Carbonate apatite artificial bone

Bone apatite is not hydroxyapatite (HAp), it is carbonate apatite (CO₃Ap), which contains 6–9 mass% carbonate in an apatitic structure. The CO₃Ap block cannot be fabricated by sintering because of its thermal decomposition at the sintering temperature. Chemically pure (100%) CO₃Ap artificial bone was recently fabricated through a dissolution–precipitation reaction in an aqueous solution using a precursor, such as a calcium carbonate block. In this paper, methods of fabricating CO₃Ap artificial bone are reviewed along with their clinical and animal results. CO₃Ap artificial bone is resorbed by osteoclasts and upregulates the differentiation of osteoblasts. As a result, CO₃Ap demonstrates much higher osteoconductivity than HAp and is replaced by new bone via bone remodeling. Granular-type CO₃Ap artificial bone was approved for clinical use in Japan in 2017. Honeycomb-type CO₃Ap artificial bone is fabricated using an extruder and a CaCO₃ honeycomb block as a precursor. Honeycomb CO₃Ap artificial bone allows vertical bone augmentation. A CO₃Ap-coated titanium plate has also been fabricated using a CaCO₃-coated titanium plate as a precursor. The adhesive strength is as high as 76.8 MPa, with excellent tissue response and high osteoconductivity.