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James S. Woods,¹ Michael D. Martin,² Brian G. Leroux,³ Timothy A. DeRouen,³ Jorge G. Leitão,⁴ Mario F. Bernardo,⁴ Henrique S. Luis,⁴ P. Lynne Simmonds,¹ John V. Kushleika,¹ and Ying Huang³

¹Department of Environmental and Occupational Health Sciences, ²Department of Oral Medicine, and ³Department of Dental Public Health Sciences, University of Washington, Seattle, Washington, USA; ⁴Faculdade de Medicina Dentaria, Universidade de Lisboa, Lisbon, Portugal

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 (~ 1.5 µg/L) . Mean urinary mercury concentrations in the amalgam group increased to a peak of ~ 3.2 µg/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.

Key words: amalgam, children, dental, mercury, urine. Environ Health Perspect 115:1527–1531 (2007) . doi:10.1289/ehp.10249 available via http://dx.doi.org/ [Online 28 June 2007]

Address correspondence to J.S. Woods, Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, WA 98105 USA. Telephone: (206) 685-3443. Fax: (206) 685-4696. E-mail: jwoods@u.washington.edu

The research was funded by Cooperative Agreement U01DE11894 from the National Institute of Dental and Craniofacial Research (NIDCR) of the National Institutes of Health.

J.G.L. is principal investigator for a clinical research project at the Biomaterials Laboratory at the University of Lisbon, which is supported by the Ivoclar Vivadent Company to test a novel indirect veneer material. Ivoclar Vivadent manufactures both composite resins and dental amalgams, but no product used in the process is discussed in this article, and J.G.L. has received no direct compensation from this contract. M.F.B. has received finanacial supoort from Dentsply DeTry Company, which manufactures dental instruments and amalgam, to travel to the University of Washington for professional development in research methods. None of the other authors declares competing financial interests.

Received 9 March 2007 ; accepted 28 June 2007.