Hydroxyapatite is a calcium phosphate mineral with the formula Ca5(PO4)3(OH), often written as Ca10(PO4)6(OH)2 to show two formula units. It is the main mineral phase of human bone and tooth enamel, where it gives hardness and stiffness to otherwise organic tissues.
Hydroxyapatite is also called hydroxylapatite or calcium hydroxyphosphate.
Structure and Chemistry
Hydroxyapatite is made from calcium, phosphate, and hydroxide ions arranged in a crystalline lattice. In biological tissues, the mineral is not perfectly pure. Bone and enamel apatite can contain carbonate, magnesium, sodium, fluoride, and other substitutions that affect crystal size, solubility, and mechanical properties.
In bone, hydroxyapatite crystals are embedded in a collagen-rich matrix. In tooth enamel, apatite crystals are packed far more densely, giving enamel its hardness.
Bone and Teeth
More than 99 percent of the body's calcium is found in bones and teeth, mainly as calcium hydroxyapatite. Bone mineral provides compressive strength, while collagen provides toughness and flexibility.
Enamel is the hardest tissue in the human body and is highly mineralised. Dentine and bone contain more organic matrix and water, which makes them less hard but less brittle.
Medical and Dental Uses
Synthetic hydroxyapatite is used or studied in:
- Bone graft substitutes and bone fillers.
- Coatings for orthopaedic and dental implants.
- Tissue engineering scaffolds.
- Dental remineralisation products.
- Desensitising and enamel-repair toothpaste formulations.
Its appeal is that it resembles the mineral part of bone and teeth and can be biocompatible. Performance still depends on particle size, porosity, purity, manufacturing method, and the clinical use.
Dental Remineralisation
Nano-hydroxyapatite and related formulations are used in some toothpastes and dental products. Research suggests that hydroxyapatite can support remineralisation of early enamel lesions and may help with sensitivity in some settings.
It should not be treated as a replacement for basic dental prevention. Fluoride, sugar frequency, brushing technique, plaque control, saliva, and dental review remain important.
Synthesis
Hydroxyapatite can be made by wet chemical precipitation, sol-gel methods, hydrothermal methods, and processing of biological materials. Medical-grade material needs control of composition, contamination, crystal size, and sterilisation.
See Also
References
- PubChem: Calcium hydroxide phosphate
- NCBI Bookshelf: Dietary Reference Intakes for calcium and vitamin D
- NCBI Bookshelf: Hydroxyapatite dental material
- BDJ Open: Hydroxyapatite toothpaste and dental caries
- Dentistry Journal: Nano-hydroxyapatite and dental remineralisation
- American Chemical Society: Hydroxyapatite
Discussion log
Use comments for sourcing notes, corrections, and disputed details.
No comments yet.