Are dental amalgams toxic to children? Comment on 2 recently published randomized controlled trials.

When I graduated from dental school in 1987, dental amalgam was essentially the only material available for the direct restoration of carious posterior teeth. Dentin bonding was in its first generation of technological development in restorative dentistry, and composite resin restoration of posterior teeth was carried out with caution by some dentists, but avoided by most. Even at that time, there was a long history of concern over the biocompatability of dental amalgam, which is 50% mercury by weight. Yet, in dental school, I was taught that amalgam was a safe restorative material and that composite resins were unsuitable for the occlusal surfaces of posterior teeth. I was never given a scientific explanation for these teachings. Soon after I graduated, I took it upon myself to search the literature to explore the controversy and determine the safety of amalgam in dental practice. In a review entitled “Mercury and dentistry, the controversy continues,”1 I summarized then-current evidence on the biocompatibility of dental amalgam. This evidence consisted of results from animal studies, anecdotal reports, cross-sectional studies, case-series reports and some poor-quality retrospective cohort reviews. I concluded that, although the levels of mercury in blood, urine and expired air were positively correlated with the number of amalgam restorations in the oral cavity, these levels were well below the threshold considered to be dangerous. Furthermore, considering its long success in clinical practice in managing the most prevalent disease (dental caries) in western society, there was no clinical or epidemiologic evidence to suggest that dental amalgam posed a public health risk. In 1990, CBS’s highly rated television news magazine 60 Minutes aired a story on the safety of dental amalgam.2 It implied that members of the dental profession were knowingly poisoning their patients with amalgam because most simply did not possess the clinical skills to use the newer, better and safer alternative materials. Such an inference only demonstrated the ignorance or bias of the news piece, considering the complex biomechanical cavity preparation required for amalgam restoration compared with that for a posterior composite resin restoration. In the mid-1990s, Health Canada commissioned Dr. Mark Richardson to review the biologic risk of dental amalgams. He presented his non-systematic review on August 18, 1995,3 concluding that, “There are insufficient published data on the potential health effects of dental amalgam specifically to support or refute the diverse variety of health effects attributed to it.” Nevertheless, Are Dental Amalgams Toxic to Children? Comment on 2 Recently Published Randomized Controlled Trials