The contribution of dental amalgam to urinary mercury excretion in children

Abstract

Background: Urinary mercury concentrations are widely used as a measure of mercury exposure from dental amalgam fillings. No studies have evaluated the relationship of these measures in a longitudinal context in children.

Objective: We evaluated urinary mercury in children 8-18 years of age in relation to number of amalgam surfaces and time since placement over a 7-year course of amalgam treatment.

Methods: Five hundred seven children, 8-10 years of age at baseline, participated in a clinical trial to evaluate the neurobehavioral effects of dental amalgam in children. Subjects were randomized to either dental amalgam or resin composite treatments. Urinary mercury and creatinine concentrations were measured at baseline and annually on all participants.

Results: Treatment groups were comparable in baseline urinary mercury concentration (approximately 1.5 microg/L). Mean urinary mercury concentrations in the amalgam group increased to a peak of approximately 3.2 microg/L at year 2 and then declined to baseline levels by year 7 of follow-up. There was a strong, positive association between urinary mercury and both number of amalgam surfaces and time since placement. Girls had significantly higher mean urinary mercury concentrations than boys throughout the course of amalgam treatment. There were no differences by race in urinary mercury concentration associated with amalgam exposure.

Conclusions: Urinary mercury concentrations are highly correlated with both number of amalgam fillings and time since placement in children. Girls excrete significantly higher concentrations of mercury in the urine than boys with comparable treatment, suggesting possible sex-related differences in mercury handling and susceptibility to mercury toxicity.

Keywords: amalgam; children; dental; mercury; urine.

Figure 1

Histograms of baseline urinary mercury concentrations in amalgam (A) and composite (B) treated groups. Heights of the bars represent the numbers of subjects with values within the indicated range. The distributions of baseline urinary mercury levels were similar in the two treatment groups.

Figure 2

Mean urinary mercury concentrations, unadjusted (A) and creatinine-adjusted (B), for the amalgam group and composite group. Error bars show 95% confidence intervals for the group means. Group differences were highly statistically significant (p < 0.001) for both measures at follow-up years 2 through 6. The group differences at year 7 were not significant for unadjusted mercury (p = 0.07) but significant for adjusted mercury (p = 0.007).

Figure 3

Mean urinary mercury concentrations for the amalgam group and composite group separately for male (A) and female (B) participants. Error bars show 95% confidence intervals for the group means. Differences between males and females in the amalgam group were statistically significant (p < 0.05) at all follow-up years except follow-up year 3. The sex comparisons were not altered significantly by adjustment for creatinine (results not shown).

Figure 4

The increase in urinary mercury concentration is influenced by both the amount and timing of amalgam treatment. Children in the amalgam group were categorized according to the number of amalgam surfaces placed at baseline—(A) 0–4; (B) 5–9; (C) > 9—and the number of additional amalgam surfaces placed in subsequent years. The values plotted are the differences between mean urinary mercury in a particular subgroup of amalgam-treated children compared with mean urinary mercury concentration in the composite group at each year.