Fluoride is the ionic form of fluorine, and is instrumental in protecting bone and tooth enamel from loss of constituent minerals. Fluoride is most concentrated within tissues such as cementum, bone, dentin, and enamel. Fluoride is proposed to enhance the precipitation of hydroxyapatite crystals in solutions of calcium and phosphate and therefore tends to prevent the demineralization of bone and teeth. It has been further proposed that fluoride becomes integrated within the hydroxyapatite crystals, creating enlarge and less soluble crystals. As these crystals are less soluble and less reactive, dissolution of the tooth structure by acidic by-products of microorganism metabolism cannot occur as readily. Bone is also less likely to demineralize due to the decreased solubility of the fluoride containing crystals.