title: Dental amalgam exposure and urinary mercury levels in children: the New England Children's Amalgam Trial.
abstract: BACKGROUND
  Urinary mercury (U-Hg) excretion is a commonly used biomarker for mercury exposure from dental amalgam restorations.
  
  
  OBJECTIVE
  Our goal was to determine the most efficient measure of dental amalgam exposure for use in analyses concerning U-Hg in children.
  
  
  METHODS
  We analyzed time-sensitive longitudinal amalgam exposure data in children randomized to amalgam restorations (n = 267) during the 5-year New England Children's Amalgam Trial. We calculated 8 measures of amalgam, evaluating current versus cumulative exposure, teeth versus surfaces, and total versus posterior occlusal amalgams. Urine samples collected during follow-up years 3-5 were analyzed for mercury excretion. Multivariate models for current and cumulative U-Hg excretion estimated associations between exposures and U-Hg.
  
  
  RESULTS
  At the end of follow-up, the average (+/- SD) cumulative exposure was 10.3 +/- 6.1 surfaces and 5.7 +/- 2.9 teeth ever filled with amalgam, corresponding to 30 +/- 21 surface-years. Amalgam measures and U-Hg were moderately correlated. Of amalgam exposure measures, the current total of amalgam surfaces was the most robust predictor of current U-Hg, whereas posterior occlusal surface-years was best for cumulative U-Hg. In multivariate models, each additional amalgam surface present was associated with a 9% increase in current U-Hg, and each additional posterior occlusal surface-year was associated with a 3% increase in cumulative U-Hg excretion (p < 0.001).
  
  
  CONCLUSIONS
  One single measure of amalgam exposure is insufficient. Studies of cumulative effects of mercury from amalgam exposure in children are likely to have improved validity and precision if time-sensitive amalgam exposure measures are used. In contrast, simple counts of current amalgam fillings are adequate to capture amalgam-related current U-Hg.
authors.affiliation: New England Research Institutes, 9 Galen Street, Watertown, MA 02472, USA. nmaserejian@neriscience.com
authors.forename: Nancy Nairi
authors.initials: NN
authors.lastname: Maserejian
authors.forename: Felicia L
authors.initials: FL
authors.lastname: Trachtenberg
authors.forename: Susan F
authors.initials: SF
authors.lastname: Assmann
authors.forename: Lars
authors.initials: L
authors.lastname: Barregard
mesh_terms: D002648:Child; D003723:Dental Amalgam; D005260:Female; D006801:Humans; D008297:Male; D008628:Mercury / Q000652:urine*
chemical_list: D003723:Dental Amalgam; D008628:Mercury