Taking children to the dentist is rarely a stress-free experience, but it may soon become a more fraught ordeal.

For decades, parents concerned about filling their kids's cavities with mercury-laced amalgam have opted instead for white composite: modern, metal-free, practically invisible. Demand has increased dramatically since the 1960s, when the materials were first introduced—and today, more than 10 million American children receive the filling every year. But according to a new study in the journal Pediatrics, a common composite formula may be placing kids at slightly higher risk for anxiety and depression.

Composite fillings are typically made of glass or quartz mixed with resins and adhesives. But these materials, while approved by the Food and Drug Administration, have not been studied for long-term health effects.

In today's study, funded by the National Institutes of Health, children with a popular composite filling known as bisphenol-A-glycidyl-methacrylate (Bis-GMA) displayed worse scores on scales of “psychosocial” well-being up to five years after treatment, compared to kids who received silver amalgam fillings or a composite made with different materials. Children exposed to the most Bis-GMA fillings for the longest periods of time were two to four times more likely to report “at risk” psychological problems requiring medical help. The association was strongest for kids with cavities filled in the back molars, where the composite can break down and possibly enter the bloodstream.

Parents may be particularly interested to know that one of the composite filling's ingredients, bisphenol A, commonly known as BPA, has drawn scrutiny in recent years because of its ability to act as an estrogen in animal lab studies. Thanks to its ubiquity in canned foods, sodas, and common plastics, the chemical courses through the bloodstreams of 93 percent of Americans tested, according to the Centers for Disease Control and Prevention. In 2010, the FDA declared the substance safe at low levels, though the agency noted “some concern” due to possible effects of BPA on the brain and behavior of fetuses, infants, and children. Some manufacturers have removed BPA from consumer products such as baby bottles and water bottles.

BPA remains a common additive in both dental fillings and dental sealants, according to the American Dental Association. Through a statement on its website, the organization maintains that BPA used in dentistry is safe, and that a child is exposed to it on a limited basis during the filling procedure itself. “The estimated one time exposure (upon sealant placement) for a male child of median body weight (51 to 112 pounds) is approximately 5.5 micrograms, which is two to five times lower than the estimated daily exposure from food and environmental sources,” said the statement. Few studies have examined how much BPA may be breaking down from the filling material over time.

The study in Pediatrics did not look at how much of the chemical was present in the bodies of the 534 children evaluated. “We didn’t measure BPA here at all, and we don’t know why or how dental materials are causing an association if indeed it is causal,” said the study’s lead author, Nancy N. Maserejian of the New England Research Institutes. “There are other ingredients in the composites, too, and many of these have not been studied,” she added.

So what’s a parent to do? Is it time to rip out the composites and embrace the 140-year-old technology of metal fillings all over again? After all, those last longer—up to 30 years—and are also deemed safe for children by the FDA.

Not yet. “The main thing to take from this is that more research is needed,” said Maserejian. She said she will not shy away from Bis-GMA if it is deemed the best filler for a particular cavity by her childrens’ dentist. She also explained that the overall difference in psychological scores—2 to 6 points on a scale of 100—“is very small and probably isn’t noticeable in an individual.” However, considered at the population level, a downward shift in scores could mean a modest uptick in children at risk for developing clinical symptoms of mental health problems. “On a public health level it could have an impact,” she said.

More than half the children in the U.S. have cavities by the age of 7, and more than 80 percent have them by adolescence. In recent decades, composite materials have greatly improved in durability, lasting on average five to 10 years in a cavity space, according to Mary Hayes, a Chicago-based pediatric dentist and spokesperson for the American Dental Academy.

The best strategy, said Hayes, is not to get the cavities in the first place. “I’m going to use this study as another educational opportunity,” she said. “The best tooth material is your own.”