Dr. Thomas Sorensen talks to Brenda Martinez about fluoride supplements for her daughters Sofia, 3, left, and Alessandra, 2. Photo by K.M. Cannon.

Dr. Thomas Sorensen sat in his office and told Brenda Martinez it was easier to talk to her about the need for decay-preventing fluoride for her daughters because she lived in Pahrump rather than Las Vegas or Henderson.

The remark so surprised her that she momentarily stopped trying to keep her two young daughters from scampering around a dental chair.

"How come?" she asked.

"There's no fluoride in the drinking water in Pahrump and Nye County like there is in Vegas and Clark County," the dentist explained. "So I know it's best that your children take fluoride supplements to help prevent cavities. In Las Vegas and Clark County, there is fluoride in the drinking water, but so many families are now drinking bottled water without fluoride, it's much harder to figure out a child's needs."

That short exchange, which played out in the offices of A Children's Dentist, 6169 S. Rainbow Blvd., indicates the quandary dental professionals and parents find themselves in as people turn increasingly to nonfluoridated bottled water for drinking.

Many dentists say the move to bottled water, along with home water treatment systems that remove fluoride and other minerals from water supplies, is at least partially behind a comeback in cavities among children today.

Sorensen says when making recommendations to patients, he has to try and pin down how much fluoridated tap water a child is drinking at home or at school.

"I'm always going to err on the side of caution, because too much fluoride can hurt a child's teeth," he said last week from his office north of Interstate 215.

The federal Centers for Disease Control and Prevention ranks the fluoridation of public water supplies as one of the top 10 public health achievements of the 20th century. And the American Dental Association cites studies showing that water fluoridation reduces dental decay by 15 to 40 percent.

But in Clark County, which didn't add fluoride to the public water supply until 2000, dentists say they are seeing more children with cavities than they did just a few years ago.

There is no doubt, Sorensen said, that the usual culprits -- soft drinks, junk food and lack of parental supervision of diet -- continue to play a large role in the declining dental health of children.

But, he said, "In general, the decay rate among children is increasing. And the trend to bottled water has something to do with it.

"What makes this increase in tooth decay of children different is that we're seeing people who believe they're being health conscious by buying bottled water."

According to the American Dental Association, fluoride builds strong, decay-resistant enamel. Children 6 months to 16 years old need fluoride; by the age of 16, enamel formation is completed.

It's recommended that preschoolers drink at least one pint of fluoridated water each day. By the time the child is old enough to attend school, the recommendation is for a quart.

In municipalities that don't fluoridate the water supply, dentists recommend children get prescription fluoride supplements.

Dr. Christine Navales, a practitioner with On-Site Dental in Las Vegas, said dentists now are asking parents about their children's bottled water intake as part of exams.

"There is an increase in cavities in children, but I don't know if we can single out bottled water."

Indeed, only anecdotal evidence supports the concerns of Sorensen and other dentists that too much bottled water is leading to an increase in cavities.

"We've got to educate parents and caregivers earlier on," said Dr. Wendy Woodall of the University of Nevada, Las Vegas' School of Dental Medicine.

"Fluoride is definitely part of the equation in individualized treatment programs we need to make for more children as the oral decay problem worsens."

Stephen Kay, vice president of communications for the International Bottled Water Association in Alexandria, Va., disputes the notion that bottled water is hurting children.

"There are no scientific studies to support a correlation between the drinking of bottled water and cavities in children," he said.

The American Dental Association, however, takes this stand: "If bottled water is your main source of drinking water, you could be missing the decay-preventive benefits of fluoride."

Bottled water consumption continues to rise.

In 2001, Americans purchased 5.1 million gallons. In 2005, that jumped to more than 7.5 million gallons. It is the second-largest commercial beverage category by volume in the United States, trailing only the soft drink market.

Only 20 of the nation's 160 bottled water companies add fluoride to their product.

Jim Price, a spokesman for Ozarka Water in Oklahoma City, said sales of bottled fluoridated water are rising. The reason is "because of people listening to their dentists."

Of the company's six lines of bottled water, one contains fluoride. Ozarka soon will bring to market a one-gallon jug of fluoridated water, Price said.

Kay said his association does not carry statistics on the amount of fluoridated water sold. He said the association recognizes that fluoride is valuable to oral and dental health. But he noted that people are able to get fluoride through other foods and liquids.

Low levels of fluoride occur naturally in Southern Nevada's water supply. The Southern Nevada Water Authority adds fluoride to those low levels to bring the level within the range recommended by the U.S. Public Health Service. Temporary topical fluoride also comes from toothpastes and gels.

According to the American Dental Association, a recent study found a 29 percent reduction in tooth decay among children and adolescents who drank fluoridated water. Without fluoridation, "there would likely be many more than the estimated 51 million school hours lost per year in this country because of dental-related illness."

Las Vegas Valley Water District customers pay an average of about 4 cents per month to cover annual fluoridation costs, which total about $350,000, according to the Southern Nevada Water Authority.

Though fluoridation of public water supplies is supported by a long list of groups including the National Academy of Sciences and the American Medical Association, some still find it dangerous.

Jeff Green, the national director of the Citizens for Safe Drinking Water advocacy group, based in San Diego, said Americans are getting too much fluoride. One concern in that regard is fluorosis, which creates white spots or mottling on the teeth.

Anti-fluoridation groups have also said kidney and cardiovascular problems can be exacerbated by fluoridated water.

But Reno dentist Arnold Pitts, president of the Nevada State Dental Association, said he wishes the entire state was using fluoridated water.

"It's particularly necessary where our children are underserved" by dentists, he said. "There is rampant decay in children, and it ends up causing this state an inordinate amount of money."

Still, Sorensen said, it is critical that dentists be cautious on providing fluoride supplements.

"The taking of the history of our patients is more important than ever. The last thing we want to do as dentists is create a problem when we are trying to do good."