Hydroxylapatite

Hydroxylapatite is a naturally occurring mineral form of calcium apatite, mainly composed of calcium (Ca), phosphorus (P), and oxygen (O), with the formula Ca5(PO4)3(OH). It is the hydroxyl endmember of the complex apatite group. The OH- ion can be replaced by fluoride, chloride or carbonate, producing fluorapatite or chlorapatite. It is usually white in color and appears in the crystalline form.

Structure and Composition

Hydroxylapatite has a hexagonal crystal structure. Each unit cell is composed of three columns of Ca2+ cations, with a column of PO4^3- anions in the middle, and hydroxyl groups at the ends. The high charge of the PO4^3- anions leads to a strong covalent character in the bonding within the crystal structure, which gives hydroxylapatite its high strength and hardness.

Occurrence

Hydroxylapatite is the main component of tooth enamel and bone mineral. A relatively rare form of hydroxylapatite is found in the teeth and bones of vertebrate animals. This form of hydroxylapatite has been extensively studied in the field of biochemistry due to its role in the formation of bones and teeth.

Uses

Hydroxylapatite has a wide range of applications in the field of medicine and dentistry. It is used in orthopedic surgery for bone repair and as a coating on orthopedic implants. In dentistry, it is used as a filler in dental composites and as a toothpaste additive to help remineralize enamel and prevent tooth decay.

See Also

• Apatite
• Calcium phosphate
• Tooth enamel
• Bone mineral