Neuropsychological and Renal Effects of Dental Amalgam in Children: A Randomized Clinical Trial

Howard E. Strassler, DMD

Bellinger DC, Trachtenberg F, Barregard L, et al. JAMA. 2006;295(15): 1775-1783.

Abstract

CONTEXT: No randomized trials have been published that address the concern that inhalation of mercury vapor released by amalgam dental restorations causes adverse health effects. OBJECTIVE: To compare the neuropsychological and renal function of children whose dental caries were restored using amalgam or mercury-free materials. DESIGN AND SETTING: The New England Children’s Amalgam Trial was a 2-group randomized safety trial involving 5 community health dental clinics in Boston, Mass, and 1 in Farmington, Me, between September 1997 and March 2005. PARTICIPANTS AND INTERVENTION: A total of 534 children aged 6 to 10 years at baseline with no prior amalgam restorations and 2 or more posterior teeth with caries were randomly assigned to receive dental restoration of baseline and incident caries during a 5-year follow-up period using either amalgam (n = 267) or resin composite (n = 267) materials. MAIN OUTCOME MEASURES: The primary neuropsychological outcome was 5-year change in full-scale IQ scores. Secondary outcomes included tests of memory and visuomotor ability. Renal glomerular function was measured by creatinine-adjusted albumin in urine. RESULTS: Children had a mean of 15 tooth surfaces (median, 14) restored during the 5-year period (range, 0–55). Assignment to the amalgam group was associated with a significantly higher mean urinary mercury level (0.9 vs 0.6 µg/g of creatinine at year 5, P < .001). After adjusting for randomization stratum and other covariates, no statistically significant differences were found between children in the amalgam and composite groups in 5-year change in full-scale IQ score (3.1 vs 2.1, P = .21). The difference in treatment group change scores was 1.0 (95% confidence interval, -0.6 to 2.5) full-scale IQ score point. No statistically significant differences were found for 4-year change in the general memory index (8.1 vs 7.2, P = .34), 4-year change in visuomotor composite (3.8 vs 3.7, P = .93), or year 5 urinary albumin (median, 7.5 vs 7.4 mg/g of creatinine, P = .61). CONCLUSIONS: In this study, there were no statistically significant differences in adverse neuropsychological or renal effects observed over the 5-year period in children whose caries were restored using dental amalgam or composite materials. Although it is possible that very small IQ effects cannot be ruled out, these findings suggest that the health effects of amalgam restorations in children need not be the basis of treatment decisions when choosing restorative dental materials.

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