Simply put: Fluoride forms a kind of protective film around your teeth and protects them from caries. To better grasp fluoride, it helps to understand how tooth decay occurs in the first place:Our teeth are made up of enamel, dentin and dental cement. Enamel is the hardest substance in the human body and is composed mainly of calcium and phosphate. Our teeth are surrounded by a biofilm (plaque) that contains numerous microorganisms. These bacteria break down carbohydrates from food into acids. The acids can damage the tooth because they dissolve calcium and phosphate from the enamel, thus softening it. Fluoride counteracts this. It improves the remineralization of the teeth by helping to reincorporate the minerals into the tooth lattice. It also builds up the enamel and makes it more resistant to acids. As a result, the tooth enamel regains an intact surface.