Why Carbonate Apatite? Learning From the Human Bone

Abstract Body: Autografts have been considered as the gold standard for bone regeneration. However, availability of autografts harvested from the patient is limited. Thus, it often needs to be mixed with commercially available bone graft substitutes to obtain enough quantity of materials. Although the actual inorganic component of human bone is carbonate apatite, and carbonate group in the apatite structure is known to play an important role in bone remodeling, sintered hydroxyapatite has been used as typical bone graft substitute since carbonate apatite will decompose during sintering at high temperatures. Our group have developed a method to fabricate chemically pure carbonate apatite granules and blocks without sintering, allowing to control the amount of carbonate ion incorporated in apatite structure. Carbonate apatite fabricated by this method showed similar resorption characteristics to human bone, which is resorbed under weak acidic condition produced by osteoclasts and stable under neutral condition of body fluid. Osteoclastic resorption of carbonate apatite presents a good condition for new bone replacement based on the bone remodeling process. In contrast, pure hydroxyapatite remains stable under both acidic and neutral conditions, making the material non-resorbable. Osteoclastic resorption of the material has a close relationship with the activation of osteoblasts through cell-cell interaction, resulting in excellent osteoconductivity. Basic properties of carbonate apatite will be discussed in the presentation.