In the first quarter of the 20th century, American dentists drew attention to the fact that the teeth of residents of some states (for example, Arkansas) are covered with dark specks. As it turned out later, the mottling on the enamel was a consequence of the fact that in these areas the content of fluorides (fluoride compounds) in natural drinking water significantly exceeded the norm. However, the increased content of fluoride also had a positive effect - the incidence of caries among residents of these areas was on average lower than in the country.
Studies have shown that fluoride, when ingested in small quantities with water, is incorporated into dental tissue and makes it an unsuitable medium for bacteria to grow. A discussion arose: is it worthwhile to fluoride drinking water in order to prevent caries? Opponents of this idea won, and they decided to carry out caries prevention using small doses of fluorides in the form of tablets or additions to toothpaste.
In this case, the level of fluoride in toothpaste must meet the following condition: be high enough to have a pronounced preventive effect, and at the same time low enough so as not to cause the appearance of dark spots on the enamel of the teeth.