Fluoride has transformed modern dental care by dramatically reducing the number of cavities in children’s teeth.

But now there is a growing concern that some children are getting too much of a good thing.

While dentists are seeing less tooth decay, they are seeing more cases of dental fluorosis – a discoloration of the teeth’s enamel, caused by ingesting too much fluoride during early childhood, when permanent teeth are developing.

The excess exposure is not simply because of the fluoride that has long been added to many public water systems, dentists say, but because children are now getting fluoride from many things: toothpaste, cavity-fighting mouth rinses, fluoride drops and tablets, and even sodas, juice drinks and other processed foods that can contain fluoride if they are manufactured with fluoridated water.

“The general thought is we have many more sources of fluoride than we did 30 to 50 years ago,” said Robert Selwitz, a dentist and researcher at the National Institute of Dental and Craniofacial Research.

The most recent data, based on a 1986-87 national health survey, found that 22 percent of children had fluorosis.

In milder cases, the teeth’s enamel has lacy, chalk-like markings, or larger, opaque white spots. In more severe cases, there can be areas of brown stain; in extreme instances, enamel is pitted and brittle.

Dental fluorosis is considered a cosmetic issue, not a health concern, and there is no evidence to suggest that fluoride is causing problems in other parts of the body, experts say.

Still, the increased prevalence is causing a rethinking of how to provide fluoride protection without overdoing it.

Public health officials remain committed to the fluoridation of public water systems, which began in some communities in the United States in 1945. Officials say tooth decay is a much worse and more costly problem than spotted teeth. About two-thirds of Americans who are served by public water systems get fluoridated water.

How much is too much? Experts suggest infants under 6 months old should not ingest more than 0.7 mg a day; 6 to 12 months should not get more than 0.9 mg a day, and children 1 to 3 years should not get more than 1.3 mg a day. (An 8-ounce glass of fluoridated water contains about 0.25 mg.)

New recommendations from the federal Centers for Disease Control and Prevention (CDC) call for a more judicious use by young children of other fluoride sources, including supplements and toothpaste. Dental fluorosis occurs before permanent teeth erupt, with the ages of 15 to 30 months thought to be especially critical. After about the age of 6, when the teeth come in, the damage from excess fluoride has already been done.

Scott Presson, a dentist in the CDC’s Division of Oral Health, said the goal is to “reinforce the positive benefits of fluoride, yet make the point that there are some minor changes that people need to be aware of,” to prevent fluorosis.

It’s a tricky public health message to convey because people have been well schooled in the positive role of fluoride in preventing cavities. Also, opponents of water fluoridation are vocal and eager to pursue any negative possibilities. They already say fluoridated water increases the chances for ailments such as cancer, osteoporosis, bone fractures, and Alzheimer’s disease – claims the CDC says are unfounded – and the rise in fluorosis adds to their anti-fluoride stand.

“It’s a red flag,” said Paul Connett, of Fluoride Action Network, an anti-fluoride coalition. “Fluorosis is saying ‘this kid has been overexposed to fluoride.’ ”

“It tells us something else might be going on,” said Connett, a chemistry professor at St. Lawrence University in New York.

The new CDC recommendations, issued in August, say doctors and dentists should not automatically prescribe fluoride drops or tablets to babies and young children simply because the family’s water supply is non-fluoridated. Rather, health professionals are advised to prescribe supplements only after consideration of all of the child’s potential sources of fluoride and whether the child is at risk for cavities.

The CDC’s recommendations also urge greater restraint in the use of fluoride toothpaste by young children because it is thought to be a major source of fluoride ingestion. The agency advised parents to monitor the amount of toothpaste their children use, limiting it to the size of a pea. Children younger than 2 should not use fluoride toothpaste at all except on a doctor’s or dentist’s advice.

“If you put a big ribbon of toothpaste on a kid’s brush, they are going to ingest a big portion of it,” said Mark Helpin, head of pediatric dentistry at the University of Pennsylvania’s School of Dental Medicine.

Steven Levy, a dentist and researcher at the University of Iowa who has done studies measuring fluoride intake, found that children were more apt to use more toothpaste when it was a kid-pleasing flavor.

The CDC offered this example: A child-sized toothbrush will hold 0.75 to 1 gram of toothpaste and each gram contains 1 milligram of fluoride. Given that a child under the age of 6 will swallow on average 0.3 gram of toothpaste per brushing, and even as much as 0.8 gram, “multiple brushings with fluoride toothpaste each day can result in ingestion of excess fluoride,” the CDC said.

Children’s toothpastes in the United States contain the same fluoride concentration as adult brands; in some other countries, reduced-fluoride toothpastes are available. The CDC’s recommendations urge manufacturers to produce lower-fluoride products, but Levy, who helped draw up the recommendations, said that would be difficult for companies to do because the FDA would still require proof that the toothpastes are good at fighting cavities.

Part of the problem in devising a strategy for preventing fluorosis is that it’s hard to know how much fluoride children are taking in. Children are exposed to different sources of water – at home, day care centers, schools. Even water companies that add fluoride for some communities may not do so for all customers. An 8-ounce glass of fluoridated water typically contains 0.25 milligram of fluoride, Levy said. So does an 8-ounce glass of soda, if the soda is made with fluoridated water.

Levy did studies measuring total fluoride intake in groups of children, ranging from infancy to age 6, and found that at various ages, anywhere from 10 percent to 25 percent of the children had levels of fluoride that exceeded the recommended amount for their weight – putting them at risk for fluorosis.

Donna Polin, of Dresher, Montgomery County, said she was surprised when her daughter Molly’s front teeth came in marked with white spots.

“I wasn’t thrilled,” she said. “I didn’t know why it happened.”

The family lives in an area with non-fluoridated water, so Polin had dutifully given Molly, now 8, first fluoride drops and then tablets. She is now cutting back on the fluoride supplements she gives her younger daughter, Jennifer, who is 5, in hopes of preventing her teeth from developing fluorosis.

Already some steps have been taken to reduce the chances of young children getting too much fluoride: infant formulas contain less fluoride than they used to; the recommended doses for supplements have been cut back, and toothpaste packages now contain warnings about young children using too much.

Parents are also more aware of the issue, said Michael Rosenbaum, a Fort Washington dentist who runs the dental residency program at Temple University Children’s Medical Center.

“I have parents come in with fluorosis on their teeth and they want to know how to prevent it with their children,” he said.