It appears that many dentists are only able to discuss the electrical behavior of dental amalgams in terms of "galvanic activity" (after Luigi Galvani, who did some pioneering work in electrolysis).
However, it has been known for more than 150 years that when an electrical conductor moves in an electromagnetic field then an electrical potential is induced in the conductor, and that when a stationary conductor is subjected to a varying electromagnetic field then an electrical potential is again induced in the conductor; and it is not necessary in either case for there to be any electrolysis taking place in order for this to happen. (It was Michael Faraday who demonsrated the laws of electromagnetic induction in the 1830s.)
The materials used in restorative dentistry are not exempt from the laws of nature.
Does anyone know if it is possible to determine whether or not certain types of electromagnetic field are able to dissipate electrical energy through the nerves in people's heads as a result of faradaic activity in the amalgam fillings in their teeth?
Keith P Walsh
PS, for a definition of the word "faradaic" go to:
There are people who postulate that the type of metal amalgam which is formed by mixing liquid mercury with grains of a solid metal alloy at room temperature and allowing the mixture to harden is a suitable material for dentists to use for placing fillings in their patients' teeth.
I am certain that it is incumbent upon these people to have first taken all reasonable steps to demonstrate that such a material is not able to dissipate electrical energy through the nerves in people's heads as a result of its electromagnetic (or "faradaic") behavior.
Do you know if any of them ever have?
Keith P Walsh
PS, for a definition of the word "faradaic" go to:
I'm an electronic engineer so perhaps I can comment...
Which magnetic field you are worried about? I think the Earths magnetic field is about 4x10^-5T and other magnetic fields from power lines are typically lower than that. However fields of 20T - that's 500,000 times as strong don't appear to cause any ill effects on patients subjected to NMR scans. If the problem you describe exists thet would expect them to complain of pain in the teeth if they move while being scanned - I know they are told to stay still but some must sneeze or swallow occasionally!
What about pilots? They fly at hundreds of miles an hour through the earths magnetic field for perhaps 20-30 years of their life. I've not heard of any claims that this mechanism is making them ill or loose their teeth.
If you knew your subject better you would appreciate that the excitation of the nuclei of atoms in NMR procedures is not simply dependent upon field strength.
The field strength influences the frequency at which the targeted nuclei will resonate, but the frequency of the incident radiation must also match this "resonant" frequency in order to produce the required excitation.
The variation of resonant frequencies for varying field strengths is different for the nuclei of different elements. In fact, each element (more accurately, each isotope of each element) has its own characteristic profile of "resonant" frequencies (called Larmor frequencies after the British scientist Sir Joseph Larmor (1857-1942)).
A table of NMR frequencies at different field strengths for different elements can be found on the website of the Massachusetts Institute of Technology at:
You can see that the field strengths for this table have actually been chosen to match with convenient values of Larmor frequencies for hydrogen - H(1).
So, for argument's sake, if an NMR scan was set up with a field strength of 5.8717 Tesla and a frequency of incident radiation of 250 MHz, then you would expect the hydrogen nuclei in the region of the body under examination to "resonate" accordingly.
However, you would not expect the nuclei of the mercury, silver or tin atoms in your amalgam fillings to resonate significantly at all.
This is not because the field strength is not great enough.
It is because the Larmor frequencies of Ag(107), Ag(109), Sn(115), Sn(117), Sn(119), Hg(119) and Hg(201) at this field strength are
10.116, 11.630, 81.749, 89.063, 93.181, 44.568, and 16.499 MHz respectively, and not 250MHz.
The Larmor frequencies for these nuclei will always be different from that of hydrogen, whatever the strength of the field. And it is therefore possible to ensure that only hydrogen nuclei are excited in an MRI procedure simply by determining that the incident radiation matches the Larmor frequency for H(1) at the chosen field strength.
Do you think that it should be possible to determine whether or not the nuclei of the atoms in amalgam fillings are excited by the electromagnetic fields associated with visual display units, electrified railway lines, cellular telephones, etc., etc., etc.?
I think that your previous contribution stongly implied that in your opinion if it is demonstrated that a material does not resonate in an elctromagnetic field of a certain strength then it must be correct to presume that it will not resonate in any field of a lesser strength.
It isn't that simple. (Nature rarely is.)
If you followed my last message you will appreciate now that a material will resonate in an electromagnetic field of any field strength (no matter how small) if the frequency of the incident radiation matches the resonant frequency (or frequencies) for the material corresponding to that field strength.
Don't be too embarrassed. Your mistake is a common one.
And it explains why our understanding of the electromagnetic behavior of dental amalgams should be based on the results of scientifically conducted investigations rather than on the unsubstantiated guesswork of well-meaning but only partially informed "professionals" such as yourself.
You see, when it comes to the electromagnetic behavior of dental amalgams the dentists who frequent this newsgroup are just as ignorant as you are (if not more so). So when you announce yourself as an "electronic engineer" and start telling them things that they want to hear there is a danger that they will automatically assume that you know what you are talking about.
Let's stick to science.
Metal amalgam fillings are placed in children's teeth.
The electromagnetic properties of dental amalgams should therefore have been measured.
And the results should be available.
Would you not agree?
Keith P Walsh
PS, some of the basic principles of NMR technology are expained at:
- and further enquiries regarding the electrical properties of dental amalgams can be found at:
Nope. I've away been taking my kids on a steam train ride I got better things to do with my life than worry about my fillings. If you worry so much the stress will get you if the fillings don't.
Well actually I missunderstood your original post. I thought you were mainly interested in low frequency magnetic fields from things like power lines or monitors because you were talking about physical movement within a field. I was talking about movement within the intense "DC" magnetic field used in scanners not the RF excitation field. I understand and agree with your point about the frequency being tuned for hydrogen and not mercury.
The following is from the website of the Gore electronics company:
"If you can describe the permittivity, permeability and conductivity of a material, you can describe completely how electromagnetic energy behaves within that material. "
Permittivity is measured in farads per metre, permeability in henry per metre, and conductivity in siemens per metre.
Do you know of any reason why it should not be possible to measure these properties for a typical dental amalgam?
Keith P Walsh
PS, If you were ever to stand back and allow an ignorant dentist to place amalgam fillings in the teeth of those kids of yours then in my opinion that would make you just as ignorant as your own parents.
In recent years many millions of dollars have been spent on attempting to prove that the causes of so-called "psychiatric" conditions such as "schizophrenia", "paranoia", "sress" and "depression", etc., are "genetic".
So far without success.
I've noticed that there is something other than genes which silly parents pass on to their children who then grow up to be unhappy - a neglect for their teeth (usually coupled with the sheep-like acceptance of the notion that there is "nothing wrong" with amalgam fillings.)
Most of us have grown up in a society where having great clumps of mercury amalgam placed in our teeth is the norm.
What means do we have of determining that our anxieties, fears, listlessnesses and lack of confidence are not caused by the electrical behavior of these fillings?
Scientific investigation. That's what.
It is the natural function of the human neurological system to transmit signals in the form of tiny electrical currents.
However, it is not the natural function of the human neurological system to be permanently dissipating the electrical energy generated by metal amalgam fillings in teeth.
Amalgam fillings are placed in children's teeth.
The electrical and electromagnetic properties of amalgam s should therefore have been measured.
"This guy" has identified that the dental profession's confidence in amalgam fillings doesn't appear to be based on science at all.
It appears to be based on ignorance (and is perhaps dependent upon it.)
Do you know if anyone has ever carried out experimental investigations to measure the electromagnetic properties of a typical dental amalgam?
Keith P Walsh
PS, the properties of electrical conductivity, permittivity and permeability are measured in the SI units of siemens per metre, farads per metre and henry per metre respectively. Would you expect these properties to vary from point to point within a typical dental amalgam?
What is your position on taking the question of the electromagnetic properties of a typical dental amalgam to the physics department of the nearest college/university and asking them if they could answer those questions?
What is your position on the unwillingness of Keith P Walsh to take these questions to the physics department of the nearest college/university?
The only difficulty in assigning a measured value of resistivity to amalgam is that it is not a single material but a whole class of materials. Many different compositions are possible (similar to but the range of alloys possible that might be called solder). But the resistivity of any specific mixture is ordinarily measurable and all are metallic conductors.