Symposium

Dental Silver Amalgam Fillings Are Dentists Poisoning Their Patients

In the 1970s  A Colorado Dentist Hal Huggins started claiming that mercury in amalgam dental fillings caused a wide variety of diseases. In 1985 he published a book detailing his beliefs about “mercury toxicity.”1 Since that time the antiamalgam movement has grown substantially. Popular-health writers have also warned of the potential “dangers” of amalgam fillings.2-3 

Abstract: Dental amalgam fillings have a long history of use. In recent years a group of dentists, physicians, and “holistic” health-care advocates have questioned the safety of amalgam because of potential toxicity from the mercury in these dental restorations. Because of the relative low cost, ease of placement, strength, and longevity of amalgam fillings, the discontinued use of this material could lead to a large increase in dental costs with the result that more Americans would find it difficult to afford dental care. The public and professionals have been influenced by case reports in the medical and dental literature, research published in the refereed literature, and media stories that have implied that dental amalgam may be a causal factor for a host of diseases and conditions. This paper examines and analyzes the data both supporting and condemning the continued use of amalgam fillings. The author concludes that the evidence supporting the safety of amalgam fillings is compelling.

In December of 1990 CBS television’s popular program 60 Minutes presented a segment, “ls There Poison In Your Mouth?” which suggested that the mercury in these silver-colored dental fillings could cause diseases such as multiple sclerosis and arthritis that could be remedied by removing the fillings. 4 Thousands of viewers besieged their dentists with requests to have their amalgams replaced, and two New Mexico state legislators introduced a bill to ban amalgam fillings. 5 

A 1991 consumer survey, conducted by the American Dental Association (ADA) following the 60 Minutes story, reported that 48% of dental patients believed that they should be concerned that they might develop “health problems from silver fillings in their teeth.”6 

The furor that the 60 Minutes segment produced led the Public Health Service (PHS) to undertake a costly and intensive study of amalgam fillings. The PHS report found “scant evidence that the health of the vast majority of people with amalgam is compromised, nor that removing amalgam fillings has a beneficial effect on health.”? 

Amalgam Fillings and Public Health

Tin-mercury dental fillings were used in China over 1300 years ago.8 Today, dental silver-amalgam fillings (amalgams) are made of an alloy of silver, copper, tin, zinc, and elemental mercury (quicksilver). Silver-mercury restorations were first introduced to the Western world in France in the 1830s. In 1896, Dr. G. V. Black, the father of American dentistry, published a detailed scientific report advocating the use of amalgam,9 but it still took many years for Black’s conclusions to be universally accepted by the dental profession. 

In 1926, questions concerning the safety of amalgam fillings were raised in Germanv.l? In 1930, a report that validated the safety and continued use of amalgam was published by a committee specifically established to investigate these allegations. 11 

In a recent survey, 76.3% of American dentists preferred amalgam for the restoration of cavities between the teeth and 73% reported that amalgam was their first choice for restoring children’s primary molars (baby teeth).12 Because of amalgam’s relatively low cost; ease of placement; strength; longevity; and resistance to the corrosive effects of food, drink, and saliva, amalgam has long been the favorite restorative material of dentists worldwide. The widespread use of amalgam has been a public health boon, saving millions and millions of teeth from extraction. 

Research clearly shows that amalgam fillings can provide satisfactory performance for more than 12 years. 13 This is true even for large fillings that replace a significant amount of tooth structure.14 Yet, in spite of these data, there has been a steady decline in the use of amalgam.12 In a recent survey, 8. 7% of dentists wanted to ban amalgam use, while another 14.3% were undecided about its safety. 15 

Lack of confidence about the safety of amalgam fillings as well as the advent of aesthetic tooth-colored filling materials have caused a decrease in the use of amalgam. Since the aesthetic fillings are more expensive and less durable than amalgam, their increased use will inevitably lead to higher costs for dental care. 

Mercury and Its Compounds 

Every year between 2700 and 6000 tons of mercury are released from the oceans and the earth’s crust into the atmosphere. 16 Another 2000 to 3000 tons are released from human activities such as burning household and industrial waste and, especially, from fossil fuels such as coal. 16 Hippocrates was aware of mercury’s toxicity, 17 yet mercury still has a long history of use in medicaments (e.g., Mercurochrome, an antiseptic), and it is currently used in electrical applications, chlorine production, and dental restorations. The classic example of mercury poisoning occurred in the 19th century to felt-hat makers because mercuric-nitrate solutions were used to soften the felt. Many workers absorbed high amounts of mercury through their skin and lungs and developed tremors, incoherent speech, difficulty in walking, and weakened mental functioning. The problem was immortalized by the Mad Hatter in Alice in Wonderland. 18 Even today, mercury can be a hazard for workers in thermometer factories and in plants that use mercury to make chlorine and caustic soda. 18 

The most toxic mercury compounds are methylmercury and ethylmercury; mercury vapor is less toxic and inorganic mercuric salts and organic forms of mercury such as phenyl mercury salts are the least toxic. 19 In the oceans, certain bacteria transform elemental mercury into the highly toxic methyl mercury, which moves up the food chain and can concentrate in fish and potentially poison humans. Fish that were contaminated in this fashion were responsible for death and chronic disturbances in Minamata, Japan. Developmental defects were also caused and are now known as Minamata Disease. 20 The minimum dose needed to develop symptoms was 5 mg per day of methyl mercury.21 

The half-life of methyl mercury is about 70 days in adults and slightly longer in the fetus. 22 Approximately 15% of the body burden is in the brain.22 

In 1983 it was reported that oral streptococci could transform elemental mercury into methyl mercury, in vitro.23 This article has been roundly criticized for poor experimental design, which yielded 0.029 mg of methyl mercury per gram of powdered amalgam after 35 days of a complicated procedure. This is a fraction of the minimum safe level, 24 and it is highly unlikely that this process could occur in vivo. 24 There have been no reported symptoms of methyl mercury poisoning through the consumption of contaminated fish at exposure levels of 0.8 mg of methyl mercury per day for 5 years. 25 

Elemental Mercury

Silver-amalgam dental fillings contain approximately 50% elemental mercury. Thus elemental mercury is the major source of concern to both the dentist and patient. Elemental mercury is a liquid at room temperature. It has a high vapor pressure (.005 mg Hg at 37°C). Approximately 75% is absorbed through the lungs.26 Gastrointestinal absorption is low, with estimates of up to 10%. 27 Absorption is also minimal through the skin, although the precise level has not been determined. 22 Elemental mercury accumulates in the kidney and brain and is excreted in the urine, bile, and lungs. 22 Mercury’s toxicity is probably a result of its affinity for sulfhydryl groups on proteins, but the results of studies in vitro do not relate well to conditions in vivo where distribution and accumulation of elemental mercury ions varies immensely from one type of tissue to another. 22 Acute toxic exposures are rare. There have been cases of elemental mercury being accidentally released into the bloodstream, as when a rectal thermometer breaks or when several grams of mercury are intentionally swallowed, 28 without any reported adverse effects from the mercury. Chronic toxic exposure leads to a condition called erethism, characterized by insomnia, irritability, loss of memory, lack of self-control, timidity, drowsiness, depression, and eventual tremors. 22 

Both the Occupational Safety and Health Administration/” and the National Institute for Occupational Safety and Health’? give a threshold limit value of 50 µg/m3 of mercury vapor as a time-weighted average based on constant exposure of forty hours per week. The World Health Organization has adopted a recommended limit of 25 µg/m3. Clinically significant effects (erethism, intention tremor, and gingivitis) have not been reported at air concentrations below 100 µg Hg/m3. In comparison, the range of mercury in urine for populations with no identifiable source of mercury exposure is up to 20 µg/L.31 Clarkson estimates the total daily absorption for all forms of mercury to be 2.3 µg/day.32 

Mercury Vapor and Toxicity

Antiamalgam proponents allege that the amount of elemental mercury that “leaks” from silver fillings is sufficient to be a factor in developing, or the direct cause of, a host of diseases including, but not limited to, Alzheimer’s disease, multiple sclerosis, depression, chronic fatigue, and immune system dysfunction. Their allegations are unsubstantiated. 

Mercury from amalgam enters the body mostly from breathing mercury vapor and not from swallowing the mercury that dissolves in the saliva. The oral cavity is constantly wet due to the continuous secretion of saliva and the very high humidity of intraoral air. Since the absorption of mercury through the GI tract is minimal, the mercury from amalgam that is swallowed adds very little to the total body burden of mercury. 

Although people with amalgam fillings have higher oral levels of mercury vapor than do people without amalgams, the release of mercury appears to be sporadic rather than continuous, and is exacerbated by heavy chewing. Tests for intraoral mercury vapor are routinely performed after the subjects have vigorously chewed gum for up to ten minutes. The measurement techniques and results of different researchers have shown wide variation, from 10 µg Hg/m3 33-35 to 1. 7 µg Hg/m3.36-41 

Eggleston claimed that the mercury from amalgam reduced lymphocyte responses, thereby compromising immune function.42 This study was criticized because it wasn’t blinded and the author did not present a thorough review of his methodology. A subsequent and far better study of the effect of amalgam on three major populations of lymphocytes showed no indication that amalgams affect the human immune system.43 

Dental amalgam has also been accused of being a factor in the development of Alzheimer’s disease.44 But recent studies give compelling evidence that this is not true.45,46 Both studies involved evaluating people living under similar environmental conditions, in a nursing home45 and a monastery.46 The nuns in the monastery were 75 to 102 years old and had lived together for many years. Those with amalgam fillings were compared on eight different tests of cognitive function to those who did not have amalgam fillings. There were no differences. 

For years the American Dental Association (ADA) has collected data on the health, diseases, and causes of death of American dentists. The ADA has also run voluntary mercury-level tests at dental meetings. The results of these on-site screenings at the American Dental Association 1985 and 1986 annual meetings showed mean urinary values of 5.8 µg Hg/Land 7.6 µg Hg/L, respectively.t” Approximately 10% of the subjects had urinary mercury concentrations above 20 µg/L. This is in contrast with the general population, which has a mean urinary mercury concentration of 1 to 3 µg/L.48 It is logical that dentists who drill out and place amalgams would have higher mercury body burdens than would the general population. It also makes sense, therefore, to see if dentists have higher levels of disease or premature death. It is compelling evidence of the safety of amalgam fillings that dentists exhibit no higher levels of morbidity or mortality.49 Amalgam opponents rarely address these well-established findings. 

Boyd et al. claimed that sheep kidney function was dramatically damaged by mercury from amalgam fillings.50 Analysis of this study concludes that there was no damage because there were no pathological changes in the kidney, nor was there an increase in the blood urea nitrogen, which will ordinarily increase when there is an impaired glomerular filtration rate.51 In addition, Sandborgh-Englund et al.52 were unable to confirm the findings reported by Boyd et al. Ekstrand et al.51 found no effects on various parameters of kidney function in humans and concluded that sheep may not be appropriate models for testing the toxic effects of dental filling materials. 

In a study reported in the New York Times, Summers et al.53 reported a significant increase in the proportion of mercury-resistant bacteria present in the intestines of six monkeys after insertion and removal of amalgam fillings. They concluded that amalgams may contribute to the emergence of drug-resistant bacteria. Edlund et al. 54 retested this hypothesis with human subjects. They found that when their results were compared with the normal variations from a control group, they were not statistically significant. 54 

Allergy to any of the components of an amalgam does exist; there are also people who are hypersensitive to composite fillings, methylmethacrylate denture material, and even gold alloys. The allergic reaction to amalgam may be local or more widespread. The skin is the most common site and the reaction is often self-limiting and subsides within two or three weeks even without the removal of the filling.55 The proportion of people who are allergic to mercury has been shown to be under 1 %.56 

Daily Uptake of Mercury Through Inhalation and Ingestion

Determining the amount of mercury released and absorbed from amalgams is difficult. Olsson and Bergman57 have listed the following factors as variables affecting the amount of mercury released from amalgam fillings: number of teeth, number of surfaces, baseline mercury release, magnification factors such as eating or tooth brushing, eating habits, brushing habits, oral breathing habits, nose/mouth breathing ratio, inspiration/expiration ratio, swallowing, inhalation absorption, ingestion absorption, and body weight. In 1992 Olsson and Bergman, in an excellent study, arrived at a figure of 1 to 2 µg/day of mercury uptake for subjects with more than 8 amalgam fillings.57 Computational errors led many investigators to overestimate the amount of mercury that is released and absorbed during daily life. 

Mackert and Berglund58 pooled the data from studies where mercury release was monitored for more than 13 hours. Using the model designed by Olson and Bergman57 in which 25% of the total mercury released during a day was found to be released during oral respiration, they assumed that half of this 25% (12.5%) would be released during inspiration through the mouth. 

Mackert and Berglund also assumed that 80% of the 12.5% would be absorbed through the lungs, giving a 10% rate of absorption. The other 75% of the mercury is ingested. Ingested mercury must first be oxidized to be absorbed and the rate of absorption is assumed to be 7%. Thus the percentage of the released amount of mercury that is absorbed is 75% x 7% = 5.25%, or about 1.0 µg.58 

UNSCIENTIFIC SCREENING MEASURES 

Antiamalgam doctors often use an industrial-grade mercury detector. This device multiplies the tiny amount of mercury it actually detects by a factor of 8000 so that the reading will give the amount of mercury in a cubic meter of air. Human tidal volume is 0.5 liters27 and human inspiratory capacity is 2.8 to 4.3 liters, a volume far less than a cubic meter (1000 liters). In addition, the release of mercury from fillings is not continuous and much of the released mercury is exhaled, not inhaled. 

The electrical reading of fillings is done with a metering device similar to a common voltmeter. This device is purported to provide the data necessary to determine the sequence of removal of the amalgam fillings, with the “negative” fillings being removed before the “positive” fillings.1 But by simply reversing the probes, one gets exactly the opposite sequence. Marek states that this device actually records the “difference between the corrosion rate without that contact of two materials (the electrical probe and the amalgam) and with the contact of two materials.”59 

The US Food and Drug Administration (FDA) investigated one such device, the “Amalgameter.” In a 1985 regulatory letter to Hal Huggins, DDS, the inventor of this device, the FDA informed him that “the Amalgameter’s labeling recommended removal of dental fillings based on findings for which there was no scientific basis, and that it was promoted as a medical device for which there was no approval for manufacture or marketing.”60 

A symptom questionnaire is given that usually includes a general history and numerous specific questions concerning skin problems, nervous disorders, digestion, blood diseases, cancer, endocrine problems, and emotional problems, as well as feelings of malaise, tiredness, restlessness, boredom, and excitability, occurring now or in the past. The list is so inclusive that any healthy person would find it hard not to confirm the presence of at least some of the “telltale” symptoms. 

Huggins1 recommends hair analysis to determine the patient’s calcium, manganese, and mercury levels, as well as the levels of zinc and potassium. But “hair grows very slowly, so even samples taken close to the scalp may not reflect present bodily conditions.”61 Moreover, different laboratories reach different conclusions about the same hair samples62 and a normal range for minerals in the hair has not been established.63 Nor is it clearly understood how mineral content of the hair relates to mineral concentration in the blood and other tissues. Hair analysis may be of value in determining if an individual was exposed to a toxic element such as arsenic, chromium, or lead, but even then shampoos and hair dyes can distort the test results.61 

Some physicians and dentists charge for a skin patch test to determine “mercury allergy” or “hypersensitivity.” The reaction of the skin and the oral mucosa is often different. It is possible for the skin to be sensitized but not the oral mucosa, or there may be concurrent sensitization of both skin and mucosa, or the mucosa may be sensitized but not the skin (a rare occurrence).64 Interpretation of patch test results is difficult and requires expertise that only specially trained allergists have. And even in those cases where such expert allergists are consulted, there are numerous situations that can lead to false positive or false negative reactions.65 This makes patch testing for mercury allergy highly subjective and of little value. 

A Public Health Perspective

Amalgam fillings have restored billions of teeth in their 150-year history. Because of the ease with which they can be placed, their longevity, and their low cost, amalgams have been an unqualified public health success. But the economic foundation of dental practice has been adversely affected by fluoridation, which has led to a marked decrease in the amount of tooth decay, and by managed care, which has lowered reimbursement for many dentists. Some dentists’ greed and ignorance of the scientific facts, coupled with the media’s irresponsibility and lack of skeptical scrutiny, have encouraged a great many patients to have their silver fillings replaced in order to prevent or cure many diseases and conditions for which causes have not been scientifically discovered. Some of these patients have been seriously injured by these unnecessary treatments. In 1985 a $100 000 settlement was awarded a 55- year-old California woman whose fillings were removed because her dentist claimed they were a “liability” to her large intestine. The dentist caused severe damage to two teeth, leading to root canal therapy; two other teeth couldn’t be saved and had to be extracted. 66 

Because those opposed to amalgam haven’t been able to produce convincing scientific proof, they have turned to the courts and legislatures proposing that it be made a crime for dentists not to inform patients that silver fillings contain “poisonous mercury.” A few state legislatures have thus introduced resolutions that promote the mercury scare under the guise of “informed consent.” This is inappropriate because the doctrine of informed consent implies a proven danger, which is not the case. Two groups behind this misguided effort are Defense Against the Mercury Syndrome and the Foundation for Toxic-Free Dentistry. 

The strident call to ban amalgam is unique among potential environmental toxins. In the past, a specific disease or condition has been recognized in a population and these cases have been compared to a symptom-free control group in terms of exposure to possible causative agents. With amalgam, on the other hand, a wide range of diseases and conditions were attributed to it based solely on self-reported improvements in symptoms when the amalgams were removed. The data on the normal morbidity and mortality rates of dentists who have a proven higher body burden of mercury than the general public was ignored. Today we also have compelling data from groups with and without fillings who live in very similar environmental conditions and these, too, refute the claims of the antiamalgamists. 

Most data suggest that people with large numbers of amalgams do have a higher daily dose of mercury than do people with fewer or no amalgams. But there is convincing evidence that mercury levels many times higher than those associated with a mouthful of amalgams pose no risk of adverse health effects. Results of studies have also shown that the body’s mercury burden is highest immediately after placement or removal of amalgams. This information casts a critical light on those dentists, physicians, and patients who have claimed improvement of symptoms immediately following amalgam removal. 

The cardinal rule of toxicology is: “Only the dose makes a poison.” The overwhelming weight of scientific evidence is that the amount of mercury that may be released from silver-amalgam fillings is far below the threshold value that would pose any danger to adults or children. It must also be remembered that the political restraints placed on amalgam use in certain European countries are a response to a desire to lower the environmental impact of dental mercury waste released into the air and water rather than a response to any alleged dangers to patients with amalgams. 

The loss of such a useful and low-cost method of tooth repair would lead to a dental public health crisis. In 1993, Assistant Secretary for Health James Mason, MD, reaffirmed the PHS position that “there are no data to compel a change in the current use of dental amalgam.”67 This review supports Dr. Mason’s conclusion. 

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