Hydroxyapatite thermal decomposition product which is a mixture of alpha-tricalcium phosphate and tetracalcium phosphate was investigated physically, chemically and biologically as a self-hardening type biomaterial. Hardening of the decomposition product mixing with water was caused by recrystallization of hydroxyapatite. Implanting in the femoral cavity of a rabbit, the hardened body bonded to the bone directly and new bone formed in the gaps between the cortical bone and the hardened body.

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... ition of citric acid improved the physical properties. In this case, an amorphous phase consisted of Ca-PO4-Cit-H2O system was formed. But the color of marrow bone around the hardened body changed into black. The reason of the color change was thought to be owing to excess dissolution of calcium ion which is an important factor of the blood coagulation. Further addition of trisodium citrate improved the color change, because the further added citrate ion cap tured the excess calcium ion. The hardened body also bonded to the bone directly and new bone formed.