Decades after most of the rest of the nation accepted adding fluoride to the water supply to prevent tooth decay, the issue remains a flashpoint in Oregon.

“Of all the issues in the state, this is one of the most contentious,” says Brett Hamilton, a director of the Oregon Dental Association, which supports fluoridation. “It’s frustrating for us.”

Two-thirds of the U.S. population, or nearly 200 million Americans, drinks from fluoridated water supplies. Proponents cite the 60-year history of fluoridation and its track record of safety. The federal Centers for Disease Control and Prevention calls fluoridation one of the 10 most important public health advances of the 20th century, and it estimates that every dollar invested in fluoridation saves $38 in dental costs.

But in Oregon, an unlikely coalition — anti-government conservatives, advocates of local control, and environmentalists — has blocked statewide fluoridation. Oregon ranks 48th, trailed by Hawaii and New Jersey, in percentage of residents with fluoridated water.

Fluoridation has driven a wedge between environmental groups and public health advocates, says Kurt Ferre, a Kaiser Permanente dentist who backs fluoridation. “We’ve got a major fight going on here.”

Bills to bring fluoridation to Oregon cities with at least 10,000 residents have come up — and stalled — in the past three legislative sessions. This session, Sen. Bill Morrisette, D-Springfield, introduced Senate Bill 33, which echoes the previous bills. But the bill has stalled in the Senate Health and Human Services Committee, chaired by Morrisette, with no hearing scheduled.

Morrisette says no other committee member supports approving the bill for a floor vote. While some proponents believe the House and Senate would pass the bill if it ever reached the floor, he says it’s tough to get such a bill out of committee.

“You immediately draw a roomful of people, some who think it is poison and others who think it is the best thing that can happen to people.” Morrisette says. “I’m in the middle ground.”

Opponents, including a vocal minority of doctors and dentists, raise a variety of concerns. Some say the mainstream pro-fluoridation consensus in the dental profession is based more on conventional wisdom than on hard science. Others say mass fluoridation unfairly trumps individual choice. Still others argue against fluoridation on environmental grounds, saying the health benefits are not sufficient to justify adding a chemical to clean water.

Almost every major environmental group in Oregon, including the Sierra Club’s state chapter, opposes fluoridation, says Brent Foster, executive director of Columbia Riverkeeper.

“In Oregon, we are blessed with some of the best drinking water in the country,” says Kimberly Kaminski, executive director of Oregon Citizens for Safe Drinking Water. “To intentionally add ‘toxic waste’ to our drinking water seems really ludicrous.”

Critics also cite a 2006 National Research Council report that raised questions about high doses of fluoride and a recent advisory by the American Dental Association to limit use of fluoridated water in mixing baby formula.

Under the Safe Drinking Water Act, the Environmental Protection Agency sets standards for chemicals in public water supplies. The maximum standard for fluoride — a mineral found naturally in tiny amounts in all water — is 4 parts per million, four times as high as in artificial fluoridation.

The EPA asked the research council, which advises the federal government on scientific questions, to evaluate the evidence for the fluoride standard. The result was a 530-page report issued in March.

The report did not weigh in on health risks or benefits of artificially fluoridated water. But it concluded that the EPA standard for fluoride in drinking water should be tightened below 4 parts per million.

The research council cites two main concerns about high levels of fluoride in water. First, it can cause a condition called fluorosis, a white spotting of the tooth surface that dentists regard as a cosmetic issue rather than a health risk. Second, there is conflicting evidence about whether high fluoride levels may contribute to hip fractures.

Gordon Empey, a dental consultant to Oregon’s public health division, said fluorosis poses no health threat. And no fluoridated water supply contains levels of fluoride as high as the standard the research council considered. He says fluoridation reduces dental cavities by 18 percent to 40 percent and benefits low-income people least likely to have access to good dental care.

Sen. Alan Bates, D-Ashland, an osteopathic physician, says he has seen no studies that prove fluoride to be safe or unsafe. Nor is it clear, he adds, that ingested fluoride prevents cavities, though direct application certainly does.

“A better option,” he says, “is to reform health care, and part of that reform is better dental care for everyone in Oregon.”

At the request of the British Department of Health in 2000, the Evidence-based Practice Center at Oregon Health & Science University reviewed 214 published studies on the safety and effectiveness of fluoride in drinking water. OHSU researchers found clear evidence that fluoride prevents dental decay. They found an increase in fluorosis, but the study found “no clear evidence of other potential adverse effects.”

Fluoride opponents have long had to live down a reputation as “kooks,” says Kaminski of Oregon Citizens for Safe Drinking Water. But she says new findings about fluoride add to concern about its potential health effects and skepticism about its benefits, she says. “It’s getting more and more difficult to portray that view as fringe.”

While it did not conclude that fluoridation is unsafe, last year’s research council report “kind of reads like an anti-fluoridation manifesto,” says Foster of Columbia Riverkeeper. He also calls the dental association’s advisory against using fluoridated water in mixing infant formula troubling.

The CDC takes a more measured position.

“Recent evidence suggests,” the agency says, “that mixing powdered or liquid infant formula concentrate with fluoridated water on a regular basis may increase the chance of a child developing the faint white markings of very mild or mild enamel fluorosis. Typically, very mild or mild fluorosis is barely noticeable, if noticed at all.”

Senate Republican leader Ted Ferrioli, of John Day, says most of his constituents get their water from wells or from small community water supplies unaffected by the proposed fluoride bill. Still, he says he opposes the bill largely on a philosophical basis.

Ferrioli says children can get fluoride in toothpaste and mouthwash. Putting chemicals in the water supply gives people no choice and sets a bad precedent, he says.

“If I can fluoridate your water, where do I draw the line?”