Exposure to high amounts of lead is likely one cause of the high rates of tooth decay found among certain groups, such as children raised in the inner city, according to a study in rats by University of Rochester dental researchers published in the September issue of Nature Medicine.
The scientists say that while lead does not actually cause cavities, it appears to make rats -- and thus people, whose teeth get cavities in an identical manner -- much more susceptible.
"This is one more compelling reason to get lead out of the environment," says lead investigator William Bowen, Margaret and Cy Welcher Professor of Dental Research and the founder of the Rochester Caries Research Center, the nation's first research center on tooth decay. Also working on the project were Gene Watson, assistant professor of clinical dentistry; graduate student Bianca Davis; Richard Raubertas, associate professor of biostatistics; and technician Sylvia Pearson.
Lead is well recognized as causing developmental and other problems. While lead has been removed from most gasoline, it's still present in old paint and commonly in soil or dust around contaminated buildings. Bowen says that the areas with the highest lead pollution -- inner cities and the Northeast -- mirror areas where dentists see the highest rates of tooth decay.
The team studied cavity susceptibility in rats born of mothers exposed to lead compared to offspring of rats not exposed to lead and found that offspring from exposed rats had 40 percent more cavities. The study, funded by the National Institute of Dental Research (NIDR), is the first to document the link between lead exposure and high cavity rates that a few small epidemiological studies have suggested.
The team is now searching for the cause. Some studies have suggested that lead interferes with the development of teeth. In humans lead is stored in the bones for decades, and higher amounts than normal are released into the blood of women who are pregnant. These high levels reach the fetus at a time critical to the development of teeth and salivary glands. The scientists discovered another possibility: They found that pups of exposed rats produced 30 percent less saliva, which protects teeth against cavities by neutralizing acids, providing minerals, and in many other ways. In addition, they detected levels of lead in the mothers' milk that were 10 times higher than the lead levels in their blood.
In an accompanying article in the journal, dentists Martin Curzon and Jack Toumba of the Leeds Dental School in the United Kingdom say this is the first time that scientists have pinpointed breast milk as a likely route of lead transfer from mother to offspring, and that reduced saliva flow has been implicated as a likely mechanism of decay in lead-induced cavities.
"Lead is not something that most dentists think of when they talk about the causes of cavities, but they should," says Watson. Poor hygiene, lack of dental care, and poor diet are still major concerns of dentists, as they should be, says Bowen. But he suggests that dentists who treat children from areas of high lead pollution should consider boosting standard preventive measures: fluoride treatments, check-ups, healthy diet, and dental sealants.
Lead is likely one reason why dental cavities are still a major problem in some pockets of the population despite the widespread use of fluoride and fluoridated toothpaste, Bowen says. While about half of 12 year olds in the U.S. are now free of cavities, 80 percent of the cavities in the group are seen in just one-fifth of the children. Ninety-five percent of all adults in the U.S. have cavities, which are a leading cause of tooth loss.
"There's a feeling among some people that dental caries is licked, that it's no longer a problem," says Bowen. "The fact is that it is still a serious public health problem in the U.S. and throughout the world."
Journal
Nature Medicine