By the way, if anyone is curious about dental materials you might be interested in the statement issued a few years ago by the organisation "Health Canada", via the website of the Canadian Dental Association:

"It should be noted that Health Canada has taken the position that new amalgam fillings should not be placed in contact with existing metal devices in the mouth"

Well, as we know, dental amalgam is an inhomogeneous mixture of dissimilar metals in its own right. Not only that, but it has been common practice amongst dentists to screw metal alloy retaining pins into the root sockets of patients' teeth and encase the heads of the retaining screws in amalgam.

Our knowledge of thermoelectric effects tells us that, in addition to any thermoelectric activity which might arise from temperature gradients in the amalgam itself, such an arrangement might also be reasonably expected to provide further potential for the generation of thermoelectric emf and eddy currents along the contours of the interface between the amalgam and the retaining screw.

In view of these facts, I wrote to the Canadian Dental Association regarding the statement quoted above with the following query:

"Is this recommendation intended to apply to metal alloy retaining pins screwed into the root sockets of a patient's tooth?"

And I received the following reply from Dr Philip Neufeld of Health Canada:

"Dear Mr. Walsh:

Health Canada's position statement on amalgam recommended against placing amalgam fillings in patients who have existing metal devices because this results in having dissimilar metals in the mouth. Dissimilar metals set up galvanic currents which can cause two problems. First, they accelerate the corrosion of the amalgam. This leads to pitting, crevice formation, and marginal leaks, shortening the life of the filling. The corrosion also increases the rate of mercury vapour release.

Second, galvanic currents can cause a tingling sensation or a metallic taste in the mouth which are annoying to the patient. Sometimes the currents can cause inflammation or sores on the gums, tongue or the inside of the cheek in contact with the metals.

However, it is unlikely that a metal retaining pin implanted into the tooth or the jaw bone would cause galvanic currents. In order for galvanic currents to be created, the pin would have to be in contact with an electrolyte such as saliva or extracellular fluids, and such retaining pins are usually not exposed. Health Canada recognizes that although it is preferable to avoid dissimilar metals in the mouth, there may be situations where there is no practical alternative. Dental practitioners are therefore expected to take these factors into consideration in making decisions on treatment.

Yours sincerely,

Philip Neufeld, Ph.D."

- which left me with the distinct impression that he didn't know anything about the thermoelectric properties of metal dental restorations at all.

Keith P Walsh

TE Effects In Metal Dental Restorations

ITS Members may be interested to read what the website of the Canadian Dental association says regarding the placement of metal dental fillings in contact with other metal objects in the mouth:

"10. Is dental amalgam safe when it rests against another metal (e.g. braces) in the mouth?

It should be noted that Health Canada has taken the position that "new amalgam fillings should not be placed in contact with existing metal devices in the mouth, such as braces." Health Canada's concern is related to galvanic effect, which occurs when two different metals are in close proximity and create the potential for electric current to be generated.

Dentists are aware of the possibility of abutting metals creating a galvanic effect. It is also recognized that galvanic effect, through corrosion of metallic dental materials, may increase the release of mercury and other elements or compounds. Some recent evidence suggests that galvanic effect may also slightly increase the release of mercury vapour from amalgam.

For all these reasons, it is prudent for dentists, in suggesting a restorative material, to avoid creating a galvanic effect whenever patient care will not be compromised. It is also inadvisable to remove existing fillings unless the patient complains of symptoms which may be attributed to galvanic effect.

At the same time, the placement of orthodontic braces on patients with amalgam is often necessary and desirable, and has not been shown to be associated with ill effects. It may also be necessary, for the purpose of adequate restorative treatment, to place restorations in close proximity and to create the potential for galvanic effect.

CDA's Committee on Clinical and Scientific Affairs notes, however, that when amalgam has been in the mouth for a small a period of time, oxidation (corrosion), through a complex process, contributes to the reduction of electrical flow. Galvanic effect, apart from its potential to contribute to heavy metal body burden, has not been demonstrated to be harmful, and concerns about galvanic effect must be considered in the context of the patient's overall oral health care needs.

CDA has asked Health Canada for an annotated scientific bibliography supporting its unconditional recommendation on galvanic effect. If this information is received, it will be reviewed immediately and, if necessary, further advisories will be sent out to the profession and made available to patients."

This tends to confirm the view that the Canadian Dental Association doesn't know anything about the thermoelectric behavior of metal dental restoraions.

Keith P Walsh