Fluoride occurs naturally in rocks and soil and is among the most abundant substances in the earth;s crust. As a result, it’s often found in a dissolved form in lakes, rivers and groundwater. Because fluoride is so common, and because human activities such as manufacturing release it into the air, all vegetation and almost all foods contain traces of it.
As early as the 1930s, scientists noticed that people who drank naturally fluoridated water had less tooth decay than people who didn’t. They soon realized that fluoride might be nature’s answer to tooth decay, and more research in the 1940s and 1950s showed that it could contribute greatly to dental health.
As a result, many communities in Canada and the United States began to add fluoride to their drinking water. Manufacturers of dental care products also started putting it into toothpastes, rinses, gels and varnishes. Dietary supplements like fluoride lozenges also became available. With these products, fluoride is available to everyone, even when their water doesn’t contain it.