Effects seen only for fillings that used bis-GMA, a resin derived from bisphenol A

By Janet Raloff

Web edition: July 16, 2012

A resin in the most commonly used white composite dental fillings may be linked to subtle neuropsychological deficits in children.

The association appears in reanalyzed data collected from 434 children as part of a trial begun roughly a decade ago. The original study was designed to probe for IQ or other neurobehavioral impacts of the mercury that can be released by metal-amalgam dental fillings. Half of the kids received amalgam fillings for cavities in back teeth, the rest got composite back fillings.

Cavities in front teeth always got composite fillings. Wherever composites were used, baby teeth got a urethane-based resin, while permanent teeth got a resin called bis-GMA that is derived from bisphenol A, or BPA. BPA can mimic the hormonal activity of estrogen and exposure in the womb has been linked to behavioral changes in mice and young children.

The 6- to 10-year olds were then followed for five years, with the children or their parents periodically participating in assessments of a kid’s mood, behaviors (including aggression), attitudes at school and interpersonal relationships.

That original study, published in 2006, turned up no problems associated with metal fillings. But the research did hint that composite fillings might be worrisome. After reanalyzing their data, the researchers now find that children receiving bis-GMA fillings did exhibit low-level changes on behavioral assessments.

Measured changes were small, perhaps 2 to 6 points on a 100-point scale — and most strongly associated with higher exposures and with fillings in back, which are subject to the most wear and tear during eating, the researchers report online July 16 in Pediatrics.

"The findings are believable, and they make a strong case that in the short term use of BPA-containing dental materials should be minimized, and in the longer term that use of these materials should be discontinued entirely as soon as acceptable substitutes are readily available," says Philip Landrigan, a professor of pediatrics at Mount Sinai School of Medicine in New York City.

The suspicion is that something might be leaching out or breaking off of these fillings, notes epidemiologist and study leader Nancy Maserejian of New England Research Institutes in Watertown, Mass. To test that idea, her team has just begun a trial that will monitor urine from children newly treated with bis-GMA fillings for at least 6 months, scouting for BPA or other breakdown products.

“A lot of these [neurobehavioral] measurements have thresholds for identifying a clinically significant or at-risk type of problem,” notes Joseph Braun of the Harvard School of Public Health, who was not involved in the new study. Disturbingly, he says, scores on these assessments were changing among the kids with the most bis-GMA exposure — “to where some are crossing the threshold.”

Although the initial inclination might be to suspect BPA is responsible, there’s no support for that here, says Jeffrey Stansbury, a biomaterials engineer at the University of Colorado School of Dental Medicine in Aurora. Studies by others have shown that when dental materials made from bis-GMA degrade, “they don’t break down to BPA,” he says. However, he adds, that doesn’t mean that some other constituent isn’t triggering behavioral changes. “So this material’s association with early childhood behavior is certainly worth following up.”