These findings indicate that exposure to bisGMA-based dental composite resins may impair psychosocial health in children. With increasing level and duration of exposure to bisGMA-based composite over 5 years of follow-up, children reported more anxiety, depression, social stress, and interpersonal-relation problems, and were more likely to have clinical-range scores for parent-reported total problem behaviors. No similar associations were found for amalgam permanent tooth exposure levels or in the previously reported23
intent-to-treat randomized group analysis; thus, unmeasured/unknown confounding by factors associated with severity of dental disease on perma-nent teeth is unlikely to explain our findings for bisGMA-based composite. UDMA-based polyacid-modified composite (compomer) had no associations with psychosocial function scores.
Owing to the lack of relevant biomarker data in NECAT, we were unable to examine whether children with greater composite exposure had increased concentrations of potentially leached monomers, such as bisGMA, or BPA, which may plausibly cause the observed associations. Thus, it remains unclear whether our observed associations are attributable to BPA or to some other chemical component of the composite intervention. Numerous studies of the applied composite (Z100) have shown that it released BPA, bisGMA, bisDMA, and/or BPA diglycidylether,18,19,25–27
including 1 study of 19 children showing that urinary BPA levels remained elevated 14 days after treatment.28
Other bisGMA-based resins may have similar properties. In a cross-sectional study, Korean children with >10 resin-composites (unspecified manufacturers) had urinary BPA levels on average 2.7 µg/g creatinine higher than those with no fillings.34
A recent meta-analysis concluded that, in the worst-case scenario, a full-crown posterior bisGMA-composite restoration might release 132.36 µmol after 24 hours, or on average 57.38 nmol, and that resin-based dental materials may contribute substantially to BPA exposure.6
Compared with bisGMA-based resins, UDMA-resins have little or no effect on BPA exposure.27,29,35
As new materials (eg, ormocer-based, silorane-based) are developed, thorough toxicological testing, including data on the long-term release of components, should be a requisite.
NECAT did not collect data on other common BPA exposure sources, such as consumption of canned foods/beverages, polycarbonate plastic container use, and thermal-receipts handling; however, the previously reported intent-to-treat findings were based on randomized treatment plan,23
and randomization led to balance in most characteristics, including bottled versus tap water use and socioeconomic status, which may indicate BPA exposure. Randomization should also have accounted for methacrylate exposure from sealants, which were offered to all NECAT participants for caries prevention. In the current nonrandomized exposure analysis, the findings for bisGMA-based composite remained robust in multivariable models.
Our finding that cumulative exposure to composite on posterior-occlusal (chewing) surfaces was most strongly associated with poorer psychosocial outcomes supports the hypothesis that long-term release of resin components caused these associations. In NECAT, cumulative exposure to amalgam restorations on posterior-occlusal surfaces (versus all surfaces) was more strongly correlated with urinary mercury concentrations, well after the initial placement of amalgam.22
Studies have shown that chewing increases the release of mercury from dental amalgam.36,37
Composite restorations have decreased longevity compared with amalgam, and, as shown in previous analyses of NECAT, posterior composites underwent more repairs or replacements.17
Thus, it is plausible that the combination of mechanical and chemical/enzymatic degradation, exacerbated by chewing on posterior-occlusal surfaces, promotes the release of chemicals from composites throughout the life of the restoration.
Although both the BASC-SR and CBCL are validated and widely used in clinical and research settings, we found fewer significant associations by using the CBCL than using the BASC-SR. These differences may be because of distinctions in the scales or their administration. The BASC was derived conceptually, considering clinically relevant material, rather than the more empirically derived CBCL. BASC anxiety and depression scores have been associated with greater gestational BPA exposure among girls in early childhood.15
In NECAT, the BASC was self-reported, whereas the CBCL was parent reported. A longitudinal study spanning 24 years showed that when there are multiple informants for psychosocial assessment, informant-differences in rating internalizing problems become greater as children get older, and overall, children/adolescents typically self-report more internalizing and externalizing problems than obtained by parent/teacher report.38
Thus, it is possible that that self-report by NECAT participants (aged 11–16 years at follow-up) more accurately reflected their psychosocial problems; however, the discrepancy between the BASC-SR and CBCL necessitate additional studies to confirm our results.
Our observed effect sizes, within the SD of both psychosocial instruments, nevertheless may indicate clinically meaningful consequences at both the individual and population levels. Shifting the mean value of psychosocial function scores in a population, even by a modest amount, will predictably produce a large change in the prevalence of clinical cases.39,40
This analysis found clinically significant scores were 2 to 4 times more common among children with higher composite exposure. Generally, unexposed children tended to be similar to those with low-moderate exposure, which is expected because randomization presumably balanced genetic and other primary contributors of psychosocial functioning.
In conclusion, greater exposure to bisGMA-based dental composite, but not UDMA-based polyacid-modified compomer, was associated with impaired self-reported psychosocial function in children. Given that most children received both compomer and composite, additional studies that randomize participants to only 1 type of material are warranted. Nevertheless, the current findings were strong in magnitude, highly statistically significant, and robust in sensitivity analyses. A causal association between bisGMA-based composite and psychosocial health is supported by (1) the previously reported randomized “intent-to-treat” results,23
(2) lack of associations with amalgam permanent tooth exposure levels, and (3) lack of self-selection to restorative material. Together with a separate National Institutes of Health–funded randomized trial among Portuguese children,21
these trials definitively showed that among children aged ≥6 years, through 5 to 7 years of follow-up, amalgam did not adversely affect neuropsychological measures, whereas bisGMA-based composite was associated with poorer psychosocial outcomes and required more replacement and repair. Thus, there is no evidence to support that clinicians should systematically remove amalgam in posterior teeth to replace with bisGMA-based composite. Given the potential risks and decreased durability of composite, combined with transient increases in plasma mercury concentrations resulting from amalgam removal,41,42
such procedures might carry more risk than benefit. Longitudinal trials are needed to examine modern-day resin-based dental materials for the long-term release of their components and health effects.