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Calcium Based Ceramic Hydrated Calcium Phosphate Hydroxyapatite (Ca10(PO4)6(OH)2)
Synthetic hydroxyapatite is chemically similar to the mineral component of bones and hard tissues in mammals. Hydroxyapatite is one of few materials that are classed as bioactive, which means that it supports osseointegration and bone ingrowth. It is used in orthopaedic, dental and maxillofacial applications.
The chemical nature of hydroxyapatite lends itself to substitution, which means that it is common for non-stoichiometric hydroxyapatites to exist. The most common substitutions are: carbonate, fluoride and chloride and those for hydroxyl groups, while defects can also exist resulting in deficient hydroxyapatites.
The main advantage of hydroxyapatite is the capability to integrate in bone structures and support bone ingrowth, without breaking down or dissolving. Hydroxyapatite is a thermally unstable compound. Depending on its stoichiometry, decomposition temperature varies from 800 to 1200 deg C.
Hydroxyapatite exists in forms such as powders, porous blocks or beads to fill bone defects or voids. Bone defects may arise when large sections of bone have to be removed (e.g. cancer) or when bone augmentations are required (e.g maxillofacial reconstructions or dental applications). The bone filler provides a scaffold and encourages fast filling of the void by naturally forming bone and providing an alternative to bone grafts. The bone filler becomes a part of the bone structure. The healing time is reduced compared to the situation if no bone filler was used (Hydroxyapatite).
The AZo Journal of Materials Online, available from www.azom.com (accessed October 31 2008)
Online source: Online Article