As the federal government adjusts its recommendations on fluoride levels in public water systems, Oregon is left wondering how to get fluoride in its largest communities.

Fluoride is hailed by dentists and public health as a low-cost and effective preventive measure against tooth decay. While in some places, fluoride exists naturally in the water, it is being added in others to reap the oral health benefits for the population. Studies have shown that fluoridation reduces tooth decay in children ages 4 to 17 by about 29 percent.

Nationally, 75 percent of Americans have access to fluoridated water. In Oregon, however, the figure is about 23 percent — among the worst in the country.

In fact, the Pew Charitable Trust reported in February that Oregon ranks in the bottom three among states that have the largest proportion of children lacking access to fluoridated water, at 82 percent. Portland is the largest city in the country without a fluoridated water system.

Portland voters rejected fluoride in a heated campaign a couple of years ago, and it’s unclear when the issue could be approached again, said Dr. Bruce Austin, Oregon Health Authority’s state dental director. But it could be another decade until another attempt could be realistically be made, he said.

“I don’t know,” Austin said. “I personally have a belief in what I’d like in Oregon. As far as how to enact that? That’s a tricky one. There are a lot of factors there, including being sensitive to people who have concerns about them.”

But the science is solid in the safety and effectiveness of fluoride, Austin said, despite some people’s opinion that adding fluoride in the water system is mass medication without consent or that fluoride causes bone cancers.

“There’s no verifiable science there’s any health or medical risk to fluoride when administered at the proper recommended levels,” Austin said.

The only two states that fall below Oregon in the Pew Charitable Trust’s rankings are New Jersey and Hawaii.

Salem, Keizer, Silverton, Turner, Sublimity, Dallas, Monmouth and Independence all have fluoride in their water systems. Eugene and Springfield do not.

Since 1962, the recommendation in fluoride addition to water systems was a range of 0.7 parts per million to 1.2 parts per million, because the assumption was that children drank different amounts of water depending on what climates they lived in.

Now, the U.S. Public Health Service says children drink the same amount of water across the country. In addition, there are now many other sources of fluoride, including toothpaste and mouthwash. The result is that some people are getting excessive amounts of fluoride, causing streaks or splotches on their teeth. The updated recommendation is now 0.7 parts per million.

Salem’s fluoride level was at 0.69 parts per million in a February 2014 sample check, according to Oregon Health Authority’s online drinking water data.

Austin emphasized that the dental fluorosis is barely visible and it’s only an aesthetic problem. The people who experience discoloring due to excessive fluoride do not face health risks, he said. In addition, Austin said, fluoride levels are easily controllable, so local water districts can target a specific amount and hit it easily. That further diminished the need to provide a range to follow.

Water fluoridation is in the state’s Strategic Plan for Oral Health, which sets goals for oral health for 2020. Oregon hopes to meet the bar of 25 percent of the population having accessing to fluoridated water. The national Healthy People 2020 objective is 79.6 percent.