Some of the most common dental restorative materials currently in use are dental amalgams, but these compounds contain approximately 50% mercury making their use controversial, particularly with young children who may be harmed by long-term exposure. Although there are some viable composite resin alternatives available, dental amalgams with mercury remain the treatment of choice for many practitioners. To determine the current risks and potential alternatives to dental amalgams, this paper provides a review of the relevant peer-reviewed and scholarly literature concerning these issues, followed by a summary of the research and important findings in the conclusion.
Review and Discussion
Dental amalgams are a commonly used dental restorative material, but amalgams contain a number of compounds including mercury (Hg) (Geier, Carmody, Kern & King, 2011). A report from Bradbard (1999) notes that despite the mercury content, dental amalgam has a long track record of use. In this regard, Bradbard advises that, "Amalgam restorations, better known as 'silver fillings' -- are the most widely used material to fill cavities in decayed teeth, technically known as caries. It has been used for 150 years; only gold has been used longer" (p. 22). Although a main component of dental amalgam is mercury, the compound contains a number of other metals and alloys as well. For instance, Bradbard reports, "Amalgam is composed of approximately equal parts of liquid mercury and alloy powder containing silver, tin, copper, and sometimes lesser amounts of zinc, palladium or indium" (p. 23).
Notwithstanding its lengthy track record, dental amalgam is increasingly viewed with concern by researchers and clinicians alike. According to Bradbard, "Despite amalgam's long history of use, some scientists and consumers are concerned that the mercury from amalgam restorations might be harmful. Nearly half of 1,000 adult Americans surveyed by the American Dental Association said they believed amalgam could cause health problems" (p. 23). In fact, a more recent American Dental Association survey determined that posterior composite resin restorations are currently more popular than amalgam restorations, at least in the United States; however, dental schools in different countries differ significantly concerning the methods they teach for use of composite resins (Ben-Gal & Weiss, 2011). The point is also made by Voynick (2004) that other countries are reevaluating the efficacy and safety of mercury-based amalgams for dental applications. According to Voynick, "Austria, Denmark, Germany, and Sweden are already phasing out the use of dental amalgam, and in the United States and Canada, many dentists have voluntarily discontinued its use" (p. 144). In fact, the European Union has taken steps to completely ban all mercury-based dental amalgams. In this regard, a report presented to the European Parliament cites the known dangers that are associated with even minute amounts of mercury exposure to pregnant women and young children. According to a report from the editors of European Social Policy, "EU health and environment experts are demanding that all use of mercury, particularly in medical devices, be banned. Mercury has long been recognized as a major source of toxicity in children causing reduced cognitive functioning, including reduced IQ" (Public health: Experts call for a total ban on mercury, 2007, p. 79).
Despite these trends in other countries, the American Dental Association has essentially circled its wagons in support of mercury-based amalgams. The position statement from the ADA indicates that besides "rare instances of local side effects of allergenic reactions, the small amount of mercury released from amalgam restorations, especially during replacement and removal, has not been shown to cause any . . . adverse health effects" (quoted in Voynick, 2004, p. 144). In addition, the position statement from the ADA also states that the organization "finds no justification for discontinuing the use of dental amalgam," a perspective that is mirrored by the U.S. Public Health Service (Voynick, 2004, p. 144).
The concern over dental amalgam is certainly not new, though. According to Robicsek (2002), "The mercury issue goes back at least to 1850, and no one has conclusively shown that mercury fillings are safe" (p. 8). This lack of certainty became even more pronounced during the late 20th century as clinicians gained additional experiences with these materials. In this regard, Robicsek (2002) emphasizes that:
There is voluminous information on this topic, starting with the well-known dentist Mark A. Breiner, who wrote Whole Body Dentistry. 'I had learned in dental school that amalgams ... were perfectly safe and posed no threat whatsoever to human health,' he writes. 'In 1978, my dental assistant's five-year-old daughter had her first cavity. I placed her first mercury amalgam filling. Two days later she had a seizure. Having faith in the ADA, I was stunned to find an abundance of documented research and scientific data that called into question the safety of amalgam use.' (p. 8)
In response to these growing concerns over the integrity and safety of the amalgam alloys in use and to provide reasonable assurance of the safety and effectiveness of these materials, the U.S. Food and Drug Administration (FDA) issued a final rule in 2006 that classified dental amalgam into class II; in addition, the final rule reclassified dental mercury from class I to class II, and designating a special control to support the class II classifications of these two devices together with the current class II classification of amalgam alloy (Dental devices, 2006). At present, all three of these dental devices are classified in a single regulation (Dental devices, 2006). A guidance document published by the U.S. Food and Drug Administration entitled, "Class II Special Controls Guidance Document: Dental Amalgam, Mercury, and Amalgam Alloy" currently serves as the special control instructions for these devices (Dental devices, 2006). At present, total replacement is the most common method used for defective amalgam restorations and this procedure represents a major component of restorative dental treatment, with the repair of these devices being an alternative for amalgam restorations that are characterized by localized defects (Popoff, Gonzales, Magalhaes, Moreira & Ferreira, 2011).
A continuing concern persists, though, that children's exposure to mercury vapor from dental amalgams can result in neurotoxicity (Bellinger & Daniel, 2007). According to these authorities, "Urinary mercury (U-Hg) excretion is a commonly used biomarker for mercury exposure from dental amalgam restorations"; however, they add that, "One single measure of amalgam exposure is insufficient" (Bellinger & Daniel, 2007, p. 441). These issues were also the focus of a study by Woods, Martin and Leroux (2007) who report, "Of particular public health concern has been possible neurologic impairment associated with prolonged exposure to elemental mercury vapor" (p. 1527). This concern is based on well established health hazards that can occur in young people who have been exposed to elementary mercury vapor for lengthy periods of time. In this regard, Woods et al. emphasize that, "Children are known to be particularly vulnerable to elemental mercury vapor, prolonged exposure to which may cause impairment of the developing central nervous system, along with attendant personality, motor function, and behavioral disorders" (p. 1527).
Other researchers cite the need for longitudinal studies to determine the cumulative effects of mercury from amalgam exposure for children because these types of studies will likely provide better reliability, precision and validity to the extent that time-sensitive amalgam exposure measures are employed (Maserejian & Trachtenberg, 2008). Despite the need for long-term studies to determine the cumulative effects of mercury from amalgam, straightforward counts of existing amalgam fillings are sufficient to identify amalgam-related current U-Hg levels (Maserejian & Trachtenberg, 2008).
The findings that have emerged from these studies must be considered in view of the fact that Hg exposure amounts are related to the size as well as the number of teeth that contain dental amalgams. Generally, the results observed in the seminal Casa Pia Children's Dental Amalgam Trial were congruent with the results of the study by Geier et al. (2011) who also identified a statistically significant dose-dependent correlation between cumulative exposure to Hg from dental amalgams and urinary Hg levels, after covariate adjustments were made. The results of the follow-up study by Geier et al. also showed that urinary Hg levels increased by 18% to 52% among 8 to 18-year-old individuals, respectively, with an average exposure to amalgams, in comparison to study subjects that did not have any amalgam exposure at all. In sum, the Geier et al. conclude that, "The results of our study suggest that dental amalgams contribute to ongoing Hg exposure in a dose-dependent fashion" (2011, p. 11).
The findings from the Geier et al. (2011) student were consistent with the result of the study by Woods et al. who conducted a 7-year longitudinal study concerning the effect of elemental mercury vapor on children's health. According to Woods et al. (2007), "A strong, positive correlation between mercury exposure from dental amalgam fillings and urinary mercury excretion over a 7-year longitudinal course of amalgam treatment in children" (p. 1530). Of particular note was an unexpected findings made by Woods and his associates in the course of this investigation. In this regard, Woods et al. add that, "However, significant differences…