Hydroxyapatite (HA) is a calcium phosphate bioceramic material, which is the major component and an essential ingredient of mineral component (~70%) of bone and teeth. The first class of hydroxyapatites to be developed were synthetically produced in the 1970s. Excellent biocompatibility and osteoconductivity have led to a wide variety of applications in both dentistry and orthopaedics [1]. The osseointegration of an implant can be accelerated by a hydroxyapatite coating [2]. 

Osseointegration and synthetic bone

Hydroxyapatite largely consists of calcium and phosphorous. This composition allows it to function in the biomedical industry as a coating that promotes osseointegration between bone and various orthopedic implants. Hydroxyapatite is also used in hip, knee and other implants as a synthetic bone substitute as it helps promote bone ingrowth. Hydroxyapatite coating on implants, such as dental implants, were reported to precipitate faster bone fixation, which reduces pain and recovery time for patients. 

Dental and oral applications

Since the clinical success of dental implants depend on the osseointegration at the bone-implant interface, surfaces of bone-contacting devices would be desirable to be compositionally, structurally, and functionally analogous to that of human bone. 

Tooth enamel is almost all hydroxyapatite. Oral care products that incorporate this mineral have greatly improved dental practice for patients. It can be added to dental filling agents used to repair serious cavities. It also has been shown to reduce or eliminate tooth sensitivity after whitening. It has become an important tool in the periodontal and oral surgery specialties. Regular use of hydroxyapatite products can keep teeth healthy and avoid becoming demineralized in the first place. Products are formulated with bioavailable nanohydroxyapatite to provide the greatest cavity fighting and cavity preventing benefits to patients.

Drug delivery 

Biocompatibility, bioactivity, and osteoconductivity are the main driving forces of hydroxyapatite biomaterials, promoting their application as bone substitutes. At the same time, multimodal porous structure and interconnectivity of pores make them promising candidates for site-specific drug delivery. The use of porous hydroxyapatite as a drug delivery system could result in a dual effect: the ability to interact with the bone tissues at the same time ensuring increased drug efficiency, controlled release, and site-specific delivery.

Facial augmentation

Facial augmentation with hydroxyapatite has been used for the corrections of cheek, chin, jaw, nose and browbone. Solid hydroxyapatite can be carved and trimmed to the requirements of the correction. Because bone and soft tissue growth into the pores of the implant occurs quickly after implantation, the implant is securely held in place. Over time the implant is partially resorbed and replaced by natural bone. 

Others

Non-medical uses that have shown promise include air filtration to remove carbon dioxide and a filter to remove fluoride from saturated soil.
 

References

[1] T.J. Levingstone, Optimisation of plasma sprayed hydroxyapatite coatings: Dublin City University; 2008.
[2] https://www.medicoat.com/spray-powder/hydroxyapatite-powder/
[3] R.J. Havlik, P.D. Committee, Hydroxyapatite, Plastic and reconstructive surgery, 110(2002) 1176-9.
[4] L. Sheikh, M. Baripada, J. Burmamines, Synthesis and characterization of stable hydroxyapatite slurry, (2010).
[5] https://www.truthinaging.com/ingredients/hydroxyapatite
[6] M. Ferraz, F. Monteiro, C. Manuel, Hydroxyapatite nanoparticles: a review of preparation methodologies, Journal of Applied Biomaterials and Biomechanics, 2(2004) 74-80.
[7] B. de Caprariis, A. Chianese, M. Stoller, N. Verdone, Hydroxyapatite Production by an Intensification Process,  Hydroxyapatite-Advances in Composite Nanomaterials, Biomedical Applications and Its Technological Facets, InTech2018.