Neurobehavioral Effects of Dental Amalgam in Children: A Randomized Clinical Trial

Howard E. Strassler, DMD

DeRouen TA, Martin MD, Leroux BG, et al. JAMA. 2006;295(15):1784-1792.

Abstract

CONTEXT: Dental (silver) amalgam is a widely used restorative material containing 50% elemental mercury that emits small amounts of mercury vapor. No randomized clinical trials have determined whether there are significant health risks associated with this low-level mercury exposure. OBJECTIVE: To assess the safety of dental amalgam restorations in children. DESIGN: A randomized clinical trial in which children requiring dental restorative treatment were randomized to either amalgam for posterior restorations or resin composite instead of amalgam. Enrollment commenced February 1997, with annual follow-up for 7 years concluding in July 2005. SETTING AND PARTICIPANTS: A total of 507 children in Lisbon, Portugal, aged 8 to 10 years with at least 1 carious lesion on a permanent tooth, no previous exposure to amalgam, urinary mercury level < 10 µg/L, blood lead level < 15 µg/dL, Comprehensive Test of Nonverbal Intelligence IQ > 67, and with no interfering health conditions. INTERVENTION: Routine, standard-of-care dental treatment, with one group receiving amalgam restorations for posterior lesions (n = 253) and the other group receiving resin composite restorations instead of amalgam (n = 254). MAIN OUTCOME MEASURES: Neurobehavioral assessments of memory, attention/concentration, and motor/visuomotor domains, as well as nerve conduction velocities. RESULTS: During the 7-year trial period, children had a mean of 18.7 tooth surfaces (median, 16) restored in the amalgam group and 21.3 (median, 18) restored in the composite group. Baseline mean creatinine-adjusted urinary mercury levels were 1.8 µg/g in the amalgam group and 1.9 µg/g in the composite group, but during follow-up were 1.0 to 1.5 µg/g higher in the amalgam group than in the composite group (P < .001). There were no statistically significant differences in measures of memory, attention, visuomotor function, or nerve conduction velocities (average z scores were very similar, near zero) for the amalgam and composite groups over all 7 years of follow-up, with no statistically significant differences observed at any time point (P values from .29 to .91). Starting at 5 years after initial treatment, the need for additional restorative treatment was approximately 50% higher in the composite group. CONCLUSIONS: In this study, children who received dental restorative treatment with amalgam did not, on average, have statistically significant differences in neurobehavioral assessments or in nerve conduction velocity when compared with children who received resin composite materials without amalgam. These findings, combined with the trend of higher treatment need later among those receiving composite, suggest that amalgam should remain a viable dental restorative option for children.

COMMENTARY

In the same issue of JAMA as these two papers, there was also a commentary on the topic of amalgam safety. Both studies reached similar conclusions that the children who received dental restorative treatment with amalgam did not, on average, have statistically significant differences in neurobehavioral assessments or in nerve conduction velocity when compared to children who received composite materials without amalgam. Both studies concluded that amalgam should remain a viable restorative treatment option for children. They also make note that these studies drew their conclusions over the course of evaluation—one study over 7 years and the other study over 5 years. In either instance, both studies state that a follow-up might be needed to appreciate any other subtle toxic effects that might be associated with dental amalgam.   Before one either agrees or disagrees with these two benchmark studies with reasons relating to excellent research design or poor research design or even a conspiracy theory, it should be noted that one of these clinical research studies was funded by a cooperative agreement from the National Institute of Dental and Craniofacial Research (NIDCR) and the other study was funded by the NIDCR and the New England Research Institutes. These two multicenter studies were very well designed and extremely comprehensive, well beyond what other studies have done in evaluating dental silver amalgam safety and its effects. These studies will probably not change a clinician’s practice habits or philosophy of practice—you may or may not continue to use amalgam. What is of interest is that in recent years, dental composites and sealants have come under attack for medical safety. Neither of these studies evaluated the safety of composite used by itself. What should be important for your practice decisions is that for these studies, children in the composite group exhibited a higher treatment need at 5 or more years after the initial treatment when compared to the amalgam group. This parallels other published research. Why a higher treatment need? These composite resins were adhesively bonded following the existing standards of care in the United States and Portugal. There is no doubt that the placement of composite resin requires a greater attention to detail and a more controlled operative field. Recently, there have been questions raised about the ability of light to cure composite resin to the gingival margins of Class 2 restorations in the shorter time increment recommended by manufacturers; the position and angulation of the light guide when curing posterior composite resins; and a difference in adhesion between in vitro and in vivo data to both enamel and dentin. The durability of dentin bonding has also come into question. When placing posterior composite resins, use your best practice standards and reevaluate your restorations over time to continue to improve your standard of care. The issue of amalgam and composite resin will not go away—we need to be diligent and continue to evaluate these issues.

About the Author

Howard E. Strassler, DMD Professor and Director of Operative Dentistry, Department of Endodontics, Prosthodontics and Operative Dentistry University of Maryland Dental School, Baltimore, Maryland