SATURDAY, March 25 (HealthDay News) -- Add cavities to the growing list of health problems plaguing American kids.

More than 25 percent of preschoolers suffer from tooth decay, a recent federal study found.

"National studies are showing that early decay is on the increase, and that's shocking, actually," said Dr. Mary Hayes, a Chicago dentist and a spokeswoman for the American Dental Association. "It's really a silent epidemic."

The U.S. Centers for Disease Control and Prevention study found that more than 4 million preschoolers are affected by tooth decay, a leap of more than 600,000 children in a decade.

Dental professionals suspect the problem is being spurred by the increased consumption of sugary drinks and snacks, as well as lax tooth cleaning.

"The science now is, we aren't worried about teeth being hard or soft," Hayes said. "The issue more is the bacteria living in your mouth, and how happy they are there."

Plaque, a sticky film of bacteria, constantly forms on teeth from foods containing sugars or starches, according to the American Dental Association. The bacteria in plaque produce acids that attack tooth enamel, and the stickiness of the plaque keeps these acids in contact with your teeth. As the enamel breaks down, a cavity forms.

Parents need to realize that even though baby teeth are destined to be replaced by permanent teeth, they still need to be cared for, Hayes said.

For starters, a decayed baby tooth can cause pain and suffering for years if left untreated.

"Baby teeth are with us longer than people think," Hayes said. "People think if a baby tooth gets decay, that's OK because the tooth is disposable. But the last ones don't leave until kids are about 12."

Tooth decay in baby teeth also tends to predict future tooth decay and orthodontal problems in permanent teeth, according to the American Dental Association.

Care for a child's teeth should start before the first tooth is even in the mouth, experts say. Parents can get infants used to having their teeth cleaned by running a wet washcloth around their mouth before the first tooth erupts.

Once the first tooth emerges, parents must be ready to kick-start dental-health habits that can help their children for a lifetime, said Dr. Kimberly Harms, a dentist in Farmington, Minn.

"Most people don't understand they have to start cleaning those teeth the minute they erupt into the mouth," Harms said. "Bacteria can form on that tooth, plaque can form on that tooth, as soon as that tooth erupts."

Parents can use a gauze pad to clean toddlers' teeth, or rubber brushes that fit over their fingertips. They also should clean and massage gums in areas that remain toothless.

Early tooth decay also can be avoided by never allowing a child to fall asleep with a bottle containing milk, formula, fruit juice or sweetened liquids, according to the American Dental Association. Generally speaking, parents should avoid filling a child's bottle with sweet liquids such as sugar water or soft drinks.

"It's not the amount of sugar a child eats that causes the problem, but the number of exposures," Harms said. "Every time you expose your mouth to that, you get that bacteria active. Children sipping or drinking any drink other than water, every time they sip, it increases the amount of bacteria."

Parents should plan on taking their child to the dentist by the first birthday, to check for early signs of decay, Harms said.

And once all the baby teeth have grown in, flossing should be added to the regular dental health regimen. Harms said new devices like floss-on-a-stick have made flossing a little easier for parents.

"That has made a huge difference in getting kids to floss, because they love getting back in there with that little device," she said.

Once a child is 2 years old, parents can begin using a pea-sized amount of toothpaste on a toothbrush for cleaning. At that age, kids are able to spit out the toothpaste and not swallow it.

However, experts advise parents to continue brushing their child's teeth up to at least age 6 or 7, before handing over the task to the child.

"Most kids under 6 don't have the fine motor skills to brush their teeth," Hayes said. "The brush is in their mouth, but they aren't cleaning anything."

More information

To learn more about kids and dental care, visit the National Library of Medicine.