Over the past two decades, the share of children with defective tooth enamel has been rising. And BPA, a chemical used to make many plastics, could be partly to blame. That’s the finding of a new study in rats. It showed that this pollutant can trigger the same problem in lab animals that had been showing up in the kids.
Enamel is the hard substance that covers a tooth. If it does not form properly, a child can develop cavities and other problems. A dentist can repair these defects. But there is no way to fix the altered gene instructions responsible for making the enamel weak in the first place.
This enamel defect “now affects 15 to 20 percent of children six to nine years old,” says Sylvie Babajko. She is a molecular biologist at INSERM. It’s the National Institute for Health and Medical Research in Paris, France. This defect affects different numbers of children in different places. In some parts of the world, as many as 40 percent of children may have this weakened enamel, she notes. But where it’s been studied well, about 1 in 6 kids (18 percent) are affected.
Babajko, Katia Jedeon and their team are studying this failure of kids’ tooth enamel to form correctly. The problem affects both molars and incisors (teeth in both the back and front of the mouth). The teeth end up with white milky spots. They are caused when the mineral structure of the teeth develop weakened regions. These are defects.
The problem develops when teeth are first forming, Babajko notes.
The problem is not new. But it has been showing up in more and more kids. And the increase emerged at the same time as did other health problems linked to a specific group of chemicals, she notes. Such chemicals are known as endocrine disruptors.
In their new study, the researchers traced the weakened enamel in their rats to pollution-altered genes. Those genes instruct cells on how to build a tooth. Babajko’s group reported its findings on May 31 at the 18th Congress of European Endocrinology. It was held in Munich, Germany.
Confusing the body’s hormone system
Hormones are part of the body’s endocrine (EN-doh-krin) system. They control the timing of pivotal actions — from how organs form and how cells use energy to how the brain works and how the body prepares for reproduction. In some cases, pollutants can block or slow the action of hormones. Other times, these pollutants can masquerade as hormones. Either way, these endocrine disruptors can do a lot of damage by throwing off the timing of when the body turns important actions on or off.
Two types of hormones — estrogens and androgens — play a role in directing the cells that make tooth enamel. Estrogens are known as female sex hormones. Androgens are male sex hormones. Both types of hormones play important roles in how the bodies of all young mammals develop. Their effects start in the womb and continue on through puberty and adulthood.
Over the past few years, Jedeon and her colleagues found evidence that two pollutants could promote defects in enamel. Both were androgen disruptors.
One chemical was vinclozolin (Vin-KLOH-zuh-lin), a fungi-killing chemical. It can block the action of the androgen known as testosterone. But aside from farm workers, most people don’t encounter this chemical.
The other pollutant, BPA, is far more common. Short for bisphenol (Bis-FEE-nawl) A, this chemical can mimic the action of estrogen. It also can disrupt the action of testosterone. Manufacturers use BPA to make everything from eyeglasses and kitchen bowls to dental sealants. A coating on many papers, BPA rubs onto hands from the paper used to print many store receipts. BPA also coats the inside of many food and drink cans and jar lids. Some 16,000 different food and drink products use BPA in their packaging. Most people have broad exposure to this chemical.
Although the INSERM studies had linked exposures to both chemicals with impaired enamel formation, the researchers did not know precisely what was going wrong. So for their latest study, they decided to home in on genes of enamel-making cells.
Of genes and androgens
Kids may be most vulnerable to BPA very early in life, Babajko says. This would be from when their baby teeth first begin to form until about age four or five. So for its new study, Babajko’s team exposed pregnant rats to either BPA or vinclozolin. Once the babies were born, those pups were exposed for another month. The researchers then examined cells and their genes in those pups.
BPA and vinclozolin both altered a small group of genes, the data show. These genes are directly involved in the enamel-making of teeth. What’s more, these genes are especially vulnerable to changes in androgens. As a result, Babajko now concludes, BPA and such androgen-disrupting chemicals may be “leading to the weakening of enamel quality.”
The results also suggest these tooth defects could be used as a signal that a child has been exposed to a hormone-disrupting chemical, she adds.
Many cells and body parts that these chemicals might affect have not yet been studied, says Andrea Gore. This is because they’re not usually considered to be part of the endocrine system, she explains. Gore is an endocrine expert at the University of Texas at Austin. The new study, she says, suggests that hormone-disrupting chemicals may be affecting parts of the body that have not yet been studied for these effects.
“Teeth certainly fall into that category,” she says. If tooth development involves these hormones, then they may be vulnerable to impacts from chemicals like BPA, she says.
Frederick vom Saal studies hormone-mimicking pollutants such as BPA at the University of Missouri in Columbia. Androgens and estrogens are involved in how the body uses calcium to make bone, he explains. Similar processes are involved in producing tooth enamel. So it is possible that a hormone-disrupting chemical such as BPA could disrupt enamel-making in teeth. And the cells Babajko’s study examined do interact with such hormones, he adds.
“One of the things we know about these [hormones] is that they are involved in all kinds of stuff you wouldn’t necessarily expect,” says vom Saal. What’s more, these hormone-mimicking pollutants can affect people and lab animals in very similar ways. So, what was seen in this study could “point us to [the cause behind] something that is a significant public health issue for a substantial number of children,” he says.
It is not yet possible to know for sure if BPA is responsible for weakened tooth enamel and resulting cavities. But scientists say that there is enough evidence to make further research important.