Passive smoking may foster kids' cavities. (Infectious Diseases).

Young children who grow up in an environment where people smoke face an exaggerated risk of dental decay--but only in their baby teeth, a new study finds.

Earlier studies had demonstrated that environmental exposure to cigarette smoke can weaken the immune system and promote the growth of decay-causing bacteria. Because the enamel on baby teeth is very thin, young children should be especially vulnerable to smoke's effects on teeth, reasoned pediatrician C. Andrew Aligne of Pediathink, a Rochester, N.Y.-based childhealth research group.

He and his colleagues investigated that hunch by reviewing dental and health records of nearly 4,000 U.S. children between the ages of 4 and 11. All participated between 1988 and 1994 in the Third National Health and Nutrition Examination Survey.

When surveyed, more than 90 percent of the children still had at least one baby tooth and 76 percent had acquired at least one permanent tooth. Slightly more than half of the children also had residues of a nicotine-breakdown product in their urine, indicating regular exposure to cigarette smoke. These data enabled Aligue's team to compare the youngsters' tooth decay and probable amount of smoke exposure.

Cigarette smoke didn't affect the number of cavities and fillings in a child's permanent teeth. However, after accounting for other known risk factors, the researchers did find evidence that in baby teeth, some 27 percent of unfilled cavities and 13.7 percent of fillings could have been avoided if all of the children had been shielded from exposure to cigarette smoke. The scientists report their findings in the March 12 Journal of the American Medical Association.--J.R.