Renal effects of dental amalgam in children: The New England children's amalgam trial

BACKGROUND: Mercury is nephrotoxic and dental amalgam is a source of mercury exposure. METHODS: Children 6-10 years of age (n = 534) with two or more posterior teeth with caries but no prior amalgam restorations, were randomized to one of two treatments-amalgam or resin composite (white fillings)-used for caries treatment during 5 years of follow-up. The primary outcome was change in IQ, but important secondary outcomes were effects on markers of glomerular and tubular kidney function: urinary excretion of albumin, alpha-1-microglobulin (AlM), gamma-glutamyl transpeptidase (gamma-GT), and N-acetyl-beta-D-glucosaminidase (NAG). These markers were measured on several occasions during the trial, together with urinary mercury and covariates. We evaluated the results using repeated-measures analyses. RESULTS: There were no significant differences between treatment groups in average levels of renal biomarkers, nor significant effects of number of dental amalgams on these markers. There was, however, a significantly increased prevalence of microalbuminuria (MA) among children in the amalgam group in years 3-5 (adjusted odds ratio 1.8; 95% confidence interval, 1.1-2.9). Most of these cases are likely to be temporary MA, but 10 children in the amalgam group had MA in both years 3 and 5, versus 2 children in the composite group (p = 0.04). There were no differences in the occurrence of high levels of renal tubular markers (AlM, gamma-GT, or NAG). CONCLUSIONS: The increase in MA may be a random finding, but should be tested further. The results did not support recent findings in an observational study of an effect of low-level mercury on tubular biomarkers in children.