Despite what dentists keep telling us about the protective effects of fluoride on people's teeth, virulent myths insisting otherwise somehow manage to persist.

These kinds of mistaken beliefs might be false, but their consequences are very real. Like when, in 2007, the people of Juneau, the capital of Alaska, voted to stop putting fluoride in their drinking water, over concerns about what harms it might be doing to them.

The decision, coming after years of debate in Juneau between dentists and other groups, resulted in a massive, immediate change in public health policy for the city and borough's residents.

But while research into the benefits of water fluoridation has existed for decades – and suggests fluoride reduces cavities (aka caries) and associated dental disease – less is known about the effects of fluoride cessation.

In other words, what happens when a population suddenly stops taking fluoride in their drinking water, like Juneau's citizenry did?

Now, thanks to a new study led by first author and public health researcher Jennifer Meyer from the University of Alaska Anchorage, we've got new insights into the subsequent effects.

In the study, Meyer assessed Medicaid dental claim billing records for two groups of children and adolescents aged 18 or under.

One of these groups represented what the researchers call "optimal" community water fluoridation (CWF) exposure: 853 non-adult patients on behalf of whom Medicaid dental claims were filed in 2003, years before the fluoride cessation began in 2007.

The other group was made up of 1,052 non-adult patients from families who similarly met Medicaid income requirements, and who made the same kind of dental claims almost a decade later, in 2012.

Of course, that's five years after the fluoride was taken out of Juneau's tap water, so that group represents what the researchers describe as "suboptimal CWF conditions".

That time gap resulted in a statistically significant difference in children's cavity levels, the researchers say.

"By taking the fluoride out of the water supply… the trade-off for that is children are going to experience one additional caries procedure per year, at a ballpark (cost) of US$300 more per child," Meyer explained to KTOO News.

Those figures are based on the youngest children assessed in the study, aged under six years of age.

Among those patients, kids who were exposed to fluoride in their tap water had on average 1.55 caries procedures annually – but this jumped to 2.52 procedures annually for the children in the suboptimal group.

The effect was more subtle for age groups older than the 0 to <6 age group, but nonetheless, every age group analysed in the study (0 to <6, 0 to <7, 7 to < 13, 13 to 18, and 0 to 18) experienced higher levels of cavity procedures if they didn't have fluoride in their drinking water.

It's not known for sure why the cessation demonstrated less of an effect on older children, but the researchers suggest the older kids in the suboptimal cohort may have received a partial protective effect from any fluoride exposure when they were younger (ie. before 2007, when the fluoride ban kicked in).

"Previous research indicates that without the presence of optimal levels of fluoride in drinking water, and thus in the mouth and saliva, teeth may form with weaker enamel and lack the ability to remineralise early signs of decay," the authors explain in their paper.

"We expected to observe more significant impacts among patients with the lowest exposure to optimal CWF."

Of course, more cavities necessitating dental procedures means more money is needed to fix the damaged teeth.

After adjusting for inflation, those increased costs represented anywhere between a 28 percent to a 111 percent jump for the various age groups, with the maximum increase being just over $300 annually for children in the 0 to < 6 age group who grew up with suboptimal CWF exposure.

Basically, according to the researchers, the cessation was a very expensive move.

"The cost to have a fluoride management program, to actually fluoridate the water, is pennies by comparison to what it costs to treat a cavity," Meyer told KTOO, pointing out that voluntary alternatives like pharmacy fluoride tablets can also prevent decay, but come with their own problems.

"I think that's a great option for people, but it's also a headache. You gotta get the prescriptions filled, you gotta remember to give it, you've gotta make sure kids don't take more than one – you know, there's risks to that… It sets up a precedent for inequity."

It's unknown whether the latest findings will be enough to sway the minds of other local city assemblies considering enacting their own fluoride bans – but for those who do the actual science, the science on fluoride remains perfectly clear.

"These results support current evidence that even in modern conditions with widely available fluoride toothpaste, rinses, and professionally applied prophylaxis, CWF is associated with population benefits," the authors write, "including cost effectiveness and caries prevention."

The findings are reported in BMC Oral Health.