The association of dental caries with blood lead in children when adjusted for IQ and neurobehavioral performance

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Abstract

Associations between childhood lead exposures and dental caries in children have been reported for over 30 years, with widely varying findings and conclusions, and using measures of lead exposure which ranged from food sources and water to tooth, hair or blood lead concentrations.

Objectives

This study examined the relationship of lead exposure and dental caries in a population of normatively healthy children.

Methods

This cross-sectional study used a population of 507 children aged 8–12 who were participating in a clinical trial of dental materials to examine the relationship between lead and caries. Blood lead concentrations and dental caries were examined for association in both primary and permanent teeth. Because it is possible that neurobehavioral status could be associated with both lead exposure and dental caries prevalence, we also examined neurobehavioral status of the subjects.

Results

A gender-specific association (males only) between lead exposure and dental caries was found in primary teeth only. Neurobehavioral measures and IQ were not associated with caries status in this population.

Conclusions

This study did not support neurobehavioral status as mediating any association between lead exposure and caries in a normatively healthy population. A gender-specific association between lead and caries not previously reported was found in primary teeth, and no biological explanation for this has been suggested. We conclude that this study provides only weak evidence, if any, for an association of low-level lead exposure with dental caries.

Introduction

Positive associations between childhood lead exposures and dental caries in children have been reported for over 30 years, although with widely varying findings and conclusions and using measures of lead exposure which ranged from food sources and water to tooth, hair or blood lead concentrations. Barmes (1969) reported finding an association between dietary lead and dental caries in villagers in New Guinea. Ludwig et al. (1970) reported an association between the concentration of lead in drinking water and caries in children examined in 19 towns in the Eastern United States, and Brudevold et al. (1977) using enamel biopsies from children aged 9–12 in Cambridge, Massachusetts, found higher decayed and filled teeth (DFT) scores and decayed and filled surface (DFS) scores in permanent teeth only in a dichotomized “high (vs. low) lead” group. Gil et al. (1996) reported positive associations between enamel lead concentrations and dental caries in a cross-sectional study of 220 subjects of mixed ages from 10 to > 60 years.

Moss et al. (1999) reporting on the largest population studied to date using data from the NHANES III, found significant associations between blood lead concentration and dental caries in both primary and permanent teeth for children in age groups 2–5 and 6–11, after adjusting for potential confounders such as diet and dental care. In children 5–17 years of age, an increase of 5 μg/dL of blood lead was associated with a near doubling of caries in this study. Campbell et al. (2000), using a retrospective cohort design with 248 school-age subjects with blood lead levels measured between 18–37 months of age, and dichotomized to < 10 μg/dL, or ≥ 10 μg/dL found only a marginal association of blood lead concentration with dental caries, and only in deciduous teeth. Gemmel et al. (2002) in a cross-sectional study of 498 children aged 6–10 in the New England region of the United States found an association of blood lead concentration with caries in deciduous teeth, but only in children in the “urban” (vs. rural) subgroup of subjects. Youravong et al. (2006) examined children aged 6–11 living in a lead contaminated area of Thailand, and reported that increased blood lead was associated with caries in primary teeth, but not in permanent teeth.

These studies clearly are not in unequivocal agreement. Most authors have concluded that although there may be a potential relationship between childhood lead exposure and dental caries, the association is weak, and that the exposure to lead itself only partially explains the increase in caries. Mechanisms which have been offered to explain the potential association include lead effects on salivary gland development and function (Watson et al., 1997, Bowen, 2001), effects on enamel formation (Lawson et al., 1971, Kato et al., 1977, Appleton, 1991, Watson et al., 1997), and an interference with fluoride uptake in saliva (Gerlach et al., 2002). Each of these potential mechanisms remains unproven, and there are published studies for each which both support and do not support the mechanisms.

Lead exposure is well known to produce detrimental effects on neurobehavioral function. Because neurobehavioral deficits may also be associated with an increase in dental caries due to an interaction with oral hygiene behaviors, it is possible that the effect of lead on caries may be actually an indirect one, mediated by neurobehavioral deficits. Associations between neurobehavioral measures including IQ, and dental caries have been reported only in populations with significant neurobehavioral deficits such as mental retardation, multiple sclerosis, or dementia (Steinberg and Zimmerman, 1967, Shanker et al., 1983, Forsberg et al., 1985, McGrother et al., 1999, Henriksen et al., 2005). Investigations of these associations have not been described in a population of normatively healthy children. In the present study we therefore examined the associations in a normatively healthy study population between 1. lead exposure and neurobehavioral measures, 2. caries and neurobehavioral measures, and 3. lead exposure and caries.

Section snippets

Study population

Developmentally normal children who were taking part in a randomized clinical trial to examine the potential health effects of dental amalgam in children (DeRouen et al., 2002, DeRouen et al., 2006), served as the study population. In brief, this trial was a randomized, prospective clinical safety trial of mercury-containing dental amalgam as a filling material. 507 children from 7 schools in the Casa Pia school system in Lisbon, Portugal were enrolled in the trial. Inclusion criteria were: age

Results

Table 1 provides descriptive characteristics of the study sample population. Children were enrolled into the study from 7 schools in the Casa Pia school system. There were no significant differences between schools of origin for age, gender, race, IQ, caries or blood lead.

In examining the relationship between gender and the neurobehavioral measures alone, there was no gender difference in IQ. However, males scored lower in the attention domain (p < 0.001), and females scored lower in the

Discussion

In examining the relationship of blood lead to neurobehavioral measures in this study population, we found that only two of the four measures utilized were associated with blood lead (Attention and Visuomotor domains) and that these were differentially associated in males and females, i.e. increased lead was associated with decreased Attention domain scores in males only, and with decreased Visuomotor domain scores in females only. IQ, a global assessment score, was not associated with blood

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