Fluoride has long been considered an easy, essential way to prevent dental decay. It’s the result of adding an extra electron to fluorine, one of the most abundant elements on the planet. Discovery News (DN) reported fluorine is found in sea water, fish, tea, and a naturally occurring substance in minerals, which is to say, rocks. And during rock erosion, fluorine is washed into the water supply.

Following the 1940s, when “people living near natural water sources with one part per million fluoride had fewer cavities,” fluoride became a staple in toothpaste, food, and water, to prevent cavities, fillings, and otherwise tooth pain and suffering for those further away from these natural sources. The effects of this have been heavily debated, from whether or not fluoride is toxic to whether or not it's capable of causing a mental disorder.

Yet, water-born fluoride and topical fluoride, like toothpaste, aren't interchangeable. DN cited a study that found people living on the coast had fewer cavities after consuming fluoride-rich fish, whereas a separate study found kids drinking sodium fluoride (water) also had fewer cavities — possibly from the water, possibly not.

DN added municipal drinking water sources get fluoride as an “odorless, tasteless by-product of phosphate fertilizer making,” a source the World Health Organization says poses no perceptible changes to water. In fact, WHO found adding fluoride to water is the most effective public health measure against tooth decay.