Dental amalgam has been used in the routine dental care of hundreds of millions of Americans, both children and adults, for the past 150 years. Amalgam is the most widely used dental restorative material because it can be applied in a broad range of clinical situations and is durable, easy to use, relatively insensitive to variations in handling technique and oral conditions, and inexpensive compared to alternative materials. More than 200 million restorative procedures were performed by U.S. dentists in 1990, of which amalgam restorations accounted for approximately 96 million (Nash, 1991).

Dental amalgam has a much longer service record than most drugs and biomaterials in use today and, except for gold, all other dental restorative materials. There is more information about dental amalgam than about any other dental restorative material presently used. Yet, concerns are raised periodically about the safety of dental amalgam relative to one of its ingredients—elemental mercury.

These concerns have stimulated a comprehensive scientific assessment by the U.S. Public Health Service (PHS) of the benefits and risks of amalgam. To conduct this assessment, the Assistant Secretary for Health (ASH) charged the PHS Committee to Coordinate Environmental Health and Related Programs (CCEHRP) to examine the potential health risks of dental amalgam. This task was assumed by the standing Risk Assessment Subcommittee of CCEHRP. In order to facilitate a complete review of amalgam, an ad hoc subcommittee of CCEHRP was established in March 1991 to examine the benefits of amalgam. The reports of these two committees will be reviewed by the Risk Management Subcommittee of CCEHRP, which will develop an overall PHS statement on the risks and benefits of dental amalgam.

The present report was prepared by the Ad Hoc Subcommittee on the Benefits of Dental Amalgam. This subcommittee assessed the benefits of dental amalgam to oral and general health. In so doing, the subcommittee also compared dental amalgam to dental restorative materials that are or potentially may be available for achieving similar health and functional benefits.

Dental amalgam is a mixture of approximately equal parts of elemental liquid mercury (43 to 54 percent) and an alloy powder containing a mixture of other metals, predominantly silver, but also tin and copper, with smaller amounts of zinc, palladium, or indium sometimes present. The relative proportion of these ingredients may vary, but the ingredients themselves have remained essentially the same through the years.

Mercury is distributed widely in the environment; it is found in food, air, and prescribed drugs and medicines. Mercury from dental amalgam restorations has generally been reported to contribute a relatively small percentage of an individual's total daily mercury exposure (Vostal, 1972; Shibko et al, 1976; WiIIiams, 1981; Olsson and Bergman, 1987; Mackert, 1987; Snapp, et al., 1989). Some studies, however, suggest that the relative contribution is higher (Clarkson et al., 1988; World Health Organization, 1991). The health effects from exposure to different levels of elemental mercury have been documented for decades, with much of the information derived from case reviews of exposure among industrial workers. The mercury in dental amalgam was considered to be inert until the development of highly sensitive devices for measuring mercury vapor, which permitted the discovery of previously undetectable levels of mercury vapor from dental restorations (Gay et al., 1979).

Whether such levels pose a risk to health is difficult to determine. Nevertheless, key questions must be raised. What are the risks of dental amalgam? What are the benefits of dental amalgam? Are these benefits and risks comparable to those of other dental restorative materials? Should we continue to use dental amalgam? If not, what are the implications of replacing dental amalgam with other restorative materials?

The Federal Government has sought over the years to explore concerns and to review existing data on dental amalgams. The present effort is the first formal attempt by PHS to specifically focus on the benefits of dental amalgam use.

During the 1980's, the National Institute of Dental Research (NIDR) sponsored a number of workshops, conferences, and meetings addressing the safety of dental restorative materials and indications for their use. Recommendations from individual meetings often have led to subsequent consultations and deliberations. For example, as a result of an NIDR consultant meeting in 1983 that focused on mercury toxicity, the NIDR supported additional meetings on the biocompatibility of metals (1984); biocompatibility, toxicity, and hypersensitivity in dentistry and dental amalgam and mercury toxicity (1985); the criteria for placement and replacement of dental restorations (1987); and the possible systemic responses from dental amalgam (1991). All of these meetings involved experts and recognized authorities from around the world.

Continuing to address the safety of all dental restorative materials, the NIDR, in collaboration with the Office of Medical Applications of Research, National Institutes of Health (NIH), convened in August 1991 a workshop on the effects and side effects of dental restorative materials. Other recent meetings have been held by the National Institute of Environmental Health Sciences and the Food and Drug Administration (FDA).

In addition, the American Dental Association (ADA) has conducted numerous professional symposia and has published scientific articles relating to dental amalgam and other restorative materials. Collectively, these deliberations have resulted in continued support for the routine use of dental amalgam as a restorative material, as evidenced by recent statements from a number of professional and voluntary associations (Consumer Union, 1990; ADA, 1991; National Multiple Sclerosis Society, 1991).

Since the inception of the U.S. Medical Device Amendments of 1976, the FDA has regulated the components of dental amalgam. An FDA amalgam task force was formed in 1984 to monitor the scientific literature and provider- and patient-supplied information related to amalgam use.

A recent meeting of the FDA Dental Products Panel on March 15, 1991, brought together world experts in mercury toxicity, medical and dental experts, and others in order to address issues related to amalgam safety and toxicity. While reaffirming the safety of amalgam for current use as a restorative material, the FDA panel called for additional research to answer some of the important questions that have been raised in animal studies. The FDA also participated in the present CCEHRP subcommittees to assess the risks and benefits of dental amalgam and will take the lead in determining appropriate future regulatory actions.

The oral health of the American public and the practice of dentistry have undergone dramatic changes in the past 200 years. During the 18th and early 19th centuries, the public was resigned to the ravages of dental caries and, ultimately, the loss of many—and often all—teeth. Toothaches were treated commonly by extraction. By the middle of the 19th century, the development of restorative dentistry enabled individuals to retain teeth that became carious. The subsequent discovery of nitrous oxide and local anesthetics, along with improved methods of cutting tooth structure, further enhanced dental treatment. Extractions were still common, but replacement of portions of teeth, or even entire teeth, through more modern flexed and removable partial dentures became possible.

In the 20th century, restorative and prosthetic dentistry became more sophisticated, facilitated by the continuing development of clinical equipment, techniques and materials, including the high-speed drill. Over the past several decades, attention has been focused on preventing dental caries. The use of topical and systemic fluorides, improved oral hygiene products and practices, dietary modifications and dental sealants has contributed to dramatic declines in dental caries among school-aged children. In fact, smooth-surface caries (in contrast to pit and fissure caries) have been reduced to negligible levels in most children (NIDR, 1989). There also is some evidence of a decline in dental caries among young adults (Brown and Swango,1991) and clear evidence of a decline in tooth loss for Americans of all ages (Ismail et al., 1987; Meskin and Brown, 1988; Brown and Swango, 1991).

Further, among those who continue to experience caries, there are consistent clinical reports that, compared to prior years, lesions are smaller, easier to treat, and require less destruction of healthy tooth structure in order to restore form and function. These trends suggest that the number, size, and frequency of replacement of restorations and, thus, overall exposure to dental restorative materials will decrease.

Preliminary evidence for this trend comes from a recent survey indicating that a significant decline in the use of dental amalgam has taken place since 1979 (Nash, 1991). This comes at a time when newer materials, such as posterior composites, pit and fissure sealants, preventive resin restorations, and glass ionomer cements, are being integrated into dental practice. Some of these materials have improved adhesive characteristics, so that removal of tooth structure can be minimized. Others, such as high copper amalgam alloys, which have been in widespread use for some years, demonstrate improved physical properties. Some of these new alloys also contain less mercury than the dental amalgam used several decades ago. If caries rates continue to decline and new biocompatible materials are proven to be effective, then fewer restorations will be needed and materials other than dental amalgam will be used relatively more frequently.

Nevertheless, it must be recognized that serious dental caries problems remain in the population. Analysis of epidemiological data suggests that the dental caries that occur among children today are concentrated in certain segments of the population. For those populations at high risk (PHS, 1990), the rate and severity of caries reflect patterns documented among the general population a generation ago.

As the population ages and adults retain more teeth, root caries are likely to become an increasing concern, along with coronal caries in adults whose general health is compromised or who suffer the side effects of medication or therapy, such as radiation treatment for head and neck cancer.

Finally, one must remember that there are so many restorations already in the mouths of patients that decades of replacement work lie ahead. Few restorations can be expected to last the lifetime of an individual. As the lifespan of individual Americans continues to increase, so will the need for replacement restorations. Even today, up to two-thirds of the restorations currently provided are estimated to be replacements (Maryniuk and Kaplan, 1986), contributing significantly to the more than $30 billion that is spent for dental care each year in the United States (Nash, 1991).

In developing this report, the Ad Hoc Subcommittee on the Benefits of Dental Amalgam acknowledged the changing environment of dental practice and oral health. This environment makes any study of the benefits of dental amalgam and other restorative materials complex. Inherent in the assessment of benefits is an assessment of the risks incurred. In addition, a relative comparison of dental amalgam to other available materials is warranted, which necessitates a discussion of the potential risks of other materials that might be used.

The subcommittee sought to address the following key questions:

• What are the basic benefits of dental amalgam?
• What are the benefits relative to other available, appropriate materials?

The subcommittee addressed potential benefits to the patient, the public and the provider.

Several approaches for accessing information on the benefits of dental amalgam were used. A literature search was performed using the Medline system to identify articles published from 1980 through July 1991. Experts in the field of dental materials were asked to identify text materials that might be relevant. Several review papers were commissioned and prepared by expert consultants. These papers included useful bibliographies and provided validation for the overall scope and direction of the report. The papers and report of the NIH/NIDR technology assessment conference on the effects and side effects of dental restorative materials, held in August 1991, also were reviewed to assure that the scientific assessment of benefits and of the biocompatibility of dental restorative materials was as current as possible.

The scientific material reviewed for this report includes well-quantified, prospective studies using objective assessment methods; cross-sectional studies reporting data for a given point, or points, in time; retrospective studies reporting the longevity of restorations; laboratory reports; and articles published in rigorously reviewed scientific journals. The subcommittee's conclusions and recommendations reflect an overall assessment of the relevant science on the use and benefits of dental amalgam and other dental restorative materials.

The chapters that follow focus on comparisons between the characteristics of available and emerging restorative materials used in the restoration of posterior teeth and those of dental amalgam; the biocompatibility of dental restorative materials which are potential alternatives to amalgam; the relative costs and benefits of dental amalgam and other restorative materials; and policy and research implications regarding dental amalgam and alternative dental restorative materials. An extensive list of references also is provided.