Caries: Legacy of mom's lead exposure?

Several studies have linked a high incidence of dental cavities to lead exposure, offering parents yet another reason to shield their youngsters from old house paint and other potential sources of this toxic heavy metal. However, a new animal study now suggests that for some of these children, one of the more potent sources of lead -- and caries vulnerability -- may be all but unavoidable: their mother. 

 Throughout the United States in recent years, "there's been a big drop in the prevalence of childhood caries," notes William H. Bowen, a dentist and microbiologist at the University of Rochester (N.Y.) School of Medicine and Dentistry. Of those cases that do show up, however, "some 80 percent are occurring in just 20 percent of kids" -- mostly those living in inner cities, where lead exposures can still be relatively high, he observes.

 Because lead mimics calcium, the body normally stores most lead in bone. During pregnancy and lactation, when the body breaks down bone to liberate calcium for the developing young, lead can be released back into the blood. "We know that lead crosses the placenta," Bowen says, "so there was good reason to suspect it could affect [tooth] development." His group decided to probe maternal transmission of lead in pups born to female rats that had been raised on drinking water spiked with relatively high concentrations of lead (34 parts per million). Resulting blood concentrations, about 40 micrograms per deciliter, are at the high end of what can be found in humans.

 In the September Nature Medicine, the researchers report that pups from lead-exposed moms developed 40 percent more dental cavities and produced 30 percent less saliva than did those born to mothers raised on leadfree water.

 The two observations may be related, the Rochester scientists note. Saliva not only helps wash away food particles that might contribute to the development of caries but also possesses natural antibiotics to retard the growth of bacteria. Saliva can even supply teeth with the mineral building blocks needed to repair incipient cavities.

 Moreover, the Rochester study turned up evidence that moms may remain an important conduit for delivering lead after birth. "We found surprisingly high levels of lead in [breast] milk," Bowen says -- concentrations roughly 10 times as high as those in the mothers' blood. "This indicates that there is clearly some concentrating mechanism" in mammary tissue, he says.

 Previously, there had been a suspicion that any lead-induced vulnerability to decay traced to a substitution of the metal for calcium or some other constituent in tooth enamel, creating weaknesses in its crystalline structure, say Martin E. J. Curzon and K. Jack Toumba of the University of Leeds School of Dentistry in England in an accompanying commentary. The primary exposures of concern had been lead-based paint and drinking-water pipes.

 Now, the Rochester findings "reveal two hitherto unrealized aspects of lead toxicity," they observe -- the role of lead stored in the mother's body and the salivary glands' vulnerability.

 These new data may even have some historical implications, the Leeds pair muses. While some toxicologists have suggested that IQ declines associated with drinking water from lead pipes may have contributed to the fall of the Roman Empire, Curzon and Toumba offer an alternative speculation. Perhaps, they say, chronic toothaches "afflicted the Roman legions, rendering them incapable of defending the Empire."