This secondary analysis of a randomized trial of amalgam and composites found no evidence of associations between dental restoration material and changes in BMI, body fat percentage, or height velocity among children through 5 yrs of follow-up. Girls assigned to composites tended to have slightly greater increases in BMI and body fat percentage compared with girls assigned to amalgam, but the differences were not statistically significant. The finding that greater treatment level on primary teeth was associated with greater increases in body fat percentage over follow-up was observed for both treatment groups. Thus, overall, children who received composite or amalgam restoration materials experienced similar growth during the study period.
A limitation of this study is the lack of biomarker data on the children’s exposure to monomers used in dental composites. Numerous experimental studies have shown that the bisGMA-based composite resulted in bisGMA, TEGDMA, and BPA release (Pulgar et al., 2000
; Al-Hiyasat et al., 2004
; Ortengren et al., 2004
; Yap et al., 2004
; Sasaki et al., 2005
), and one small study found that children’s urinary BPA concentrations remained elevated 14 days post-treatment (Martin et al., 2005
). Chronic low-dose exposure to these resins over the life of the restoration is plausible, because chemical and mechanical interactions in the oral environment cause degradation over time, allowing unpolymerized monomers to leach out (Van Landuyt et al., 2011
). However, the quantity and duration of resins released in or absorbed by the human body after the placement of dental materials and during the entire life of the restoration in the mouth have not been adequately studied.
A strength of the current study is that repeated measures of growth and development, with detailed longitudinal data on dental treatments, were collected prospectively through 5 yrs of follow-up. Moreover, the randomized trial design ensured no self-selection in dental treatment materials, minimizing the possibility of confounding for intent-to-treat analyses. In analyses of received treatment levels, separating bisGMA- and UDMA-based composites, we had the unique advantage of conducting parallel analyses using the amalgam group primary/permanent teeth data. This comparison indicated that the observed associations between UDMA-based compomer and greater increases in body fat were attributable to confounding by factors related to severity of dental disease on primary teeth, rather than to dental treatment itself. Plausible factors underlying these associations include diet, such as consumption of sugar-sweetened beverages (Blum et al., 2005
; Ebbeling et al., 2006
). NECAT did not collect detailed dietary data. Nevertheless, in the primary analysis of randomized treatment group, the groups were balanced in dietary intakes of general food groups, such as fruits/vegetables and fish.
Our analysis of age of menarche was exploratory and had several limitations. The menarche analysis was restricted to a small number (n = 113) of girls from one geographic stratum (rural Maine). NECAT did not have a sufficiently long follow-up period to determine age of menarche for all female participants. Although the median age at menarche of 12.5 yrs in NECAT was similar to that reported in NHANES 2001 (Parent et al., 2003
), our calculation of age at menarche excluded 43% of the girls, because they were pre-menarcheal at the end of the study (their median age was 12.1 yrs at study’s end). Given the higher obesity prevalence in NECAT, it is interesting that menarche did not occur earlier in NECAT compared with the general population (Ogden et al., 2006
). In the survival analysis, girls assigned to composites had a lower risk of menarche during the follow-up period. However, there was no association between received treatment level of composites and menarche.
Mercury has also been implicated as an endocrine disruptor (Tan et al., 2009
). The only known published study of mercury exposure and menarche concurrently measured fasting blood mercury concentrations and self-reported menarche (yes/no) among 138 girls aged 10 to 16.9 yrs old in the Akwesasne Mohawk Nation (U.S. and Canadian border). Higher mercury concentrations were associated with higher odds of a girl’s having reached menarche, but the association was not significant after adjustment for age and socio-economic status (Denham et al., 2005
). Interactions among various environmental exposures, diet, and genetic susceptibility may together determine onset of puberty and age of menarche (Parent et al., 2003
). Thus, analysis of these exploratory NECAT data helps inform hypotheses for future testing in larger samples, rather than providing tenable conclusions. Additional studies of environmental contributors to menarche are necessary.
In summary, there were no associations between composite dental materials and physical development, including changes in BMI, body fat percentage, and height velocity, over 5 yrs of follow-up. Numerous genetic, dietary, environmental, and behavioral factors determine physical development and weight changes. In the context of these other predictors of physical development, the effects of resin-based dental materials, if any, may be difficult to discern. Nonetheless, there is compelling evidence that chemical monomers shown to have adverse effects in experimental studies are released from resin-based dental materials, and additional studies on the safety of these materials are warranted. As new resin materials are developed, a combination of toxicological, endocrinological, and epidemiological studies should monitor their safety and their potential to be exposure sources of endocrine-disrupting chemicals.