Hydroxyapatite in tooth enamel (HA)

Hydroxyapatite in tooth enamel is a crystalline calcium phosphate mineral, with the chemical formula Ca₁₀(PO₄)₆(OH)₂, comprising approximately 95–98% of mature enamel by weight. This dense, highly organized mineral arrangement gives enamel its exceptional hardness and durability, making enamel the hardest substance in the human body. While pure hydroxyapatite is the core mineral, "biological hydroxyapatite" in enamel is carbonated and includes trace elements such as fluoride, magnesium, and strontium, which alter its physical and chemical properties. Enamel hydroxyapatite forms microscopic rods (prisms) extending from the dentinoenamel junction to the tooth surface, interwoven in a complex pattern that enhances resistance to fracture and wear. Hydroxyapatite itself is not a molecular drug target, receptor, or protein, but it is central to dental pathology (caries, erosion, fluorosis) and the mechanism of protective and remineralizing dental therapies.

Other names

HydroxylapatiteBiological hydroxyapatiteEnamel hydroxyapatiteTooth enamel mineral

Topical fluoride converts hydroxyapatite to fluoroapatite, which is more acid-resistant Remineralization agents provide additional calcium and phosphate ions to repair demineralized hydroxyapatite Physical coatings (varnishes/pastes) deposit synthetic hydroxyapatite into eroded or demineralized areas