Answer:
Hydroxyapatite (HA), or Ca10(PO4)6(OH)2, is the major inorganic constituent of bone. Corals create a calcium carbonate exoskeleton resembling human bone with an average pore size of 200 microns. Surgical vendors convert the calcium carbonate skeleton into HA through an exchange reaction of the carbonate for phosphate. The resultant material has the porous anatomy of bone with identical chemical composition. HA is capable of strongly bonding to adjacent bone. It has excellent maintenance of contour and volume and HA implants do not elicit a foreign body or inflammatory response.
HA is available in block form and as granules. It is most commonly used to augment the contour of the facial skeleton or as a bone graft substitute in orthognathic surgery. HA implants are rapidly invaded by fibrovascular tissue and there is histologic evidence of direct osseous union between implant and bone. HA is osteoconductive in that it provides a matrix for deposition of new bone from adjacent living bone, but it is not osteogenic, in that it will not induce new bone formation when placed in ectopic sites such as muscle or fat. Long term follow up radiographs do not show evidence of resorption.
Bonesource (Leibinger) is a synthetic HA cement that was first used clinically in 1991. When mixed with water and a drying agent (sodium phosphate) BoneSource powder forms a paste that hardens to from a microporous implant within 15 minutes. It is biocompatible with no inflammatory tissue response, and the infection rate is low. Over time, the HA cement maintains its shape and stimulates bony ingrowth from adjacent bone.
The PRS article, “The response of porous hydroxyapatite to contiguous tissue infection” (H. Rosen), describes two case reports in which infections in soft tissue adjacent to previously implanted HA were successfully treated with local debridement and 6 weeks of intravenous antibiotics, without having to remove the incorporated HA implant. They propose that infections in these implants can be successfully treated with systemic antibiotics due to the excellent vascularity of a well incorporated HA implant.