Estogenic agents leach from dental sealant.

For 30 years, dentists have used a class of plastic resins to seal teeth from decay-causing bacteria and to help repair teeth that have developed cavities.

Now, a new study reports that significant quantities of bisphenol A, a chemical building block of these resins, can leach into the saliva of treated patients.

In the body, this chemical can emulate the female sex hormone estrogen.

Exposure to estrogenlike agents-especially during fetal or early postnatal development-can trigger gender-bending changes (SN: 7/15/95, p. 44) or reproductive havoc (SN: 1/22/94, p. 56). They may also foster cancer in reproductive organs such as the breast (SN: 7/3/93, p. 10).

Researchers at the University of Granada in Spain applied about 50 milligrams of a bisphenol-A-based dental sealant to the molars of 18 college-age volunteers. The scientists then hardened the material using a curing process that links individual molecules of bisphenol A into a chainlike polymer.

Because studies by others had shown that such curing fails to harden all of the bisphenol A, the Granada group looked for leaching of this chemical or of small, partial chains known as bisphenol A dimethacrylate. They took saliva from each of the volunteers before and 1 hour after they had been treated and compared the samples.

In the just-published March Environmental Health Perspectives, Nicolas Olea and his coworkers report finding between 90 and 931 micrograms of bisphenol A in the roughly 30 milliliters of saliva obtained from each person after, but not before, treatment. The researchers also found some dimethacrylate in the saliva of three volunteers after treatment. The scientists then confirmed the estrogen-mimicking ability of bisphenol A and dimethacrylate in a test of human breast cancer cells.

"This study seems very well done and well controlled," says Jack L. Ferracane, chairman of biomaterials and biomechanics at Oregon Health Sciences University in Portland. However, while he observes that "we don't know a lot about these resins," he says the leaching of bisphenol A here "seems at odds with other studies, which don't show this [leaching]."

Though some of the never-cured molecules "will come out," he acknowledges, "that happens relatively quickly and doesn't provide a constant source of exposure." So "the seriousness of this issue seems limited," he concludes.

"It's premature to say that," counters endocrinologist Ana M. Soto of Tufts University School of Medicine in Boston, a coauthor of the new study. "We have some evidence that bisphenol A is still leaching after 2 years." To determine how common long-term leaching is, her group has collected 6-month follow-up samples of saliva.

Soto notes that dental resins also wear away in time and are ingested. While there are no data on how much of this material crosses the stomach lining and enters tissues, "this is something that should be studied," she maintains.

Frederick S. vom Saal of the University of Missouri-Columbia agrees. Though the Granada study indicates that it takes 10,000 times as much bisphenol A to elicit the same effect in human cells as the body's natural estrogen, his work indicates that such cell culture studies underestimate the potency of this estrogen mimic.

Much estrogen in the body is bound to blood proteins and cannot enter cells.

Vom Saal's recent experiments with cells in culture suggest that bisphenol A does not bind to these proteins as well as estrogen does. So proportionally more bisphenol A would be available to interact with cells.

"Our studies show that estrogens operate at a trillionth of a gram per milliliter of blood," he says. The bisphenol A measured in saliva during the Granada study is "100 million times higher than the amount of estrogen that is biologically active in the human fetus." But as yet there is no indication of how much bisphenol A in saliva would actually enter the blood.

Although fetuses are unlikely to be exposed to bisphenol A, vom Saal worries that such environmental hormones might cause serious, irreversible problems during other periods of development, including puberty.

Indeed, he says, based upon the amounts of bisphenol A being reported by Olea's group, "I would be concerned about the possibility of high levels of this chemical getting into a child. And until we learn more about its biological effects, as a parent I would therefore err on the side of caution" when it comes to using dental sealants.