re: The Electrical Properties of Dental Amalgams
Dear Professor van Noort,
It has been demonstrated experimentally that dental amalgams generate electrical potentials with magnitudes of up to 350 millivolts (slightly more than one third of a volt). See:
In his "Master of Dental Surgery" thesis Peter Sheridan asserts that, "Electrical Reading of Restorations is particularly worthless", on the grounds that, "there is no consensus as to what these devices are actually measuring". See:
Metal amalgam dental fillings are placed in children's teeth.
I think that it is therefore more consistent with the established principles of scientific understanding, and incumbent upon the dental profession, that further investigations into the electrical behaviour of amalgams should be carried out until there IS consensus regarding what these measurements are telling us.
In my experience, the one aspect of the electrical behaviour of dental amalgam which dentists and dental material scientists feel most confident in being able to discuss is its electrochemical behaviour. Briefly, this is that the exposed surfaces of a newly placed amalgam tarnish as the result of a small degree of electrochemical corrosion. This action produces a thin layer of metal oxide (and/or chloride) which adheres to the surface and effectively prevents further electrochemical corrosion from taking place.
However, it appears that some if not all dentists and dental materials scientists are under the impression that this accounts for all of the electrical behaviour of the material.
Again I disagree.
For a start, metal oxides do not necessarily make good electrical insulators. So, whilst they may effectively seal the surfaces of amalgams from further corrosion, they would not necessarily prevent the passage of electrical currents arising as a result of electrical potentials generated by other electrical phenomena.
Moreover, it has been known for more than 160 years that metals, mixtures of metals, and dissimilar metals in contact with each other are able to dissipate electrical energy to their surroundings as a result of their thermoelectric behaviour, and that it is not necessary for there to be any electrolysis taking place in order for this to happen. See:
The inter-relation of thermoelectric and electromagnetic phenomena in inhomogeneous materials can be seen at:
In view of these facts I believe that a responsibility lies with those who advocate the use of metal amalgams in restorative dentistry to take all reasonable steps to demonstrate that these materials are not able to dissipate electrical energy through the nerves in people's heads as a result of their thermoelectric (not to mention electromagnetic) behaviour.
And according to the established principles of scientific understanding this would mean carrying out experimental studies to measure the thermoelectric properties of amalgams.
And the principal thermoelectric property of a material is its Seebeck coefficient (sometimes called "thermoelectric power", and measured in volts per kelvin).
If such investigations were to then demonstrate experimentally that the thermoelectric potentials generated by amalgam dental fillings are, for example, not large enough on their own to dissipate electrical energy through the nerves in people's heads then the assertion that this is the case would have some scientific basis.
Otherwise we are just guessing.
And amalgam fillings are placed in children's teeth.
It should be neither necessary nor possible for anyone to guess these things.
They should have been measured.
That is science.
I put it to you that the fact that you don't know what the thermoelectric properties of dental amalgams are is the principal reason why you appear to have concluded that they cannot be of any significance.
That isn't science.
It's just sheer blind arrogance.
You might more honestly consider that you are not allowed to know what the thermoelectric properties of dental amalgams are.
And you might also consider that if you yourself were to try to find out what these properties are, you too would be met with nothing but ridicule, sarcasm and derision.
I think that you would prefer to preserve your reputation as a dental materials "scientist", even if you do recognise that without the science then what you might actually be is an unwitting dental materials "apologist".
This reply has been posted to the usenet newsgroups sci.med.dentistry, sci.physics and sci.materials
Keith P Walsh
PS: Some scientifically coherent enquiries regarding the possible effects of the electrical behaviour of dental amalgams can be found at: