Evaluation of the safety issue of mercury release from dental fillings

These tooth restorations, commonly known as “silver” fillings, contain 50% mercury by weight. However, it is apparent that the first summary highlight of the HHS Report is merely a reiteration of the American Dental Association’s (ADA) anecdotal position that the safety of mercury/silver fillings is based on popularity and long-term use (1). Even today, mercury/silver fillings remain the material of choice for most tooth restorations. The impression conveyed by the second highlight is that mercury fillings emit only minute amounts of mercury vapor. To the contrary; clear experimental evidence exists that the daily total mercury released (all forms) from a single mercury filling is approximately 15 g (2). The average absorbed dose of mercury vapor for human subjects with 8 such fillings is estimated to be 10 ig/ day, with a range that may exceed 100 jzg/day for some individuals (3, 4), and these estimations do not account for the additional exposure from micropartides or ionic mercury in the gastrointestinal tract. Mercury fillings have been shown to contribute approximately twothirds of the total human body burden of mercury (5). Moreover, experimental evidence in monkey demonstrates that the mercury absorbed from suchfillings can be readily visualized by whole-body image scan in a variety of body tissues (6). In contrast to the opinion stated in the HHS Report regarding minute amounts of mercury, the World Health Organization Expert Committee on Inorganic Mercury (3) concluded correctly that mercury fillings constitute thelargest single source of mercury exposure in the general population, greater than all other nonoccupational sources combined, including food, water, and air. The second highlight goes on to suggest that scant evidence exists that mercury fillings pose a health risk to most people. The real reason for this scant evidence (either for or against these fillings) is that the dental profession has historically failed to investigate this issue. Perhaps this is because dental materials experts have traditionally come from the ranks of materials engineering rather than from the biological sciences. Also, experts for the ADA have dismissed animal experimental studies as irrelevant to humans (7). On the other hand, medicine has been made aware only recently of this mercury tooth filling issue, and experimental evidence is now accumulating on several fronts (8). On the basis of present data, medical researchers (including ourselves) do not make any claims that amalgam mercury is the cause of a specific disease. But experimental pathophysiological evidence in sheep (9) and primate (10) models leads us to conclude that human health consequences might result from continuous exposure to mercury at levels released from mercury fillings. The possible role of dental mercury in Alzheimer’s pathogenesis also should not be overlooked (8). The third highlight recommends that a research program be directed at evaluating amalgam safety. This well-meaning statement was also the recommendation of the 1984 NIDR/ADA Workshop on the Biocompatibiity of Metals in Dentistry (11). Review of the literature reveals that dentistry has accomplished very little on this topic over the past decade. The next highlight states that the Public Health Service should educate dental personnel about risks and benefits of mercury fillings. Considering that mercury fillings have already been in use for 150 years, one would expect that a modem dental education would cover the risks and benefits of this commonly prescribed tooth implant material, as does a medical education with pharmaceutical prescriptions. The fifth highlight is vague, but the HHS Report recommends that mercury and silver alloy be classified and placed into the category of materials that are already considered safe, even though the U.S. Food and Drug Administration rules stipulate that where insufficient information exists about the safety of a product, it should be relegated to a category that requires experimental evidence of safety. Surely a product containing 50% mercury, a well-known toxin, should qualify only for the latter category. The sixth highlight states that there is insufficient evidence to assure the public that alternative dental filling materials are any safer than mercury fillings. If this is true, it is a telling commentary on the level of biological sophistication of a health care profession that each day implants dental materials and devices into millions of mouths. It is interesting that a January 1993 press release from the HHS (12) states that “there is no solid evidence of any harm for millions of Americans who have these fillings.”