Putting BPA-based dental fillings in perspective

Small effects could have a big social impact, but mechanisms of any bis-GMA neurotoxicity remain elusive

A new study finds that children who have their cavities filled with a white composite resin known as bis-GMA appear to develop small but quantifiable drops in psychosocial function. To put it simply: Treated kids can become more moody, aggressive and generally less well adjusted.

Bis-GMA is hardly a household name, although its starting ingredient — bisphenol A — is. An estrogen-mimicking compound, BPA is best known as a building block of some clear plastics, food-contact resins and inks used for store receipts.

The new report, posted online July 16 in Pediatrics, is “very important,” says Philip Landrigan, director of the Children’s Environmental Health Center at Mount Sinai School of Medicine in New York City. These data linking bis-GMA and behavioral changes in kids “make a strong case that in the short term, use of BPA-containing dental materials should be minimized,” he says. Over the longer term, he argues, manufacturers should look to discontinue the materials’ use in children as soon as acceptable substitutes are readily available.

In the new study, researchers followed more than 400 youngsters with cavities after each received his or her first-ever fillings. Throughout the next 5 years, the scientists linked a subtle drop in behavioral scores to cavities that had been filled with a composite material made from bis-GMA.

The numerical change in behavioral scores was small, roughly 2 to 6 points on a 100-point scale (where a score of 50 is average). Parents might not notice a change that small or could easily attribute it to other factors. But that doesn’t mean the magnitude was trivial, argues Nancy Maserejian of New England Research Institutes in Watertown, Mass., who led the study.

A 1- or 2-point drop in IQ is similarly small. But if it occurred across a broad swath of a huge population, even such a tiny change would prove costly. Each 1 point drop in IQ will diminish an individual’s lifetime earnings potential — and even, potentially, boost community costs for education and dealing with behavioral and learning problems. Similarly, each drop of a few points in neurobehavioral measures effectively shifts huge numbers of children below the threshold of being able to effectively manage stress, anger, disappointment and relationships with family and others, Maserejian notes.

But here’s a caveat: Her team’s new study only offers a rough gauge of children who might be maladjusted. The researchers never administered clinical diagnostic behavioral tests to the children, who were 6 to 10 years old at baseline. Instead, they periodically administered some widely used checklists to the children or their parents, allowing each to self-assess features such as a child’s attitudes toward teachers or others, depression, self-esteem, attention problems, delinquent behaviors, acting out or problems with attentiveness.

Children who scored poorly, as measured by a certain threshold value, should be referred for a full-scale diagnostic work-up by a clinician, Maserejian explains. But any scores from such followup diagnostic assessments were not part of her team’s current study.

Despite these qualifications, the new work constitutes a “highly credible study by a superb group of investigators,” Landrigan says.

No ‘clean bill of health’
That’s high praise from someone who has more than a little familiarity with the field.

In an October 2010 paper in Pediatrics, Landrigan’s group reviewed the safety of bis-GMA resins and related alternatives. These researchers concluded that bis-GMA appeared preferable for use in treating kids’ teeth when compared to a related BPA-based material known as bis-DMA.

“We did not give bis-GMA ‘a clean bill of health,’” Landrigan notes. In particular, his group did not address neurodevelopmental impacts, he points out, because they reviewed only published data. And two years ago: “[T]here were no published studies in the medical literature that examined this question.”

The new data “are not inconsistent with our findings” that dentists continue to use BPA-based sealants (as opposed to fillings), Landrigan says. Sealants help prevent cavities and children receive only a short term exposure to BPA during treatment. However, his team recommended that dentists minimize exposure to BPA resins in pregnant women and that manufacturers begin developing alternatives “with less estrogenic potential.”

Based on the new study, which “credibly finds a neurodevelopmental effect associated with use of BPA-containing dental materials,” Landrigan now argues that his earlier recommendations deserve “reconsideration” as being too mild.

BPA: A red herring?
Landrigan’s apprehension appears based on concerns about the hormonal alter ego of BPA. However, “there’s controversy as to whether bis-GMA based materials release meaningful amounts of BPA it in the mouth over time,” Maserejian says. “We didn’t measure BPA,” she adds, nor any other breakdown products of bis-GMA.

In a study now underway, these researchers are doing just that. But for now they can’t say whether BPA should be indicted for the effects her team has just reported.

Jeffrey Stansbury strongly suspects it shouldn’t. Associate dean for research at the University of Colorado School of Dental Medicine in Aurora, he notes that the any BPA-based compounds used in dentistry do not contain BPA. They start with BPA, but then alter it by adding additional chemical features that make the new product resistant to breaking down again into BPA.

So if there is a true link between bis-GMA fillings and neurobehavioral changes in kids — and this polymer chemist doesn’t question that there might not be — he suspects such problems would trace to other compounds. Some of these may be additional BPA derivatives.

Real solution: Prevention
Clearly, Stansbury says, more research is urgently called for. But he asks the public not to panic. Troubling as the new findings are, they point to small changes and risks. “I wouldn’t want parents to avoid taking their kids to the dentist over this because there are much more significant health risks from tooth decay than there are from small exposures to these [composite resins].”

He professes “no qualms” about having bis-GMA or related composite resins used in his kids’ mouths. For now, the data do not suggest the cure is worse than the disease, Stansbury says.

But to Maserejian, the real bottom line from her data should be a renewed emphasis on fighting tooth decay. Because by preventing cavities, families obviate any need to choose between even mildly toxic dental treatments.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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