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The Significance of Zeros

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Letter to the Editor, ADA News Bulletin (March 1998)

Dear Sir

It was disturbing to read Professor Roulet’s promotional blurb in the advertising for the March’98 conference in the October newsletter (pg 9). In it he claims the problems of amalgams on a small group of people and poor professional behaviour, and society’s lack of reflection on the meaningfulness of mercury exposure levels in the microgram range ( g =0.000001 gms). The clear inference is that the amount of mercury being discussed is so small that any concerns are misplaced. If indeed this was Professor Roulet’s inference, then the only poor professional behaviour in evidence is his ignorance of toxicology.

The number of zeros either before or after the decimal point has absolutely no meaning toxicologically. Quite simply, the more potent the chemical, the lower is the prescribed dose. Reference to a list of oral reference doses used by Health Canada reveals the lowest TDI (tolerable daily intake) to be that of dioxin which is shown as 10 picograms/kg body wt per day. One picogram is 1/1,000,000,000,000 of a gram, one million times less than a g. Does Professor Roulet decry the concern over dioxins because there are 12 zeros in a picogram? The ATSDR (Agency for Toxic Substances and Disease Registry) listings of toxic substances show mercury to be number 3 on their list of the 20 most toxic substances, behind lead and arsenic. The ATSDR’s allowable Minimal Risk Levels (MRL) for acute exposure are 0.02 g/m and for chronic exposure 0.014 g /m.

Pro-amalgam dentists manipulating zeroes to mislead is not new. Health Canada was recently forced to castigate the Canadian Dental Association for just such behaviour, disgraceful for a professional association! The simple fact is that in any situation where exposure from a source reaches or exceeds a reference dose, every risk assessment agency in the western world interprets that as a potential danger. With mercury from dental amalgams we are exactly at that point with some published research showing levels as high as 87.5 g/m .

If the Scientific Committee of the conference was really interested in an honest and open discussion on this issue it would have included Dr. Mark Richardson of Canada in their program, as did the British Dental Association (May 1996), the Swedish Council for Planning and Coordination of Research (November 1997), and as is being planned by the Norwegian Dental Association for their conference in Oslo (August 1998). Their failure to do so leaves the ADA exposed to the suggestion that it is more interested in the public relations approach of merely appearing to seek answers rather than really doing something substantial, such as inviting someone who actually knows something about the subject.

It is to be hoped that Professor Roulet’s expertise in his other areas of interest is significant enough to overcome a manifest difficulty in interpreting zeros otherwise the ADA will have wasted its money in bringing him to Australia.

Yours sincerely,

Roman Lohyn Melbourne


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