Mark Richardson PhD.
This study made an estimate of the exposure of the Canadian population to mercury from amalgam, food, and the environment. The study did not include laboratory research or clinical investigations. It reviewed the international literature on the health effects of mercury and used sophisticated computer modelling techniques to calculate mercury exposure from amalgam. This calculated exposure was then used in standard risk assessment procedures to estimate a tolerable daily intake level (TDI) for mercury….
…Some studies have found evidence of slight sub-clinical impairment of cognitive functions, particularly short-term memory, in individuals exposed to fairly low mercury vapour levels. These effects are not easily detected, and the existing data do not allow the calculation of a no-effect threshold level.
One of the most important aspects of the study was that it calculated a Tolerable Daily Intake (TDI) for mercury and related that TDI to the estimated mercury exposure from amalgam. Such a calculation had not previously been attempted for mercury vapour…
The concept of a TDI is often used in setting guidelines to limit exposure to hazardous substances from industrial or environmental sources. A TDI for a substance is the level to which people could be exposed continuously over their lifetime without suffering any harmful effects.
…Because of uncertainties in the data, Dr. Richardson applied a safety factor of 100 to derive a proposed TDI for mercury vapour of about 1 µg/day for a 70 kg adult. His comparison of this TDI with the quantities of mercury absorbed daily by individuals with amalgam fillings indicated that four amalgam fillings should cause no observable adverse health effects in adults during a lifetime of exposure. However, Canadian adults with an average number of fillings (7) might exceed this limit….
Concerns over amalgam safety
The current concern has been prompted by a number of factors. Starting in 1987, the Federal Public Health Office of Germany issued a series of recommendations against the use of amalgam in certain situations primarily in pregnant women, children, and people with kidney disease.
Sweden has begun a plan to phase out the use of amalgam. As of July 1, 1995 Sweden has not allowed its use for patients under the age of twenty, and according to present plans amalgam will be banned entirely after 1997.
In December, 1990 the CBS television news show “60 Minutes” broadcast a program on dental amalgam which raised a great deal of public concern. One of the scientists interviewed on this program was Dr. Murray Vimy of the University of Calgary who had done a research experiment in which he had placed radioactively labelled amalgam fillings in the teeth of sheep. The results showed that the mercury quickly appeared in the body organs of the sheep, especially the kidneys. Dr. Vimy reported that the kidney function of the sheep had been impaired by as much as 60%.
In 1994, the BBC television series “Panorama” produced a program on amalgam entitled “Poison in Your Mouth” which added to the public’s perception that amalgam is hazardous. Numerous newspaper and magazine articles have also contributed to the debate.
In response to public concern and to numerous inquiries as to Canada’s position on the safety of amalgam, the Medical Devices Bureau of Health Canada began a study of the issue in 1992 with the aim of developing a statement on dental amalgam.
Regulatory status of amalgam in Canada
Dental amalgam and other dental filling materials are classed as medical devices under the Medical Devices Regulations of the Food and Drugs Act. The authority of the Act applies only to the sale of medical devices and not to their use by health care professionals.
In 1982, amendments to the regulations were passed requiring pre-market review by the Health Protection Branch of safety and efficacy data for all devices designed to be implanted in the body for more than 30 days. However, dental amalgam and most other dental materials currently in use were exempt from these requirements because they had been on the market prior to the enactment of the regulations. (A similar situation exists in the US, where regulations were established in 1976).
In January 1994 dental filling materials were explicitly excluded from the list of devices subject to pre-market review under the Medical Devices Regulations.
Even though dental materials are not subject to pre-market review, they are subject to the general safety provisions of the Food and Drugs Act and Medical Devices Regulations. The Branch has the authority to regulate the sale of such materials if there is a safety concern. To date, no regulatory measures have been invoked with regard to amalgam.