Worries about fluoride in water have evolved over the decades.One of the first water fluoridation studies was in Grand Rapids, Michigan in 1945.

Howard Pollick, fluoride spokesman for the American Dental Association, says the start date for the Grand Rapids trial was published in the newspaper, but then the study was temporarily postponed before health officials could notify local residents.

“All the phone calls came in, all the complaints came in that people were getting rashes, they were feeling bad all kinds of problems–they thought–because of the fluoride starting in the water. Well, in fact, it actually hadn’t started yet,” said Pollick, a professor at the University of California San Francisco School of Dentistry.

The study later showed dramatic improvements in the dental health of local school children. Many water systems across the country followed suit, adding fluoride to their drinking water to prevent tooth decay.

Fluoride helps repair a tooth that has started to decay. When bacteria in the mouth feed on sugars, they produce acids that can eat away tooth enamel and eventually cause a cavity. Teeth treated with fluoride are more resistant to acids.

In 1999, the Centers for Disease Control and Prevention listed water fluoridation among the top public health achievements of the 20th Century.

In recent decades, there are many more sources for fluoride protection, and the amount of fluoride that children are exposed to has increased.

Nearly every toothpaste on the drugstore shelf contains fluoride. So for that reason and others, this week the Public Health Service lowered its recommendation on the optimal fluoride level in water.

The government first suggested the lower fluoride level of .7 mg/L back in 2011, and in the interim many municipal water systems have already made the change.

Officials didn’t cite health problems; instead they explained a cosmetic issue. Too much fluoride can create a condition called fluorosis—white spots on the teeth.

Health officials continue to stress the benefits of water fluoridation. They say adding fluoride protection to community water has been a cost-effective dental health strategy.

“It’s more of social justice issue these days,” Pollick said.

“You didn’t have to pay for it, you didn’t have to go to the dentist, you could just go and drink the water,” says Joan Gluch, a public health dental hygienist, and interim division chief of community health at the University of Pennsylvania School of Dental Medicine. “It’s a great community benefit that cuts across access issues, still for a lot of folks in poverty.”

Pollick first became a dentist in 1967. That was the bad old days, he says, when he often had to remove three or four of his patients’ rotten teeth during one visit.

“The decay was rampant,” he said.

“My grandparents were fairly educated people, they didn’t have their teeth when they were 60 years old,” said Christopher Hughes, chief of the pediatric division at the Rutgers School of Dental Medicine.

“The improvement in dental health over the last century is phenomenal. And lot of that is attributable to fluoridation of community water supplies, it’s an undeniable fact,” Hughes said.

Still for many people, their most vivid impression of fluoride in water is that campy 1964 movie “Dr. Strangelove” where an insane brigadier general suggests that the USSR is polluting American water.

“Mandrake, have you ever seen a commie drink a glass of water? Vodka that’s what they drink, never water,” the movie general says. “Do you realize that fluoridation is the most monstrously conceived and dangerous communist plot that we’ve ever had to face?”

That’s the cultural baggage that dogs the fluoride debate, said Michael Connett, a volunteer attorney for the Fluoride Action Network.

That context makes it hard to communicate health concerns about the newer science on fluoride, he said.

“I think there’s a nebulous sense that this issue was resolved long time ago, the science settled 50 or 60 years ago, and the only people who oppose it are a bunch of crackpots,” Connett said. “And it’s really not the case.”

Recent studies have suggested that very high fluoride concentrations in water could hurt the thyroid or brain development in children. It’s too soon, Connett says, to assume that the lower fluoride levels used in American water won’t cause health problems.

Joan Gluch, from the University of Pennsylvania, said the “recent controversies” about cognitive impairment in children or hypothyroidism do not stand up to careful scrutiny.

“It is scary for parents to read the anti-fluoridation Web sites regarding potential lowered I.Q. in children in China, however, these studies were completed in areas in China with water fluoridation above 4.0 mg/L —much, much higher than we use in Philadelphia,” Gluch said.

The new water standard from the U.S. Public Health Service is the first update since 1962.

“I think it’s telling that it took so long for government health authorities to finally act on the obvious–that children are receiving far more fluoride than was intended, and I think the same will play out with the health concerns,” Connett said.

Pollick from the dental association says when you look beyond one or two studies—at the total evidence—there are no health problems linked to the low levels of fluoride used in drinking water in the United States.

But critics say over-the-counter topical products are a better way to protect people from tooth decay: Use fluoride directly on the teeth, and then spit it out.

“We now know that fluoride doesn’t need to be swallowed, and if there’s no need to swallow it, why are we adding it to the water where you have to swallow it?” Connett asks.