Gov. Ron DeSantis of Florida signed a bill into law on Thursday that bans the addition of fluoride to public water supplies, making Florida the second state to prohibit the widespread public health practice.

Studies show a clear correlation between fluoridated drinking water and improved oral health, including fewer dental cavities. Fluoride was added to a city’s water supply for the first time in 1945, and the practice spread around the country in the following decades.

But Mr. DeSantis and other prominent Republicans have criticized fluoridation as an example of government overreach, drawing parallels to masking and vaccine mandates during the coronavirus pandemic.

How It Fits Into the National Landscape

The law puts Mr. DeSantis and the Republicans who dominate the Florida Legislature at the front of a growing national movement. Robert F. Kennedy Jr., President Trump’s health secretary, recently called for all states to ban fluoride in drinking water. In March, Utah became the first state to outlaw the practice.

A handful of other states, including Ohio and Texas, and a number of local governments are weighing fluoride bans.

In 2022, the most recent year for which C.D.C. data is available, about 63 percent of Americans lived in areas with fluoridated drinking water.

The Argument In Favor of a Ban

Fluoride is naturally present in many foods, and experts say that excessive exposure to fluoride over a long period can lead to health problems. Federal safety guidelines for how much fluoride to add to water supplies have been lowered in recent years to reduce any risk, including after a recent court order.

With trust in public health eroding from the coronavirus pandemic, a movement to eliminate fluoride from drinking water has gained significant steam.

Opponents of fluoridation have cast their concerns as a matter of protecting bodily autonomy, and have cited the possibility of cognitive effects on children and infants from excessive exposure. Powerful people like Mr. Kennedy and other top Republicans have publicly questioned fluoridation’s safety.

Robert F. Kennedy Jr., the secretary of health and human services, recently called for all states to ban fluoride in drinking water.Credit…Haiyun Jiang for The New York Times

“It’s forced medication, when they’re jamming fluoride into your water supply,” Mr. DeSantis said at a news conference last week, standing behind a placard that hailed “the free state of Florida.” Referring to the oral health benefits of fluoride, he said, “I’m not saying that’s not true, but we have other ways where people can get access to fluoride.”

“We should all agree that we want people to have informed consent when it comes to these things,” he added.