Hydroxyapatite and Fluorapatite (HAP/FAP)

Enamel hydroxyapatite is the primary inorganic constituent of human tooth enamel, providing the structural hardness necessary for mastication and protection of internal dental tissues (StatPearls, 2023). It consists of a crystalline calcium phosphate lattice that is susceptible to demineralization in acidic environments created by cariogenic oral bacteria (NIH, 2021). When fluoride is introduced, it interacts with this mineral to form fluorapatite or fluoridated hydroxyapatite through an ion-substitution mechanism where fluoride replaces hydroxyl ions (PubChem, CID 14781). Fluorapatite is more chemically stable and resistant to acid dissolution than pure hydroxyapatite, making it a central target for caries prevention and remineralization therapies (Wikipedia, 2024). However, excessive fluoride exposure during the developmental stages of enamel can lead to dental fluorosis, a condition where the mineral structure becomes porous and hypomineralized (PubMed, 2022). Therapeutic agents like sodium fluoride and silver diamine fluoride are specifically designed to modify this mineral substrate to enhance its durability and arrest decay.

Other names

Enamel mineralCalcium hydroxyapatiteFluoridated hydroxyapatiteFluorapatiteCa10(PO4)6(OH)2Ca10(PO4)6F2

Fluoride ions substitute hydroxyl groups in the hydroxyapatite crystal lattice to form fluorapatite, which has a lower solubility product and higher resistance to acid-induced demineralization (remineralization).