When Karen Rice, of Aston, Pennsylvania, took her 4-year-old son, Luke, to the dentist for a checkup, she was shocked: He had a large cavity in one of his molars. Soon afterward, Luke complained that his teeth hurt, and the dentist found three more cavities between his teeth. "One was so big that the tooth got infected and had to be pulled," says Rice, who's endured five root canals herself.
Parents often assume that kids get cavities because they're lax about brushing and flossing. That's true to an extent, but what few people know is that tooth decay is a disease known as dental caries that's caused by specific germs, spreads easily within families, and can last a lifetime. What's more, it's more common among young children than any other chronic illness, including asthma and diabetes.
At least 4 million preschoolers suffer from tooth decay -- an increase of more than 600,000 kids in the last decade. "Children now have much more sugar in their diets at an early age," says Paul Casamassimo, D.D.S., professor of pediatric dentistry at the Ohio State University College of Medicine and Public Health, in Columbus. And the popularity of bottled water -- which usually doesn't contain fluoride -- may also contribute to the growing problem, he says.
Tooth decay begins with a group of germs called mutans streptococcus. "The bacteria feed on sugar and produce acid that eats away at the structure of teeth by depleting calcium," explains Parents advisor Burton Edelstein, D.D.S., founding director of the Children's Dental Health Project. The bacteria also create plaque -- a yellowish film that builds up on teeth and contains even more enamel-eroding acid. Once an area without calcium becomes big enough, the surface of the tooth collapses, and that's a cavity.
Babies are born without any of these harmful bacteria in their mouth, and studies have proven that moms (rather than dads) typically infect their children before age 2. It happens when you transfer your saliva into your child's mouth -- by repeatedly eating from the same spoon as your baby, for example, or letting your toddler brush his teeth with your toothbrush. And if you've frequently had cavities yourself, you're particularly likely to pass the germs along. Once a child's mouth has become colonized with mutans, he'll be prone to cavities in his baby and permanent teeth that can cause pain and difficulty eating. "It's an old wives' tale that 'soft teeth' run in families, but what's really passed along in families are high levels of decay-causing bacteria," says Dr. Edelstein. In fact, 80 percent of all cavities occur in just 25 percent of kids. The key role that bacteria plays in decay may also explain why some kids who eat tons of candy or never floss are lucky enough to avoid dental problems.
Emilie Mosby, of Kingman, Arizona, had lots of cavities when she was a kid, so she panicked when she saw a dark spot on her 3-year-old daughter's tooth. "I took Teagan to the dentist, and when he told me she had a cavity, I almost cried," says Mosby. "It's so frustrating. I've always tried to take good care of her teeth, and I have a friend who doesn't even brush her kids' teeth every day and they've never gotten cavities."
If you've had trouble with your teeth, you need to take responsibility for your child's dental health -- just like you'd be vigilant if you've had a family history of high cholesterol or skin cancer. Unfortunately, antibiotics can't get rid of the cavity-causing bacteria in your child's mouth. That's why the American Academy of Pediatrics (AAP) actually urges pediatricians to ask parents about their own dental history by the time their baby is 6 months old, and to recommend taking extra precautions if a child is at high risk.