TUESDAY, Sept. 2 (HealthDayNews) -- In a bit of bad news for children with a sweet tooth, a new study suggests soft drinks and powdered beverages cause more cavities than fruit juice, but even OJ can spell trouble if kids overdo it.

The research "drives the stake into the heart" of any doubt that sugary drinks contribute to tooth decay, says Dr. Matthew Messina, a dentist and spokesman for the American Dental Association. "Finally, we've got the hard science that backs up what we've believed for a long time."

In these days of fluoridated water and fancy toothbrushes, cavities remain a major health problem among children. "Too often parents have thought, 'It's just a cavity or two.' It's a disease, a disease process that's preventable," Messina says.

Sugar remains a prime villain in the eyes of dentists, although researchers disagree over how much of a role it plays in cavities.

When sugar reaches the teeth, it interacts with bacteria and begins to ferment. "You produce acid as a byproduct, kind of like making wine," explains study co-author Teresa A. Marshall, a clinical assistant professor of preventive and community dentistry at the University of Iowa.

The acid, in turn, erodes the enamel of teeth. The body tries to heal the erosion by repairing the damage, but failure results in cavities that require fillings.

In the new study, researchers examined the findings of an ongoing analysis of the dental health and daily diets of a group of children. The 642 kids were aged 4 to 6 at the beginning of the project, and are now around 10 and 11.

Marshall and her colleagues report their findings in the September issue of Pediatrics.

The children with more cavities reported drinking more soft drinks and powdered beverages, such as Kool-Aid, lemonade and power drinks.

Kids who drank a lot of fruit juice had more cavities, too, "but it was really a much lower effect than we saw with the other two beverages," Marshall says. "This doesn't mean that excessive drinking of juice is perfectly safe. But it isn't as bad as the others."

The researchers didn't notice any unusual cavity problems among children who drank a lot of juice drinks that were not 100 percent juice.

It's not clear why fruit juices are better for the teeth than the other beverages, considering that they all come loaded with sugar, she says, adding "If you talk to any pediatric dentist who sees kids who are slugging down juice 24-7, they're going to have rotten teeth."

One theory is that kids may expose their teeth to less sugar when they drink fruit juice because they may finish the beverages quickly and not sip them over long periods of time, Marshall says. It's also possible that children who drink fruit juice may have other habits that protect their teeth from decay, she adds.

While the study suggests that children may safely drink fruit juice and not put their teeth at risk, parents should remember that experts think young kids should only drink 4 to 6 ounces of juice a day, Marshall said. That's less than a large glassful.

"Keep an eye on what your children are drinking," Messina advises, especially considering the many soft drinks and power drinks that are available at school cafeterias.

And what about milk, which has sugars of its own? The researchers found no link between higher consumption and more cavities.

More information

Learn more about kids and tooth decay from the University of Maryland or the Academy of General Dentistry.