Is Mercury Amalgam Safe
for Dental Fillings?Michael D. Martin
Timothy A. DeRouen
Brian G. Leroux
Mercury amalgam is the most common, yet still controversial, treatment for dental caries. UW researchers hope to answer questions about safety by studying the health effects in a population of Portugese school children.Mercury is a toxic substance banned from most medical uses. Nevertheless, mercury-containing dental amalgam is ubiquitous as a common medical treatment for dental caries. Although its safety has been questioned for more than 150 years, a lack of scientific evidence renders answers elusive. A new University of Washington study may shed some light on this important public health concern. Elemental mercury mixed with elemental silver may have been used to repair teeth as early as the seventh century, according to an obscure reference in the Chinese Materia Medica of Su Kung, dated 659 A.D. In the 1830s, dentists in New York City began using the first commercial amalgam, known as "Royal Mineral Succedaneum." Scientific dentistry was new then, and the importance of careful removal of dental caries prior to the placement of a filling was unknown. As a consequence, these fillings were often unsuccessful.
By 1845 the American Society of Dental Surgeons, an early professional organization, passed a resolution condemning the use of mercury amalgam as a toxic substance, and expelled members who practiced such use.
When used properly, however, the material was long-lasting and relatively easy to manipulate. Eventually, in the late 1890s, largely through the work of Dr. G.V Black, the "father of modern dentistry," the formulation and proper application of mercury amalgam became better standardized and more successful. The material, with an elemental mercury content of approximately 50%, was widely accepted.
In the 1920s, Albert Stock, a German chemist, published a lengthy work in which he made several incendiary claims concerning negative health effects of mercury amalgam. His claims served to polarize debate between pro and anti-amalgam groups, and to touch off the second phase of the "Amalgam Wars." Although Stock later recanted most of his claims, the doubts about mercury amalgam were reinforced among the anti-amalgam forces.
The U.S. Bureau of Standards in 1932 issued the first "official" specifications for silver-mercury amalgam, which again became the standard material for restoration of carious teeth. Its use has spread throughout the developed world, and hundreds of millions of amalgam fillings are placed each year. It is generally recognized that no other material handles as well and lasts as long. The use of alternative materials may result in more secondary decay around restored teeth and the need for more frequent replacement of restorations. Thus, elimination of mercury amalgam would likely be costly economically and in terms of general oral health.
Amalgam Wars: Phase 3
Mercury's toxic effects on human beings vary with the form and route of exposure. The fate of mercury in the body, although extensively investigated, remains somewhat unknown. Target organs for elemental mercury include the kidneys and the central nervous system, and even low-level occupational exposure may have deleterious effects (Figure 1). Over the past decade critics of mercury amalgam have become ever more vocal.
Figure 1: Signs and symptoms of mercury toxicity
We are now, in a sense, in the middle of phase three of the "Amalgam Wars." One stimulus was a recent study of sheep. Mercury from fillings placed in their teeth migrated to the brain, kidneys, and other body tissues. Mercury amalgam proponents protested that sheep were not appropriate animal models. Contributing to the fray are both professional and lay "anti-amalgam" advocacy groups, publications devoted to halting the use of mercury amalgam as a treatment, and a World Wide Web site for the exchange of information. In the early 1990s, "60 Minutes" aroused further public concern with a segment titled "Poison in Your Mouth?" Opponents of mercury amalgam claim it causes a wide variety of ills from multiple sclerosis to an increased need to use tobacco. Several governmental and professional association panels and study groups have addressed questions concerning amalgam safety In general, they have concluded that although there is no scientific evidence that exposure to mercury amalgam as a dental treatment results in harmful health effects, further study is warranted. This view is similar to the position taken by the American Dental Association.
No adequate safety studies have been performed. Mercury amalgam's presumed safety is based on the lack of consistently noted deleterious effects for this commonly used treatment. In response to the increasing number of calls for safety studies, however, and in recognition of the lack of carefully designed and executed controlled clinical trials, the National Institute of Dental Research (NIDR) in 1995 announced a Request For Applications (RFA) to conduct a longitudinal, controlled clinical trial to determine the safety of mercury amalgam as a treatment. NIDR has proposed that children be studied because they are thought to be more susceptible to the neurobehavioral effects of mercury intoxication and would be more likely to show an effect if there is one. The project would require a truly interdisciplinary approach.
UW Awarded Grant
The University of Washington School of Dentistry in collaboration with the School of Public Health and Community Medicine and the University of Lisbon School of Dentistry responded to the RFA, and was awarded a $4.1 million grant to begin a clinical trial. We assembled a team of University of Washington faculty to develop the proposal, including Jacqueline Farwell (Neurology), Gail Rosenbaum (Psychometry), Brenda Townes (Psychiatry and Behavioral Sciences), Sandra Watkins (Pediatric Nephrology), and James Woods (Toxicology).The general idea of the study is to randomly assign subjects who have had little or no exposure to previous dental treatment to one of two treatment groups. The first group will receive mercury-containing amalgam fillings in all back teeth where needed, and tooth-colored "composite" resin fillings in front teeth where needed. The second group will receive only composite resin fillings in all teeth where needed. Both treatment regimens are considered acceptable, although the use of silver-mercury amalgam fillings is far more prevalent. The subjects will be tested for renal, neurological, and neurobehavioral function prior to and at intervals after dental treatment.
The ideal study population of children would have several important features. First, the need for dental fillings would be great. Second, the subjects should have little, or preferably, no previous exposure to mercury, including that from dental fillings. Third, the subjects need to be geographically stable, as the follow-up period is anticipated to be at least five years. The more culturally and socially homogeneous the population the better. A large population of children meeting these requirements is difficult to find in North America. Declining decay rates, increased access to dental care, and the high degree of mobility of families today all work against identifying a suitable population in the United States. Thus, we have chosen to study Portugese children in a setting where previous collaborative efforts have shown us that an ideal study population exists.
"You can prick my finger for a blood sample, but I don't want to look," seems to be the reaction of a young participant in the Lisbon study. Dr. Michael Martin, study director, observes the procedure
The University of Washington Department of Dental Public Health Sciences has had affiliation and exchange agreements with the University of Lisbon schools of Dentistry and Dental Hygiene, and through these agreements we had previously collaborated on projects for children from a large school system in Lisbon. The Casa Pia de Lisboa school system was established in the late 1700s, and today provides educational and cultural opportunities to approximately 4,100 children who are orphaned, from troubled homes, or otherwise disadvantaged. Many of these children are economically disadvantaged and have had no access to dental care. The school population is relatively homogeneous culturally and stable geographically. In a pilot feasibility study for the current project we were able to track virtually 100% of the children over five years. We plan to enroll about 500 children between 8 and 10 years of age in the Casa Pia system, all will receive comprehensive oral health care whether or not they qualify for participation in the study. Children will be initially screened for blood lead concentrations, urinary mercury, and the presence of existing amalgam fillings. Additionally the children will have a battery of neurobehavioral studies, nerve conduction velocity tests, and kidney function assays. Any with sigrificant abnormalities will be excluded from the study but not from receiving dental care for the duration of the project. We anticipate that we will ultimately enroll and have long-term observation of about 400 children. They will be reexamined yearly for all of the measurements, and safety of the trial will be monitored annually for at least five years.
UW faculty are responsible for the study design and implementation and for the management of the randomization scheme and biostatistical procedures. UW laboratories will analyze the blood and urine samples. UW faculty also are training Portuguese psychometrists to administer the specific neuro-behavioral tests. The University of Lisbon is recruiting Portuguese dentists, hygienists, and dental assistants to provide all treatment, and their study team will manage all day-to-day activities of arranging, testing, transportation, and treatment.
The determination of the safety of mercury amalgam is a public health question of potentially profound impact. The Casa Pia Study of the Health Effects of Dental Amalgams in Children will be an important step in providing objective answers.
Recommended Reading
Agency for Toxic Substances and Disease Registry: Toxicological Profile for Mercury (update), TP-93/10. Washington, DO Public Health Service, U.S. Department of Health and Human Services, 1994.
Echeverria D, Heyer N, Martin MD, et al: Behavioral effects of low-level exposure to HgO among dentists. Neurotoxicity and Teratology 1995; 17:161-168
Langan DC, Fan PL, Hoos AA: The use of mercury in dentistry: A critical review of the recent literature. JADA 1987; 115:867-880.
Martin MD, Naleway C, Chou HN: Factors contributing to mercury exposure in dentists. JADA 1995 126:1502-1511.
Authors
Michael D. Martin, D.M.D., M.S.D., M.P.H., M.A., Ph.D., directs the mercury amalgam study. He is an assistant professor of oral medicine and holds an adjunct appointment in dental public health sciences at the UW School of Dentistry.
Timothy A. DeRouen, Ph.D., is primary investigator of the mercury amalgam study He is chair of the Department of Dental Public Health Sciences at the UW School of Dentistry and professor of biostatistics at the UW School of Public Health and Community Medicine.
Brian G. Leroux, Ph.D., is an assistant professor of dental public health sciences and biostatistics at the University of Washington. He is the lead biostatistician for the project.
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Created: 5/6/98 Updated: 7/15/99
