303

Vol. 52, No. 5, Fall 1992

Mercury in Dental Amalgam-a

Public Health Concern?

Raymond A. Flanders, DDS, MPH Chief, Division of Dental Health Office of Community Health Illinois Department of Public Health 535 West Jefferson Street Springfield, IL 62761 Abstract

Dental amalgam has been the subject of intermi~ent controversy since it was introduced into dental practice approximately 150 years ago. The controversy has centered on the use of mercury in dental amalgam and the potential health implications to dental patients and dental health professionals from mercury exposure. In recent years the debate over the use of dental amalgam has intensified due to several articles in professionaljournals and media coverage by television and the press. This paperreviews the recent literature regarding dentalamalgam, describes the activities of the antiamalgamists, examines the alternatives to dental amalgam, and reviews the recommendations for additional research. The existing scientific evidence does not demonstrate that mercury in dental amalgamposes a public health hazard. However, researchers on both sides of the controversy agree that much remains to be examinedabout the health implications of dental amalgam and that the subject merits continued research. Key Words: dental amalgam, mercury, amalgam controversy, antiamalgamists,public health concern.

Dental amalgam has a long record of proven clinical performance as a restorative material in the practice of dentistry. Introduced into dental practice approximately 150 years ago, to this day, silver amalgam remains the most inexpensive, reliable, and most extensively used restorative material in dentistry for the repair of posterior teeth (1). Dental amalgam, prepared by dental staff just prior to its use, is composed of approximately equal weights of metallic mercury (in the form of mercury salts) and amalgam alloy (silver, copper, tin, and zinc) (1,2). It is this composition that has made dental amalgam the subject of intermittent controversy for many years. The debate has centered on the use of mercury in dental amalgam and the potential health hazards to dental patients and personnel from mercury exposure. In recent years the controversy over the use of mercury in dental Manuscriptreceived:9/23/91;retumedtoauthorforrevision: 11/7/91; accepted for publication: 2/3/92.

J Public Health Dent 1992;52(5):303-11

amalgam has intensified due to several articles in professional journals, and attention by television and the press. The purpose of this paper is to review the recent scientific literature regarding the use and safety of mercury in dental practice-in particular, the health implications of the use of dental amalgam. History of Dental Amalpam Controversy surrounding the use of amalgam was first recorded in 1833, when dental practitioners in the United States began using a primitive silver paste made of shavings from silver coins mixed with mercury (3,4). This restorative material had deleterious side effects that led to vigorous opposition to its use by the prevaiiing professional group of the day, the American Association of Dental Surgeons(4). This controversy, the first Amalgam War, was not resolved until the late 1800s when G. V. Black of Northwestern University developed a balanced and effective amalgam formula and demonstrated that amalgam was an acceptable restorative material. The specifications for mercury composition in dental amalgam were developed jointly in 1932 by the American Dental Association and the United States Bureau of Standards (3). The second Amalgam War began in 1920when Professor Alfred Stock, a German scientist, claimed that mercury could be absorbed into the body from dental amalgams and he expressed concern for the health of patients and dentists. Stock’s work was questioned and finally repudiated in 1934, and the amalgam controversy remained dormant until the late 1970s (3). In 1976 claims began to appear that mercury was released from amalgam restorations during brushing, chewing, and bruxing, resulting in mercury toxicity and, consequently, a wide range of neurologic, psychiatric, and immunologic diseases. These claims attracted a great deal of media attention and generated considerable professional controversy regarding their validity. Laboratory instruments had made it possible to measure the amount of mercury vapor released from amalgam restorationsduring removal, replacement, and after chewing (4). Although there was no evidence that these small amounts of mercury vapor were related to disease entities, several studies inferred that its accumulation in the tissues could

304

produce a variety of diseases. The controversy escalated even further in the 1990s when the national television program "60 Minutes" reported "miracle cures" for multiple sclerosis and other diseases after removal of dental amalgams. Also, studies from the University of Calgary reported mercury buildup in body tissues of sheep and monkeys as a result of mercury in dental amalgam. These events have gained the attention of the general public, various state legislative bodies, the American Dental Association, the Federal Drug Administration, the US Public Health Service, and groups opposed to dental amalgam. It appears these recent events have intensified the third Amalgam War, which began during the 1970s. Review of the Literature A critical review of the literature conducted by Langan and colleaguesconcluded that there is no evidence in the scientific literature to support the claim that mercury vapor released from amalgam restorations causes mercury toxicity. Langan reviewed the history of dental amalgam, the chemical forms and sources of mercury, exposure to mercury from all sources, biologic monitoring of mercury exposure, mercury toxicity, and allergic reactions to mercury and dental amalgam. The authors stated that allergic reactions to amalgam do occur and have been documented, but are extremely rare. The authors reaffirmed the safety of dental amalgam as well as the clinical benefit to the dental patient (3). In 1987, Enwonwu reviewed recent publications regarding potential health hazards associated with the release of mercury vapor from dental amalgam restorations. Enwonwu reported on the sources of the human body burden of mercury, the metabolic distribution of mercury vapor, and some reported findings of mercury toxicity in dentistry. The author documented evidence of the release of mercury vapor from amalgam restorations during tooth brushing, chewing and other oral activities. The author concluded, however, that there were no "unequivocally convincing" published studies that provided proof of a causal link between this source of mercury and any specific human health problem of significance. The author also recommended continued research in order to completeour knowledge of the metabolism of mercury vapor in humans (1). A review of the amalgam controversy by Mackert examined the claims of adverse health effects from amalgam restorations, the daily dose of mercury from amalgam, mercury allergy, and overnight "cures" alleged to have occurred after amalgam removal. The author concluded that the scientific evidence demonstrates that the contributionof dental amalgam to the daily body burden of mercury is minor, and no adverse health effects can be attributed to amalgam restorations. Mackert also pointed out that less than 1 percent of the general population show any clinical manifestation of allergy to dental amalgam (5). An assessment of the research by Mandel con-

Journal of Public Health Dentistry

cluded that dental amalgams "do not appear to pose a risk of kidney dysfunction, neurotoxicity, reduced immunocompetence, or pregnancy outcome." The author also stated that research on all dental materials is an ongoing professional responsibility, and he urged that epidemiologic studies relating amalgam exposure to health status be a high priority for the research community (6). In his review of the literature on the alleged health implications of dental amalgam, Molin discussed oral galvanism as it was reported in Scandinavia, and reported that no documented studies showed any connection between dental amalgam and oral galvanism (7). A study conducted by Mackert et al. determined the lymphocyte count in individuals with and without amalgam restorations (8). The purpose of the study was to examine the claims made by Eggleston and others that dental amalgam can adversely affect the percentage of T lymphocytesand thereby result in reduced immunocompetence (9). The authors examined the percentage of lymphocytes in 37 subjects-21 with amalgam restorations and 16 without. The study subjects, between the ages of 18 and 50, were selected to minimize the study effects of age-related changes in the immune system. Complete blood counts were conducted to obtain the total number of leucocytes and lymphocytes and the percent of leucocytes that were lymphocytes. The mean cell counts for the two groups were examined for each of the cell types and no statistically significant difference was found between the study subjects with amalgam restorations and the group of subjects without amalgam restorations. The results of the Mackert study demonstrated that amalgam restorations did not adversely reduce the level of lymphocytes, nor did they reduce human immunocompetence (8). Berglund conducted a study to determine the dose of intraoral mercury vapor released from dental amalgam during a 24-hour period. Fifteen subjects with at least nine occlusal amalgam restorations and five subjects without any amalgam restorations participated in the study. The subjectsfollowed a standardized schedule for 24 hours, eating and brushing their teeth at specified time intervals. The amount of mercury vapor released was measured by atomic absorption spectrophotometry. All of the amalgam restorations in the study subjects were more than a year old and none of the subjects was occupationally exposed to mercury. Samples of the subjects' urine and saliva were analyzed to obtain the values of mercury concentration and the rate of release of mercury into saliva. The daily release of mercury vapor from dental amalgam, after correction for oral-to-nasal breathing and for retention of expired air, was found to be about 1 percent of the dose obtained from a threshold limit value (TLV) exposure of 50 micrograms Hg/meter3 air. The author concluded that the amount of mercury vapor released from dental amalgam restorations made a small and insignificant contribution to the total body accumu-

Vol. 52, No. 5, Fall 1992

lation of mercury (10).This study pointed out the inaccuracy of the measurements reported by Vimy and Lorscheider of the University of Calgary (18,191. A study conducted by Olstad et al. sought to determine the effect of recently placed amalgam restorations on urinary mercury concentration. Nine children treated with occlusal amalgam restorations had urine samples examined before, during, and after the restorative treatment. The study results demonstrated that one single session of amalgam restorations did not represent a mercury exposure that was detectable in a longitudinal, individual study (11). Two studies completed by Fung et al. examined the levels of mercury and methyl mercury in patients at different time intervals after receiving dental amalgam restorations (12,131. In the earlier reported study (12),the authors determined the blood and urine levels of mercury and methyl mercury at different time intervals for one year after placement of amalgam restorations. The study involved 31 patients from the University of Nebraska College of Dentistry, none of whom was exposed to occupational or other unusual levels of mercury or methyl mercury. This study determined that unsafe levels of mercury could not be detected from old amalgam restorations or after placement of new restorations. Results of the other study (13), using a mercury analyzer with increased sensitivity, also indicated that patients were not subjected to unsafe levels of mercury or methyl mercury before or after amalgam placement. The authors concluded that mercury released from amalgam restorations is safe and is not a potential health hazard to patients. Snapp et al. determined the exposure to mercury from dental amalgam by comparing the blood levels of mercury before and after the removal of all amalgams from 10 study subjects. The subjects each had an average of 14 amalgam surfaces, which were removed in a single appointment. The use of the rubber dam during amalgam removal was left to the discretion of the clinician and was, therefore, not consistent. The level of blood mercury was obtained before the removal of amalgam restorations, and blood sampling continued after removal for five to 18 weeks. Study results demonstrated that the blood levels of mercury attributable to amalgam were well within the normal concentration of the general population. There have been no adverse health effectsattributed to that level of exposure; thus, the authors concluded,that the level of mercury exposure due to dental amalgam restorations does not pose any health threat (14). A study in Sweden conducted by Michel et al. examined the relation between symptoms of fatigue and dental amalgam and other psychosocial and disease factors. Thirty-nine female hospital workers were questioned regarding their health history, fatigue, smoking habits, and psychosocial factors. Information regarding the subjects’oral health and number of amalgam restorations

305

was obtained from their dental charts. The authors concluded that factors other than mercury released from dental amalgam could explain symptoms of fatigue (15). In another Swedish study, conducted by Ahlquist et al., the authors obtained health information from 1,024 dentulous women aged 38-72 who answered 30 specific questions regarding symptoms and complaints. The answers to these health questions were then related to the number of tooth surfaceswith amalgam restorations.The survey results showed no positive correlations between the number of symptoms and the number of amalgam restorations. The authors concluded that the results of this study did not support the claim that existing amalgam restorations should be removed from patients (16). Naleway et al. conducted a study in 1985 and 1986 as part of the health screening program at the annual meetingsof the American Dental Association to determine the relationship between elevated urinary mercury levels and kidney dysfunction. Approximately 10percent of the dentists had elevated mercury levels. The authors, using specific criteria of kidney dysfunction, could not find a statistical association between kidney dysfunction and elevated urine mercury exposure from occupational, food, and amalgam sources (17). During the past 10 years, technical advancements in mercury detection equipment have allowed investigators to identify minute amounts of mercury vapor. Studies conducted by Vimy and Lorscheider estimated the cumulative amount of mercury vapor inhaled by an individual with approximately nine occlusal amalgam restorations over a l@year period to be 73 mg, or 0.85 percent of the total mercury available in the restoration. This estimate was based on an average occlusal restoration of two grams containing 50 percent mercury by weight, and a daily inhalation of approximately 20 nanograms of mercury from the amalgam restoration. They measured mercury vapor levels in intraoral air in 35 subjects with varying numbers of amalgam restorations. The subjects followed a specific eating and snacking daily routine, and measurements of mercury vapor were taken at specific time intervals. The authors concluded that after chewing activity, mercury vapor levels in subjects with amalgam restorations increased 54 times over the basal level of those without amalgam restorations (18,191. Their results have since been shown by Mackert to have serious methodologcal flaws that produced estimates of mercury vapor to be at least 16 times too high (20). Hahn et al. of the Universityof Calgary then conducted a study to determine possible uptake routes and distribution of mercury vapor into various body tissues. The authors placed amalgam restorations in 12 molar teeth (three molars on each side of the upper and lower jaw) of a four-year-old sheep. The incorporation of radioactive mercury in the dental amalgam allowed the authors to measure the amount of mercury uptake in various body

306

tissues. The authors concluded that mercury was localized in the kidneys and liver, and amalgam restorations were a source of chronic mercury exposure (21).Vimy et al. conducted a study on sheep to determine the maternal-fetal distribution of mercury released from dental amalgam restorations. The authors placed 12 occlusal amalgam restorations containing radioactive mercury in five pregnant sheep. Samples of blood, amniotic fluid, feces, and urine were collected at one- to three-day intervals for 16 days after amalgam placement. The tissue specimens were analyzed for radioactivity and total mercury concentrations were calculated. Study results indicated that mercury from dental amalgam was present in maternal and fetal blood and amniotic fluid within two days after placement of dental amalgam restorations and that mercury was present in all tissues examined. The authors concluded that the mercury released from amalgam restorations accumulates in maternal and fetal tissues soon after amalgam placement and that it progresses at a steady rate with advancing gestation (22). The Calgary Group also conducted a study to determine the distribution of mercury released into monkey tissues from amalgam restorations. The authors placed amalgam restorations, using radioactive mercury as an amalgam component, in 16 teeth (three molars and adjacent second premolar in each quadrant) of one monkey. Approximately one month afteramalgam placement, the blood, urine, and tissue samples were examined. The authors stated that radioactive mercury was present in various organs and tissues as a result of dental amalgam, and they concluded that dental amalgam was not a stable tooth restorative material (23). These studies have received considerable media and professional attention. However, since their release and publication, these studies have been shown to be methodologically flawed (2,5). Each of the studies conducted by the Vimy and Lorscheider group contained small numbers of animals, smaller numbers of animal controls, and none of the studies had positive controls (21. The dental amalgams placed in the study were weak and easily abraded, and most of the mercury was found in the gastrointestinal tract and feces, which demonstrates that mercury was released by abrasion and not by volatilization as the authors asserted (2). The study also utilized intraoral measurements of mercury vapor, which have been shown to be inaccurate (2,8). Antiamalgamists Dr. Hal Huggins, a Colorado dentist, is one of the leaders of the antiamalgam movement. According to Consumer Reports (24), Dr. Huggins’ interest in the subject of mercury in dental amalgam began during his conversations with a Brazilian scientist, Dr. Olympio Pinto. Dr. Pinto, whose father was a dentist, convinced Dr. Huggins of the potential harmful effects of mercury in dental amalgam restorations. In ”It’s All in Your Head,” Dr.

Journal of Public Health Dentistry

Huggins lists the diseases he claims may be caused by mercury toxicity resulting from the placement of dental amalgam fillings. These diseases include multiple sclerosis, epilepsy, leukemia, Hodgkin’s disease, arthritis, mononucleosis, premenstrual syndrome, and depression. Dr. Huggms also describes his treatment procedures and successes, which include an amalgameter (to measure electric current in each restoration), removal of highly charged negative restorations, and special nutritional supplements “to rid the body of stored mercury” that has accumulated as a side effect of dental amalgam restorations. Dr. Huggins claims to have been studying mercury toxicity since 1973 and, although he has made many claims regarding mercury toxicity and amalgam restorations, none of these claims is substantiated, nor has he completed clinical studies to support his claims (24). Other prominent antiamalgamists include Michael Ziff, an Orlando, Florida, dentist, who travels around the country presenting courses on mercury toxicity. Dr. Ziff‘s father, Sam Ziff, is editor of the newsletter Bio-Probe, which is published bimonthly from their offices in Orlando. Mr. Sam Ziff, author of the book “Silver Dental Fillings: The Toxic Time Bomb,” has also coauthored a booklet with his son, Dr. Michael Ziff, ”The Hazards of Silver/Mercury Dental Fillings.” The Ziff s distribute this literature during their presentations and also to antiamalgam dentists, who give this information to their patients (24). Those opposed to dental amalgam claim that the mercury, allegedly vaporizing from amalgam restorations, causes myriad diseases. As noted in all of the statements on dental amalgam made by the major national health organizations in the United States, there is no scientifically sound evidence linking mercury in dental amalgam to adverse health effects in human beings. Other statements by antiamalgamists include claims that amalgam contains free mercury, that mercury vapor escapes in large quantities from amalgam, that intraoral mercury vapor can be measured accurately by hand-held meters, and that all released mercury vapor is inspired. All of these statements have been shown to be false or misleading, according to statements issued by all national health organizations and by recent well-documented studies (2). There are national and local antiamalgam organizations that hold regular meetings and disseminate information regarding their views on dental amalgam. The International Academy of Oral Medicine and Toxicology (IAOMT) holds annual scientific sessions. The IAOMT also holds regional meetings, and both annual and regional meetings feature health professionals who hold and present antiamalgam views. Often very persuasive in their arguments, these groups are similar in many ways to the antifluoridation groups. Each group claims that virtually all diseases can be traced to mercury in

Vol. 52, No. 5, Fall 1992

dental amalgam or to fluoride in the drinking water. These groups also claim to present evidence based on epidemiologically sound data. These claims, however, are often false and /or misleading, and the data presented as sound are often derived from seriously flawed scientific studies. In Illinois, an antiamalgam group called Dental Amalgam Mercury Syndrome (DAMS), founded by Louise E. Herbeck, actively lobbies the Illinois legislature regardingdental amalgam. Ms. Herbeck has collected hundreds of case histories from individuals who claim to suffer from chronic mercury poisoning directly caused by the mercury in dental amalgam restorations. Unsubstantiated claims from large numbers of patients claiming systemic effects from dental amalgam have also been made by Huggins (25). However, as noted by Baratz (21, most of these patients ... had easily explained systemic illnesses such as diabetes mellitus, lupus erythematosus, or degenerative joint disease and they improved with accepted treatments. Some had somatiform disorders characterized by inconsistent symptoms, tests and physical findings. Others had allergic responses which could be objectively determined and confirmed. Some of the allergic responses were not easily discerned and required considerable testing to a variety of agents. Some had no medical illness.

Dr. Baratz, a dentist who is also a physician and scientist (faculty member in the Department of Oral Pathology, Tufts University, School of Dental Medicine, and staff member at Department of Medicine and Surgery, Veterans Administration Hospital, Boston, Massachusetts), concluded that without proper medical training, or a careful differential diagnosis, one can be very easily mislead, and this is the basis for most false claims regarding adverse health effects of dental amalgam (2). DAMS, also known as Defense Against Mercury and Silver, is the sponsoring agency behind the introduction of much of the antiamalgam legislation in several states, most currently in Alaska, California, Illinois, Michigan, Nevada, and New Mexico. Legislation introduced in Nevada and New Mexico would have banned the use of dental amalgam in those states. The New Mexico Dental Associationwas instrumental in defeating this legislation and in Nevada, a Senate committee recommended that the pending legislation not pass. In Alaska, legislation failed that would have required dentists to obtain written informed consent from patients prior to placing amalgam restorations. This legislation would also have required dentists to describe restorative materials to be used, possible harmful effects, available alternatives to amalgam, and potential risks associated with the alternatives. Legislation was introduced in California that would require the dentist to obtain informed consent before placing an amalgam restoration. The Californialegislation, as of this

307

writing, is still in committee and not expected to pass. Legislation in Michigan, also in committee, would make dentists liable for any adverse health effects resulting from the use of dental amalgam. In Illinois, legislation was adopted calling upon the Illinois Department of Public Health to conduct a review of the literature on the health implications of dental amalgam restorations. This legislation requests the Department of Public Health to report its findings to the state legislature by September 1991 (26). Statements on Dental Amalgam American Dental Association. After review of the literature, Langan et al. stated the position on dental amalgam of the American Dental Association (ADA). The ADA position stated there is no evidence in the scientific literature that mercury vapor released from dental amalgam restorations causes mercury poisoning. Allergic reactions to amalgam have been documented, but are extremely rare. Finally, dental amalgam has an excellent record of safety and benefit for over 100years (3). In March 1991, the American Dental Association released the following statement regarding dental amalgam (27): Amalgam restorations are safe and pose no acute or chronic risks to the American people. Recent studies purporting to link pathologic conditions with placement of amalgam are flawed in methodology and conclusion, and do not warrant concern about amalgam safety. The ADA believes that current restoration practices may be continued safely. The ADA urges further research on amalgam safety by the National Institute of Dental Research (NIDR), other agencies within the Department of Health and Human services, and industry and academia. ADA pledges to assist NIDR inobtaining sufficient appropriations to fund additional research.

Food and Drug Administration. On March 15,1991, the United States Food and Drug Administration (FDA) convened the Dental Products Panel to discuss the classification of dental amalgam. The purpose of the panel meeting was to review past and current evidence regarding dental amalgam, to determine if that evidence warrants the need for further research, and if so, determine what kinds of research are needed to answer the questions of amalgam safety. The FDA statement on dental amalgam in March 1991 stressed that current data are not sufficient to demonstrate that mercury fromdental amalgam poses a health risk to patients. The FDA stated that 'Ithere are neither controlled studies in humans, nor a conclusivebody of clinical evidence, demonstrating that

308

mercury amalgam fillings cause any known disease." The FDA advised that persons with amalgam restorations should not have them removed either to prevent adverse health outcomes or to try to reverse the course of existing disease (28). National Institute of Dental Research. The National Institute of Dental Research (NIDR), National Institutes of Health, supports and conducts research on a wide variety of oral diseases and conditions and dental restorative materials. A major area of NIDR investigation during the past five years has been related to the safety of dental amalgam restorations. The NIDR statement on dental amalgam as of March 1991 stressed that research to that date has not proved that mercury released from dental amalgam is harmful except to those rare individuals who are hypersensitive to mercury. There is no sound scientificevidence linking mercury in dental amalgam to multiple sclerosis, arthritis, mental disorders, or other diseases, and there have been no controlled studies that demonstrate adverse health effects attributed to dental amalgam restorations. The NIDR concluded that dental amalgams pose no known health risk to individuals who are not hypersensitive to mercury. The NIDR further stated that there is no reason for recommending either the discontinuation of dental amalgam as a restorative material or the removal of those restorations from patients who are not allergic to mercury or other componentsof amalgam (29). United States Public Health Service. The United States Public Health Service issued the following interim statement on dental amalgam at the FDA Dental Panel Conferenceon March 15,1991 (30): At present and until additional information under study dictates, there are no data that would compel a change in the current use of amalgams. When dentists are placing amalgams in teeth or removing amalgams, they should carefully adhere to guidelines developed for their use, and, to the extent possible, limit exposure to mercury.

The United States Public Health Service is currently conducting a comprehensive review of the literature regarding the health implications of dental amalgam. Dr. James0.Mason, Assistant Secretary for Health, Department of Health and Human Services, has appointed Dr. Harald Loe, director of the National Institute of Dental Research, and Dr. Vernon Houch, director of the Center for Environmental Control, Centers for Disease Control, as committee chairmen to conduct the study of dental amalgam. This benefit and risk assessment of amalgam is being carried out by the Committee to Coordinate Environmental Health and Related Programs. Dr. Harald Loe is chairman of the subcommittee charged to review the benefits of dental amalgam, and Dr. Houch is chairman of the subcommittee assigned to conduct a risk assessment of dental amalgam. As of this writing, these

Journal of Public Health Dentistry

committeeshave completed their respective reviews and have submitted them to the Deputy Director of the Food and Drug Administration for final review. The results of this literature assessment should be completed in 1992. National Institutes of Health Technology Assessment Conference.The "Effectsand Side Effectsof Dental Restorative Materials" conference held in August 1991 was sponsored by the National Institute of Dental Research and the NIH Office of Medical Applications of Research. The purpose of the conference was to review the literature regarding dental restorative materials, determine the prevalence and severity of side effects associated with dental restorative materials, and to recommend future directions of research on these materials. The conference panel, after testimony and review of the literature, issued the following conference statement: Current dental restorative materials are effective for restoring teeth for functional or esthetic reasons. Virtually all restorative materials have components with potential health risks. However, there is no scientific evidence that currently used restorative materials cause significant side effects.Availabledata donot justify discontinuingtheuse of any currently available dental restorative materials or recommending their replacement. Although mercury vapor is released from dental amalgam, the quantities released are very small and do not cause verifiable adverse effects on human beings.

Regarding dental amalgam, the conference panel concluded that there are no convincing data linking any specific disease to the body burden of mercury attributable to dental amalgam. The expert panel further stated that "the degree of exposure to mercury via dental amalgam is insufficient to be considered a health risk in virtually all individuals" (31). National Multiple Sclerosis Society. In a letter to the Dental Products Panel of the Food and Drug Administration on March 12, 1991, the National Multiple Sclerosis Society stated that their Medical Advisory Board had found "no sound epidemiologic evidence relating dental amalgam restorations to multiple sclerosis,and no sound clinical evidence suggesting that replacing dental amalgams leads to improvement in multiple sclerosis patients" (32). Consumers Union. Consumers Union (CU),publisher of Consumer Reports, is a nonprofit organization established in 1936 whose purpose is to provide consumers with information and advice on a wide variety of consumer goods and services, including health care. In a 1986 article in Consumer Reports on dental amalgam, CU stated that "except for a few people with a genuine allergy to mercury, CU knows of no one who's been harmed by dental amalgam " (24). The December 1990 broadcast of CBSTV's "60 Minutes," suggesting that mercury in amalgam restorations caused a variety of diseases and that their removal may result in overnight

Vol. 52, No. 5, Fall 1992

cures of systemic disease, and the strong public reaction and concern raised as a result of this television show, prompted a second article in Consumer Reports on the safety of dental amalgam. The article reviewed past and current literature, the antiamalgam challenge, OSHA guidelines, alternatives to dental amalgam, and safety of amalgam restorations. In 1991 Consumer Reports reaffirmed its previous statement that dental amalgams cause noadverse health effectsas supported by well-documented, sound epidemiologic research (33). Discussion The current amalgam controversy began during the early 1980s, when sensitive new measurement techniques enabled investigators to detect minute amounts of mercury vapor released from amalgam restorations. The prevailing belief prior to that time was that once the amalgam hardened, there was no release of mercury vapor from restorations. The question in the amalgam debate is whether trace amounts of mercury vapor that may be released from amalgam restorations have any health implications for those who receive restorations. A review of the recent literature, which includes several well-documented studies, demonstrates that the only documented health effect associated with amalgams is the rare case of mercury allergy (2,3,8,10-13).An allergic response to an amalgam restoration is usually a local reaction and often improves without intervention. It is estimated that less than 1 percent of the population is hypersensitive to dental amalgam (3). The Occupational Safety and Health Administration (OSHA) sets standards of mercury vapor concentrations by which even the most sensitive industrial workers can be chronically exposed without suffering adverse health effects. OSHA guidelines state that 300 to 500 micrograms per day is the maximum safe occupational exposure. Individuals with a moderate to large number of amalgam restorations are exposed to approximately one to three micrograms of mercury vapor per day, which is barely 1 percent of the dose considered safe (33). All of the recent literature indicates that dental amalgams contribute far less mercury to our total body burden than levels at which adverse health effects are noted. There is also no documented evidence that even potentially vulnerable populations, such as pregnant women and young children, are at any health risk from the trace amounts of mercury vapor that may be released from amalgam restorations (33). The antiamalgamists have pointed out that the mercury vapor detector provides "scientific" evidence that unacceptable levels of mercury vapor are present in the mouth. However, the mercury detector is designed to measure mercury vapor in the workplace, not in the mouth. The mercury detector, if used in the mouth, measures a small volume of air and multiplies the mercury level to estimate the amount of mercury vapor in a cubic

309

meter of air (33).This method of detecting mercury vapor often leads to inaccurate and misleading results. The levels of mercury vapor emanating from amalgams as reported in different studies also varies greatly, as have the methods of measurement. The extrapolation of these data are not uniform, which makes interpretation of the data and comparison between studies difficult if not impossible (3). Detection of the amount of mercury absorbed and its concentration and location in the body has long relied on biological monitoring (3). These methods provide reliable indicators of the absorbed dose and its location, and can be used to measure exposure from various sources of mercury. It has been shown that the mercury concentration in the blood and urine of persons with amalgam restorations is substantially less than the lowest concentration of mercury reported to cause adverse health effects (3). As previously noted, the only documented health effect associated with dental amalgam is the allergic response, which is usually manifested locally. A thorough review of allergic responses to amalgam restorations published in 1986 reported fewer than 50 documented cases of hypersensitivity to dental amalgam (3). As approximately 100 million amalgam restorations are placed each year in the United States (34),clearly allergc response to amalgam restorations is extremely rare. The potential for mercury exposure is present in the dental office and can occur either through direct skin contact or through the inhalation of mercury vapor. The American Dental Association periodically publishes recommendations and techniques that dental personnel should follow to maintain proper mercury hygiene practices in their offices (3,35). Dental personnel have higher exposure rates than the general population, yet dentists and dental auxiliaries do not demonstrate any adverse health effects related to mercury exposure. The ADA has sponsored a mercury testing service since 1982, which measures urine mercury levels in dentists and dental auxiliaries. The average levels found in dental professionals are higher than in the general population, yet they are well within the acceptable range (33). Researchers on both sides of the amalgam controversy agree that much remains to be learned about the potential health risks of dental amalgam. There is a lack of longterm epidemiologic data on the biologic mechanism of mercury in dental amalgam and on its manifestation in human populations. Additional research is needed to resolve the questions surrounding the amalgam controversy and to provide the public and the profession with a complete sense of security. This research should be interdisciplinary and collaborative, involving expertise from many disciplines, including toxicology, epidemiology, statistics, dentistry, medicine, and the behavioral sciences (36). Brown has reviewed the various research designs and the advantages and disadvantages of their application to obtaining appropriate data on dental amal-

Journal of Public Health Dentistry

310

gam. He concludes that a broad research agenda is needed and should include both in vitro research and animal studies. The type of data that can be collected when studying human populations should indicate the design of the research (36). Future research should also involve the development of stable amalgam systems that reduce the potential for mercury exposure, involve improvements in the clinical performance of dental amalgams, and include studies on the durability and potential toxicity of alternative restorative materials. The dental profession and other health agencies will continue to examine the safety and clinical effectiveness of dental amalgamand other restorative materials. In the meantime, the use of dental amalgam as a restorative material continues to decline. In the United States, the number of dental amalgams placed has declined by 38 percent in the last 11 years (34). From 1979 to 1990 the number of dental amalgams placed has gone from 157 million to approximately 96 million (34). As current restorative materials are developed, this decline in the use of amalgam will certainly continue. Newman compared alternatives to dental amalgam according to esthetics, prognosis, biocompatibility, technique sensitivity, and cost. The author recommended glass ionomer or composite for nonocclusalrestorations; composite inlay or direct composite for small occlusal restorations (class I or class 111, and gold or ceramic onlay (with caution) for large occlusally functioning restorations (37).All of these alternatives to amalgam range between two and six times the cost of an amalgam restoration, most of them are more technique sensitive, and some do not have the durability of dental amalgam. Although there are many alternatives to dental amalgam, the versatility of this restorative material is the main reason that amalgam continues to survive as the primary restorative material in dentistry.

Conclusions Dental amalgam has a 150-year history of successful clinical use. During that time, however, the issue of the safety of dental amalgam has been raised more than once. The controversy surrounding amalgam has centered on the possible toxicity of mercury vapor released from dental amalgam restorations. The scientific literature regarding the possible toxicity of mercury from amalgam restorations has been reviewed by many investigators. On the basis of these reviews and current scientific information, there is no sound evidence that dental amalgam restorations pose any health risk to any individual who is not allergic to the material, and the occurrence of mercury allergy is extremely rare. There is a need for additional research to resolve the unanswered questions regarding the health implications of dental amalgam. This research should include epidemiologic studies that relate the health status of large cohorts of patients to their exposure to dental amalgam. Future research should also include the development of stable amalgam systems and

studies involving the durability and safety of alternative restorative materials.

References 1. Enwonwu CO. Potential health hazard of use of mercury in dentistry: critical review of the literature. Environ Res 1987;42:257-74. 2. Barratz RS. Report on dental amalgam before dental products panel, US Food and Drug Administration. Washington, DC, Mar 15,1991. Dental products panel transcript. Washington, DC: Miller Reporting Company, 1991. 3. Langan DC, Fan PL, IIoos AA. The use of mercury in dentistry: a critical review of the recent literature. J Am Dent Assoc 1987 Dec;l15:867-80. 4.Mandel ID. Living with amalgam: an environmental perspective. Quintessence Int 1991 May;22(5):337-9. 5. Mackert JR. Dental amalgam and mercury. J Am Dent Assoc 1991 Aug;l22:5461. 6. Mandel ID. Amalgam hazards: an assessment of research. J Am Dent Assoc 1991Aug;122:62-5. 7. Molin C. Oral galvanism in Sweden. J Am Dent Assoc 1990 A~g;l21:281-4. 8. Mackert JR, LeffellMS, Wagner DA, Powell RJ. Lymphocyte levels in subjects with and without amalgam restorations. J Am Dent Assoc 1991 Mar;122:49-53. 9. Eggleston DW. Effect of dental amalgam and nickel alloys on T lymphocytes: preliminary report. J Prosthet Dent 1984;51:617-23. 10. Berglund A. Estimation by a 24-hour study of the daily dose of intra-oral mercury vapor inhaled after release from dental amalgam. J Dent Rcs 1990;69(30):364~51. 11. OlstadML, Holland Rl, Pettersen AH. Effect of placement of amalgam restorations on urinary mercury concentration. J Dent Res 1990;69(9):1607-9. 12. Fung YK, Molvar MP, Strom A, Schneider NR, Carlson MS. In vivo mercury and methyl mercury levels in patients with amalgam restorations. Gen Dent 1990Jan-Feb368. 13. Fung YK, Molvar MP, Strom A, Schneider NR, Carlson MS. In vivo mercury andmeth yl mercury levels in patients at hfferent intervals after amalgam restorations. Northwest Dent 1991 May-Jun; 7@3):23-6. 14. Snapp KR, Boyer DB, Peterson LC, Svare CW. The contribution of dental amalgam to mercury in blood. J Dent Res 1989;68(5):780-5. 15. Michel I, Norback D, Edling C. An epidemiologic study of the relation between symptoms of fatigue, dental amalgam and other factors. Swed Dent J 1989;13.33-8. 16. Ahlquist M, Bengtsson C, Furunes B, Hollender L, Lapidus L. Number of amalgam tooth f i h g s in relation to subjectively experiencedsymptomsina study of Swedish women. Community Dent Oral Epidemiol1988 Aug;16(4):227-31. 17. Naleway CA, Roxe D, Chou HN, Muller T, Dabney J, Siddoqui F. On-site screening for urinary Hg concentrations and correlation with glomerular and renal tubular function. J Public Health Dent 1991;51: 12-17. 18. Vimy MJ, Lorscheider FL. Intraoral air mercury released from dental amalgam. J Dent Res 1985;64:1069-71. 19. Vimy MJ, Lorscheider FL. Serial measurements of intraoral air mercury: estimation of daily dose from dental amalgam. J Dent Res 1985;64:1072-5. 20. Mackert JR. Factors affecting the estimation of dental amalgam mercury exposure from measurements of mercury vapor levels in intraoral and expired air. J Dent Res 1987 Dec;661775-80. 21. Hahn LJ, Kloiber R, Vimy MJ, Takahashi Y, Lorscheider FL. Dental "silver" tooth fillings: a source of mercury exposure revealed by whole body imagescan and tissue analysis. FASEB J 19903:264-6. 22. Vimy MI, Takahashi Y, Lorscheider FL. Maternal-fetal distribution of mercury released from dental amalgam fillings. Am J Physiol 1990Apr;258(4):93945. 23. Hahn LJ, Kloiber R,Leininger RW, Vimy MJ, Lorscheider FL. Whole body imaging of the distribution of mercury released from dental fillings into monkey tissues. FASEB J 1990;4325&60. 24. The mercury scare. Consumer Reports 1986Mar;51(3):150-2. 25. Huggins H. NIDR workshop: biocompatibility of metals in dentistry. ] Am Dent Assoc 1984Sept;109:469-71. 26. American Dental Association. States astir over AIDS, amalgam. J Am Dent Assoc 1991 Aug;122:107-8, 27. American Dental Assodation. Report on dental amalgam before

Vol. 52, No. 5, Fall 1992 Dental products panel, US Food and Drug Administration. Washington, DC, Mar 15,1991. Dental products panel transcript. Washington, DC: Miller Reporting Company, 1991. 28. Food and Drug Administration. Report on dental amalgam before Dental products panel, US Food and Drug Administration. Washington, DC, Mar 15,1991. Dental products panel transcript. Washington, D C Miller Reporting Company, 1991. 29. National Institute of Dental Research. Report on dental amalgam before Dental Products Panel, US Food and Drug Administration. Washington, DC,Mar 15, 1991. Dental Products Panel transcript. Washington, DC: Miller Reporting Company, 1991. 30. US Public Health Service. Report on dental amalgam before Dental products panel, US Food and Drug Administration. Washington, DC, Mar 15,1991. Dental products panel transcript. Washington, D C Miller Reporting Company, 1991. 31. US Public IIealth Service. Effects and side effects of dental restor-

311 ative materials. Technology assessment conference statement, National Institutes of Health. Aug 2628,1991. Bethesda, MD: Office of Medical Application and Research, Nl€I, 1991. 32. National Multiple Sclerosis Soatey. Report on dental amalgam before Dental products panel, US Food and Drug Administration. Washington, DC,Mar 15,1991. Dental products panel transcript. Washington, DC:Miller Reporting Company, 1991. 33. The mercury in your mouth. Consumer Reports 1991;56(5):316-19. 34. Nash KD, Bentley JE. Is restorative dentistry on its way out? J Am Dent Assoc 1991 Aug;122:79-80. 35. American Dental Association. Mercury hygiene: summary of recommendations in 1990.J Am Dent Assoc 1991 Aug;122112. 36. Brown LJ. Dental amalgam: designs for research in human populations. J Am Dent Assoc 1991 Aug;l22:73-7. 37. NewmanSM. Amalgamalternatives: whatcancompete?JAm Dent Assoc 1991 Aup,;122:67-71.