Does the mercury used in dental fillings pose a significant threat to human health

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MEDICINE

Does the mercury used in dental fillings pose a significant threat to human health?

Viewpoint: Yes, the mercury used in dental fillings is dangerous to human health and can cause a variety of adverse effects.

Viewpoint: No, the mercury used in dental fillings does not pose a significant threat to human health. To the contrary, mercury-based fillings are safe, affordable, and durable.

Although dentists have used dental amalgam to repair cavities in the teeth for more than 150 years, since the 1970s there have been claims that the mercury in dental fillings is responsible for a variety of health problems. Dental amalgam, the material used in so-called silver fillings, is a crystalline alloy composed of mercury (approximately 50%), silver, tin, and copper.

When made aware of the composition of dental amalgams, many people worry about the possibility that mercury might enter their body and have detrimental effects on their health. Chemists, however, note that when properly combined in the form of dental amalgam, the metals used to establish the proper hardness and durability of dental amalgams become tightly bound to each other in a form that is essentially safe, stable, and biologically inert. To make this point clear, Dr. Robert Baratz, president of the National Council against Health Fraud, explains that water is a chemical combination of hydrogen, a highly explosive gas, and oxygen, a gas that supports combustion. However, water does not explode or burst into flames.

A report on mercury fillings, titled "Poison in Your Mouth," that appeared on the television news magazine 60 Minutes on December 23, 1990, played a major role in disseminating the claims of Hal A. Huggins, America's best known "anti-amalgamist." Narrated by Morley Safer, the program included patients who claimed to have recovered from arthritis and multiple sclerosis after their fillings were removed. One woman said her symptoms of multiple sclerosis disappeared overnight. Critics of the program noted that because mercury levels actually increase when amalgam is first removed, such an instantaneous recovery from "mercury toxicity" is impossible. Moreover, periods of remission and deterioration are common in multiple sclerosis and arthritis. The program and the media attention it attracted caused many people to demand the removal of their mercury fillings.

Anti-amalgamists claim that chronic mercury intoxication is a multisymptomatic illness. That is, it allegedly causes a variety of symptoms, including anxiety, irritability, fatigue, outbursts of temper, stress intolerance, loss of self-confidence, indecision, timidity, excessive shyness, memory loss, headache, depression, insomnia, unsteady gait, numbness and pain in the extremities, muscular weakness, drowsiness, edema, increased salivation, hair loss, nausea, constipation, diarrhea, and metallic taste.

Huggins, a Colorado dentist, is probably the most influential leader of the attack on dental amalgams and conventional dentistry. Huggins graduated from the University of Nebraska School of Dentistry in 1962. Before he became involved in anti-amalgam issues, Huggins promoted the premise that many diseases are caused by an imbalance of body chemistry and that he could prevent or cure such conditions by prescribing specific diets. During the 1970s, Huggins adopted the theory that amalgam fillings were the cause of many modern diseases, such as multiple sclerosis, arthritis, depression, cardiovascular disease, digestive disorders, epilepsy, chronic fatigue, Hodgkin's disease, and Alzheimer's disease. Huggins promoted his views in his 1985 book It's All in Your Head: Diseases Caused by Mercury Amalgam Fillings, pamphlets, seminars, lectures, tapes, private consultations, and his Toxic Element Research Foundation. Huggins later claimed that dental fillings, root canals, and crown materials caused autoimmune diseases, amyotrophic lateral sclerosis, birth defects, leukemia, and breast cancer.

According to Huggins, removing and replacing mercury fillings would reverse many illnesses and restore health. By the 1990s Huggins's clinic was attracting hundreds of patients, who paid thousands of dollars to undergo the Huggins protocol, a complex treatment regimen that involved much more than simple removal of mercury fillings. For patients, the first step in the Huggins protocol was to become educated about dental toxicity by reading books written by Huggins. Treatment involved a team of dentists and therapists, including physicians, intravenous sedation personnel, acupressurists, nutritionists, and detoxification doctors. After performing a dental examination and taking "electrical readings" on fillings and crowns, the dentist would determine the specific order in which removals and restorations should be performed. Blood samples were obtained so that an individual diet could be prescribed, the immune system could be assessed, and a "compatibility" test could be performed to determine which dental materials should be used. A sample of hair was used to analyze minerals, such as lead, mercury, cadmium, sodium, potassium, and calcium. For patients who could not come to his clinic, Huggins offered a consultation service that evaluated patients who sent in samples of hair and filled out questionnaires.

The Colorado State Board of Dental Examiners revoked Huggins's dental license in 1996. During the revocation proceedings, administrative law Judge Nancy Connick found that Huggins had consistently diagnosed "mercury toxicity" in all patients, even those without amalgam fillings, and had extracted all teeth that had had root canal therapy. The judge concluded that Huggins's treatments were "a sham, illusory and without scientific basis." Nevertheless, Huggins continued to write, publish, lecture, engage in consultations, and gain media attention for his attack on dental amalgam. Groups that support Huggins's conclusions include the American Academy of Biological Dentistry. In 1999, Huggins and Javier Morales, a Mexican dentist who followed the Huggins protocol, established the Center for Progressive Medicine in Puerto Vallarta, Mexico. By 2002, Huggins had published more than 50 articles and books on nutrition, child development, mercury toxicity, root canal, and cavities. His books and tapes include Amino Acids, Dentistry and the Immune System, Mercury Issue Update, Further Studies on the Amalgam Issue, Why Raise Ugly Kids?, Mercury & Other Toxic Metals in Humans, and Uninformed Consent.

Major national and international medical and dental organizations have investigated the safety and stability of dental amalgam and have concluded that the mercury in fillings does not pose a health hazard. A report issued by the U.S. Food and Drug Administration (FDA) in March 2002 concluded that "no valid scientific evidence has ever shown that amalgams cause harm to patients with dental restorations, except in the rare case of allergy." The U.S. Public Health Service concluded that there was no significant evidence that "avoiding amalgams or having existing amalgams replaced will have a beneficial effect on health." These conclusions have been supported by the American Dental Association (ADA), World Health Organization, European Commission, Swedish National Board of Health and Welfare, New Zealand Ministry of Health, and Health Canada.

Despite the evidence presented by the ADA, reputable medical groups, and public health organizations, anti-amalgamists have attempted to prohibit the use of dental amalgam. At the national level, legislators who have tried to ban dental amalgams include U.S. Representatives Diane Watson (D-Calif.) and Dan Burton (R-Ind.). Watson's bill, the Mercury in Dental Filling Disclosure and Prohibition Act, would amend the Federal Food, Drug, and Cosmetic Act to "prohibit the introduction of dental amalgam into interstate commerce" and would become effective January 1, 2007. A similar bill sent to the California legislature was defeated in committee, but in 1992 Watson succeeded in getting the California legislature to pass a law that requires the state dental board to issue a document listing the risks and efficacies of dental materials. The document issued by the dental board stated that "small amounts of free mercury may be released from amalgam filings over time" but that the amounts are "far below the established safe levels."

Watson's Mercury Prohibition Act would ban the use of amalgam in children younger than 18 years and in pregnant and lactating women and would require a warning that dental amalgam "contains mercury, which is an acute neurotoxin, and therefore poses health risks." Major scientific, medical, and dental associations oppose the bill and note that Watson's propositions are unfounded and that she apparently does not understand the fact that different forms of mercury have different properties and levels of toxicity.

Perhaps in the not too distant future the controversy over mercury in dental amalgam fillings will become moot because advances in science will fundamentally change the kinds of materials used to restore teeth and the way in which dentists prevent and treat cavities and gum disease. Dental problems eventually may be treated at the molecular level rather than with mechanical and surgical procedures.

—LOIS N. MAGNER

Viewpoint: Yes, the mercury used in dental fillings is dangerous to human health and can cause a variety of adverse effects.

In today's world, many people are concerned about the environment. This is not surprising when one considers the numerous industrial poisons that have become prevalent in the natural world. Worrying about toxins that might be in the air, our food, and the water we drink has become commonplace. News programs and public announcements seem to warn us daily about new health dangers. Many of us have heard about the things we need to avoid to protect our health. However, despite the new health consciousness that has permeated our culture, some of us might be shocked to realize that we already have one of the world's most dangerous poisons in our mouths: mercury.

Mercury, also known as quicksilver, is extremely toxic. In their book Deadly Doses: A Writer's Guide to Poisons, Serita Deborah Stevens and Anne Klarner indicate that a person weighing 150 pounds (68 kg) could experience a lethal dose by ingesting less than a teaspoon of the material. Although mercury can be ingested and absorbed through the skin, most poisonings come from the inhalation of mercury vapor that escapes from amalgam fillings when a person chews. In an article on mercury toxicity, Keith Sehnert, Gary Jacobson, and Kip Sullivan, a physician, dentist, and attorney, respectively, stated that the vapor can enter the bloodstream and be delivered to all parts of the body, including the brain. They emphasized that people with amalgam fillings have higher levels of mercury in their urine, blood, and brain than do people without amalgam fillings. In a study from the University of Calgary, M. J. Vimy, Y. Takahashi, and F. L. Lorscheider, faculty in the department of medicine, found that pregnant sheep with new amalgam fillings had elevated levels of mercury in their fetuses within two weeks of the placement of the fillings. The investigators concluded that mercury travels to the gastrointestinal tract, kidney, liver, and brain.

Mercury vapor is produced when the chemical boils at 40°F (4°C). That is why, for example, the chemical is so useful in thermometers. According to Stevens and Klarner, with high concentrations of vapor, the victim usually dies of ventricular fibrillation (abnormal heart rhythm) or pulmonary edema (excessive fluid in the lungs). Mercury builds up in the body, so smaller doses could eventually accumulate into dangerous levels. These lower-level poisonings can lead to numerous neurological diseases, including muscle tremors, hallucinations, migraines, and even psychosis.

The ways in which people suffer from having amalgam fillings vary. Some people may feel acute symptoms; others may appear to be completely unaffected. Nonetheless, anyone with amalgam fillings has at least some mercury built up in the body. Vasken Aposhian, professor of cellular and molecular biology at the University of Arizona, was quoted in an article by Francesca Lyman for MSNBC as saying that the number of amalgam fillings one has is highly important in terms of how much mercury the body absorbs. Of course, exposure to mercury can come from different sources; however, a large number of researchers agree that the greatest exposure comes from amalgam dental fillings. At a congressional hearing, Aposhian emphasized the seriousness of this exposure and stated that pregnant women should be especially careful, because mercury can cross the placenta and harm the developing nervous system of the fetus.

The United Kingdom Department of Health has issued warnings that pregnant women should avoid amalgam fillings, and the New Zealand Ministry of Health is reviewing its policy on the use of mercury amalgam for tooth fillings. In a letter to the editor of the New Zealand Medical Journal, Dr. Michael Godfrey, a leading environmental physician, brings attention to the fact that several major amalgam manufacturers issue material safety data sheets and directions for use that warn dentists of the many dangers associated with amalgam use. Warnings against using amalgams next to fillings containing other metals, in patients with kidney disease, and in pregnant women and children younger than six years are only some of the restrictions mentioned. The manufacturers warn that even in low concentrations, amalgam fillings can induce psychiatric symptoms, such as depression and mental deterioration. Given the seriousness of these warnings, it is not surprising to learn that many of Godfrey's patients who have chronic fatigue have an average of 15 amalgam fillings and display many of the symptoms the manufacturers warn against.

Considering the health risks mercury poses to human physiology, it is difficult to understand why anyone would want to put even the tiniest amount in his or her mouth. Yet amalgam dental fillings have been used for quite some time. An April 2001 news release presented by Bio-Probe Inc. discussed how the ADA at first denied that leaks of mercury vapor could occur from what are commonly called "silver" fillings. However, the ADA later modified its stand when numerous studies pointed to the contrary. The vapor leaks from these fillings, which typically consist of 48%-55% mercury, are now being linked to several health problems. In fact, some dentists refuse to fill their patients' teeth with mercury amalgam, choosing to use a safer composite material instead.

The Bio-Probe news release also presented findings based on data from the National Health and Nutrition Examination Survey (NHANES III). This study, according to the mission statement of the National Center for Health Sciences, is critical because the results can ultimately influence public health policy in the United States. With the help of a company in California that specializes in statistical analysis, links between dental fillings and adverse health conditions were sought. The study showed that 95% of those surveyed who were classified with disorders of the central nervous system, such as epilepsy and multiple sclerosis, had dental fillings. It also was found that although 18% of Americans are filling free, 33% of the survivors of circulatory disorders, such as heart and arterial disease, are filling free. Ernie Mezei, an activist with Citizens for Mercury Relief, who is also a chemist and electrical engineer, stated, "clearly the survivors of heart disease have a much higher rate of being dental filling free, and we know heart disease is the number one killer in the United States." In a study led by Jukka T. Salonen, M.D., at the University of Kuopio in Finland, researchers found that mercury exposure and heart disease were clearly linked. The researchers also reported that a clear correlation exits between amalgam fillings and the risk of heart attack. Although the circulatory and central nervous systems are known to be the major areas damaged by mercury exposure, the risks to human health do not stop there.

The ADA is well aware of the dangers attributable to the improper handling of dental amalgam. The spokeswoman for the International Academy of Oral Medicine & Toxicology, Pam Floener, was quoted in the Bio-Probe News as follows: "The metallic mercury used by dentists to manufacture dental amalgam is shipped as a hazardous material to the dental office. When amalgams are removed, for whatever reason, they are treated as hazardous waste and are required to be disposed of in accordance with OSHA regulations. It is inconceivable that the mouth could be considered a safe storage container for toxic material." Even with this knowledge, the dental profession itself has not been without its tragedies. In Deadly Doses, Stevens, a registered nurse, and Klarner present a case history involving a middle-aged dental assistant who died of mercury intoxication attributed to her regular handling of amalgams with 40% mercury compounds. In her article for MSNBC on the safety of dental fillings, Francesca Lyman pointed to a study from scientists at the Battelle Centers for Public Health Research and Evaluation in Seattle that linked exposure to mercury vapor from dental amalgam fillings to central nervous system toxicity among dental personnel.

Continuing studies have begun to uncover even more health problems related to mercury exposure. Some connections are being drawn between mercury exposure and Alzheimer's disease. The Web site <http://www.holisticmed.com> highlights a significant study led by the renowned researcher, Dr. Boyd Haley. In the study, rats were exposed to mercury vapor in a way that accounted for the size difference between humans and rats. The tissue damage that developed in the rats was described as being "indistinguishable" from Alzheimer's disease. Haley was quoted as saying, "I'm getting the rest of my fillings taken out right now, and I've asked my wife to have hers replaced, too." This is especially troubling because not everyone agrees on the level of risk, which complicates the issue even further. Although not everyone agrees that it is necessary to have a patient's amalgam fillings removed, interesting studies have been conducted on the subject. One such study involving 118 subjects was conducted by H. Lichtenberg, a dentist in Denmark, and the results were published in the Journal of Ortho-molecular Medicine. After the amalgam fillings were removed, 79% of the symptoms experienced by the subjects were reduced or eliminated. The results also indicated that patients with mild reactions to metals were more likely to have fewer or no symptoms than were patients with strong reactions to metals.

Despite the mounting epidemiological data, many organizations such as the ADA continue to ignore the risks posed by the use of mercury amalgam dental fillings. Furthermore, dentists have not been prevented from placing approximately 80 million of these fillings in American mouths each year. This practice seems almost ludicrous when one considers that mercury poisoning commonly causes gingivitis, damage to the gum line, and loosening of the teeth. An interesting analogy posed by Sehnert and his coauthors helps to illustrate the gravity of the situation. They point out that in general an amalgam filling weighs 1 gram, which is half mercury, and that if half a gram of mercury were to find its way into a 10-acre lake, a fish advisory for the lake would be warranted. Therefore it is no surprise that many people are calling for a ban on the use of mercury amalgam. Sweden has already banned it. Health authorities in Austria, Canada, Denmark, and Germany are trying to restrict the use of amalgam. Legislation requiring informed consent has been passed in California, and Representative Watson has proposed legislation to ban mercury amalgam altogether. Opponents to the legislation might argue that there are not many other options, and sadly, they would be correct. The materials available for dental fillings are composites, which come in a variety of brands, and mercury amalgam. To complicate matters, some dentists believe that composite material is not as durable as mercury amalgam, especially when used to fill molars. This often leaves patients and dentists with difficult and limited choices. Research is needed to develop a wider range of safe and durable products that can be used to fill teeth. In the meantime, this does not mean that we should quiet the controversy or turn a blind eye to the problem.

In an editorial in the Bio-Probe News, Sam Ziff states that many Americans are simply unaware of the multiple health risks associated with amalgam fillings. In Ziff's opinion, not enough is being done, and it must be made very clear to the public that amalgam fillings not only leak mercury vapor but also do so continually. This vapor is then directly inhaled into the lungs, where 80%-100% of the toxin is absorbed. As of yet, there are no scientific data for determining the least amount of mercury that will not cause cellular damage. It is known, however, that the longer a person is exposed to mercury vapor, the higher the dose will be. Therefore the problem must be dealt with immediately, not some time in the future. After all, the controversy over amalgam dental fillings is not new; it has been around for more than 150 years. However, the fact that dentists have been filling patients' teeth with amalgam for so long has been one of the arguments the ADA has embraced to justify its use. As each year passes, more Americans will have pieces of deadly toxin placed in their mouths. "We've always done it this way" no longer seems an appropriate justification. Perhaps Lord Baldwin, joint chairman of the British Parliamentary Group for Alternative and Complementary Medicine, said it best: "To point to the fact that amalgam fillings have been used for a hundred years is not a proof of safety anymore than it is a proof of safety to claim that tobacco smoking must be safe because people have been smoking for a long time."

—LEE ANN PARADISE

Viewpoint: No, the mercury used in dental fillings does not pose a significant threat to human health. To the contrary, mercury-based fillings are safe, affordable, and durable.

Dental amalgam, the material used in silver fillings, is approximately one-half (43%-54%) mercury. The other half is composed of an alloy containing silver, tin, and copper. Each of these elements by itself can be poisonous if taken into the body in sufficient amounts. Mercury, in particular, is known for its toxicity—the ability to cause injury to the body by chemical means. On the surface, it seems quite plausible that the mercury in fillings might slowly poison the body and cause a host of health problems. Plausible, but wrong. This argument is disproved by a basic fact of chemistry: The mercury in dental amalgam chemically binds to the other elements; the result is a substance that is hard, stable, and safe.

Dental amalgam has been used for more than 150 years. During that time, particularly over the last decade, its safety and effectiveness have been studied extensively. In March 2002, the FDA issued a consumer update on the findings of these studies. The FDA concluded that "no valid scientific evidence has ever shown that amalgams cause harm to patients with dental restorations, except in the rare case of allergy." Other major national and international organizations reached similar conclusions after reviewing the research. They include the ADA, U.S. Public Health Service, World Health Organization, European Commission, Swedish National Board of Health and Welfare, New Zealand Ministry of Health, and Health Canada.

Birth of a Health Scare

If amalgam fillings are safe, why are people so worried about them? In the United States, much of the public concern can be traced to Hal Huggins. In the 1970s, Huggins began promoting a theory that amalgam fillings were at the root of a wide range of modern ills, including multiple sclerosis, depression, heart and blood vessel problems, arthritis, some cancers, chronic fatigue, digestive disorders, and Alzheimer's disease. Huggins went on to publish books and pamphlets and make videotapes and media appearances in which he advocated having amalgam fillings removed and replaced. By the early 1990s, Huggins's center was treating more than 30 patients per month, many of them desperately ill. The patients were charged up to $8,500 each for two weeks of intensive therapy. Huggins's dental license was revoked in 1996, but he continues to publicize his controversial views.

Meanwhile, other voices have joined the anti-amalgam chorus. Much of the outcry has been fueled by the media, including the report that aired on 60 Minutes in 1990. Among the more outlandish claims made in that program was the story of a young woman with multiple sclerosis who said that on the very day her fillings were removed, she was able to throw away her cane and go dancing. Considering that the act of removing amalgam fillings actually temporarily increases mercury levels in the body, this sounds more like the power of positive thinking than a medical miracle. Yet just months later, nearly half of 1,000 Americans surveyed by the ADA said they believed dental amalgam could cause health problems. The level of public fear and misinformation is still high. In fact, the situation is so bad that the American Council on Science and Health, a nonprofit consumer education organization, has branded it one of the "greatest unfounded health scares of recent times."

A Question of Quantity

The unfortunate truth is that most consumers and even many dentists have heard only one side of the story. They are not aware of the large body of research backing up the safety and benefits of dental amalgam. One key question is how much mercury exposure is too much. It is true that some mercury vapor may be released from amalgam fillings by chewing or tooth grinding. However, the exposure lasts only a few seconds, and the amount taken into the body seems to be extremely small. It is worth noting that mercury is already everywhere in our environment, including our water, air, and food, especially fish. Although high levels of mercury are toxic, the lower levels that most people encounter every day, whether or not they have amalgam fillings, do not seem to pose a health risk. It is a classic example of the scientific principle that "only the dose makes a poison." This is the same principle that explains why drugs and even vitamin supplements can be helpful in small doses but harmful in excess.

One difficulty lies in measuring precisely how much mercury is released by and absorbed from amalgam fillings. The process can be affected by everything from how many teeth a person has to how he brushes them, and from how someone eats to whether she breathes through her mouth. Currently, the amount of mercury in the body is measured through analysis of breath, blood, and urine, but these methods need improvement. It still is difficult to discern whether mercury found in the body comes from fillings or other sources. Nevertheless, the best evidence indicates that the amount of mercury released by fillings is inconsequential.

Some of the most compelling data come from studies of dentists. Because dentists breathe in mercury vapors every time they insert or remove an amalgam filling, it stands to reason that their risk should be considerably greater than that of the average person. Studies have shown that dentists do tend to have higher levels of mercury in the urine than does the general population. Yet dentists still have no greater risk of illness or death. In other words, even dentists' above-average mercury levels do not seem to be high enough to cause harm.

A number of studies have compared the health of people with amalgam fillings and the health of those without amalgam fillings. These studies failed to support the claims of any related health problems other than rare allergic reactions. Even when researchers compared people who believed they had filling-related health problems with those who had no such complaints, they found the level of mercury was similarly low in both groups. This finding is revealing, because a true toxic response should show up on a dose-response curve—a graph of the relation between the toxin and the symptoms. The more severe the symptoms, the higher the exposure to the toxin should be. Yet researchers found no link between the severity of symptoms blamed on amalgam and the number of fillings people had or the level of mercury in their blood or urine.

Drilling Out the Filling

There are still plenty of people who truly believe they have problems caused by dental amalgam or who swear by the benefits of having old fillings replaced. A new term—amalgam illness—has even been coined for the catchall set of vague symptoms that have been attributed amalgam fillings. For some of these people, the problem may lie more in the mind than in the head. Several studies have shown that people who claim to have amalgam illness are more likely than others to have signs of various psychological disorders. For other people, the physical symptoms may be rooted in a very real medical condition, such as multiple sclerosis or Alzheimer's disease. Sadly, it is not uncommon to hear of seriously ill people having their fillings replaced in a vain attempt to find a cure for an incurable ailment. At the very least, these people are risking disappointment. A bigger danger is that some may give up standard medical care in the false belief that all they need to do is get their teeth fixed.

After having their amalgam fillings removed and replaced with another material, some people say they feel better, at least for a time. However, this is likely the result of the placebo effect—a well-known effect in medicine in which improvement after a treatment is caused by the person's positive expectations, not by the treatment itself.

There is no scientific evidence that removing perfectly good fillings has any beneficial effect. To the contrary, having fillings removed is expensive and often painful. In addition, it damages healthy tooth structure, which must be drilled out to accommodate the new filling. Ironically, replacing a filling also may expose people to more mercury than if the tooth had been left alone, because drilling into the filling releases mercury into the air. Of course, old fillings may eventually have to be replaced anyway, when they start to wear away, chip, or crack. Most dentists stop short of encouraging patients to replace sound fillings.

As long as there are people willing to pay to have fillings removed unnecessarily, there will be dentists willing to do it. A few have resorted to rather dubious tests to justify the procedure. For example, some use a symptom questionnaire that asks about a wide range of medical problems and a long list of symptoms, such as tiredness, boredom, and restlessness. The list is so inclusive that almost everyone would have some of the signs. Other dentists use an industrial mercury detector, which seems reassuringly objective. However, the amount of mercury released varies throughout the day, depending on what a person is doing. The test typically is done by having the person chew gum vigorously for several minutes, then checking the breath for mercury. This reading is used to estimate the total daily dose. Because chewing briefly releases mercury, the estimate is likely to be much too high. Even blood testing is of limited value, because blood concentrations are so low—typically less than 5 parts per billion—that they are difficult to detect and too small to identify the source of the mercury.

Hard Numbers versus Soft Science

Then there is urine testing. It may sound frightening to detect mercury in a person's urine. Remember, however, that mercury is all around us. As a result, most people, with or without fillings, have up to 5 micrograms or so of mercury per liter of urine. Practicing dentists typically have urine mercury levels of approximately 10 micrograms per liter or less. To put these numbers in perspective, the legal limit on mercury exposure for industrial workers is 50 micrograms per cubic meter of air, eight hours per workday, 50 weeks per year. Exposure to this extent produces urine mercury levels of approximately 135 micrograms per liter—more than 13 times the usual level found in dentists. Yet even this amount of mercury exposure is considered safe.

The fact is, amalgam fillings are needed in dentistry. They are safe, relatively inexpensive, and long-lasting. Although there has been a push in recent years to find new and better alternatives, amalgam still can hold its own against other filling materials. No other material is as versatile or easy to put in place. And unlike some materials, amalgam can be used to fill large cavities on stress-bearing areas of the teeth. There are some disadvantages, of course. Perhaps the biggest is appearance. Because many people do not want a silver filling to show, composite resins—tooth-colored, plastic filling materials made of glass and resin—often are used on front teeth or wherever a natural look is important. As far as health goes, however, the main risk of amalgam seems to be an allergic reaction. Yet such reactions appear to be quite rare. Fewer than 100 cases have been reported.

Despite the solid track record of amalgam, some people would still like to see it banned. The latest tactic is to attack amalgam through lawsuits and laws. The bill introduced by Representatives Watson and Burton in April 2002 if passed would ban the use of dental amalgam in the United States by 2007. A statement by Watson outlining her reasons for the bill shows the kind of muddled science that has given amalgam a bad reputation. Watson said that "mercury is an acute neurotoxin." In truth, although mercury can be toxic in some forms, the mercury in amalgam is chemically bound, making it stable and therefore safe. Watson goes on to say that the mercury in fillings constantly emits "poisonous vapors." The truth is that the minuscule amount of mercury that the body might absorb from fillings is far below the level known to cause health problems.

It is impossible to prove anything 100% safe. Yet dental amalgam is the most thoroughly tested material in use for dental fillings, and its safety remains unchallenged by mainstream scientific groups. The risk posed by the mercury in fillings seems to be minimal to none. On the other hand, the danger of losing a valuable option because of nothing more than unfounded fears and emotional arguments is quite real.

—LINDA WASMER ANDREWS

KEY TERMS

AMALGAM:

The material used in silver dental fillings. It is composed of approximately equal parts mercury and an alloy containing silver, tin, and copper. It is solid or liquid at room temperature according to the proportion of mercury present.

AMALGAM ILLNESS:

The set of symptoms sometimes attributed to dental amalgam.

COMPOSITE RESINS:

Tooth-colored, plastic materials made of glass and resin and used in some dental fillings.

DOSE-RESPONSE CURVE:

A graph of the relation between a toxin and its symptoms.

PLACEBO EFFECT:

An effect in medicine in which improvement after treatment is caused by the patient's positive expectations not by the treatment itself.

TOXICITY:

The ability to cause injury to the body by chemical means.

MERCURY AND THE MAD HATTER

It was no "tea party" for the makers of the very popular felt top hats in Victorian England, whose occupational disease gave rise to the popular expression of the day, "mad as a hatter," the inspiration for Lewis Carroll's famous character in Alice in Wonderland. The demented host of "A Mad Tea-Party" exhibited symptoms all too commonly found among hat makers in the nineteenth century, symptoms of mercury poisoning.

Hat makers worked in poorly ventilated rooms. They dipped the furs used for the felt hats in hot mercuric nitrate solution as they shaped the felt to make the hats. The workers readily absorbed mercury through their skin in the process. Their shaking and slurred speech were so common that the symptoms were described as the hatter's disease. In the United States, Danbury, Connecticut, was a center for the hat industry. There the symptoms of mercury poisoning were so common they were called the "Dan-bury shakes." Mercury is no longer used in the hat business.

Mercury poisoning was not unknown at the time of Alice's famous tea party. Pliny, the Roman philosopher and author of Natural History, in approximately a.d. 50 described the poisonous nature of mercury. In his work Pliny described a method for cleaning mercury by squeezing it through leather. He also noted that laborers in mercury mines were dying at work.

Although it is speculation, there are indications Isaac Newton was a victim of mercury poisoning. For a time Newton turned from his interest in physics to alchemy. Around 1690 he wrote in his notebook about heating mercury. For approximately three years Newton was reclusive, suffering from the typical mental and physical symptoms of mercury poisoning.

As ancient as the knowledge is, mercury continues to take victims. In 1997 a Dartmouth College chemistry professor died of acute exposure to probably the most toxic compound of mercury, dimethylmercury, when less then half a milliliter was spilled and went through the disposable latex gloves the scientist wore for protection. By the time the symptoms were diagnosed, the poisoning had progressed too far to save the victim.

—M. C. Nagel

Science in Dispute