A new study says children exposed to passive smoke are more likely to develop cavities, but skeptics say that before anyone jumps to conclusions, scientists should take a look at their fluoride levels and how many cavities their parents have.

"It's a pretty novel idea that no one's looked at before in the U.S., " says Dr. Andrew Aligne, assistant professor of pediatrics at the University of Rochester's Strong Children's Research Center and lead author.

The research team analyzed data on more than 3,800 children, age 4-11, who had been tested for levels of cotinine in the blood. Cotinine is produced when the body tries to excrete nicotine and is a way of telling how much tobacco smoke exposure someone has had. The children were enrolled in the Centers for Disease Control and Prevention 's third National Health and Nutritional Examination Survey (NHANES III).

"We plotted a graph with the number of cavities per child vs. the average cotinine level, and there appears to be a dose response, suggesting a biological gradient, which argues for a causal relationship," says Aligne.

Aligne found 47 percent of the children in the study had cavities in their baby teeth, while 26 percent had decay in their permanent teeth. The larger numbers in baby teeth make sense, he says, since younger children spend more time with their parents, increasing exposure to passive smoke.

Although it might be assumed more cavities would show up in the children of poor parents, he emphasizes the link between cotinine levels from second-hand smoke and cavities was still valid even after taking such variables as age, sex, race, region, dentist's visits, nutritional status and blood lead levels into account.

"We separated out the information on decayed teeth and cavities vs. fillings," says Aligne. "The passive smoking related to decayed teeth … there wasn't a huge difference between poor and non-poor, in cavities."

One shortcoming of the data, Aligne says, is "we don't have information about tooth brushing habits. People may say that parents who smoke are parents who don't take care of their kids' teeth."

The smoke-cavity link makes perfect sense, however, says Aligne, based on recent research.

"Caries [cavities] are thought to be an infectious disease, which need germs in the mouth to cause it. Recent studies have shown that nicotine in vitro [in a test tube] will increase the growth of the same germs that are involved in making cavities."

Saliva helps wash away disease-causing organisms, so that having too little of it, "dry mouth," also increases cavities. "Anything that causes dry mouth, such as passive smoking, will do that because it causes upper respiratory inflammation. Kids who are exposed to passive smoking may have allergies or asthma and be on antihistamines," increasing mouth dryness, he says.

However, Donna Mager,, dentist-scientist in the department of oral biology and specialist in oral medicine, at The Forsyth Institute in Boston says, although fascinated by the study's results, she's skeptical.

"There are a couple of things I'd want to know. What is the fluoride level in these children? Fluoride levels make a huge impact on the caries experience. Sixty to 75 percent of caries can be eliminated if the fluoride levels are high," she says.

Mager says before linking smoke and cavities, she'd like to see more data on the amount of plaque and its composition, as well as how many cavities the parents have.

"There is vertical transmission of bacteria from caretaker to child. If the parent is experiencing high caries-producing organisms in the mouth, children would also have high levels of the organism," she says.

Mager says, however, she applauds the study for investigating the possible link, adding, "it's hard to look at large numbers of children and to look at all the factors."

The study is being presented this week at the Pediatrics Academic Societies meeting in Baltimore.

What To Do

"It helps put into context that these results don't seem so far-fetched, and gives us one more reason to protect children from tobacco smoke," says Aligne. And, "another implication might be for dentists and dental care professionals who may not do any kind of counseling around passive smoking, to include that along with talking about candy."

Help your kids have healthy teeth and gums with these tips for parents from the American Dental Association.

Do it for your kids -- and yourself. Quit smoking with help from the office of the surgeon general.

For more HealthScout stories on second hand smoke, click here.