The hydration of .ALPHA.-tricalcium phosphate.

Abstract

be said that this article took the lead in studying a bioceramic group called ``calcium phosphate cement{''} or ``apatite cement.{''} The active promotion of calcium phosphate cementing materials has been made since the Monma-Kanazawa paper appeared. Many researchers have long believed that tricalcium phosphate is stable in water. However, the authors of this paper reported that alpha-tricalcium phosphate (alpha-TCP) converts to hydroxyapatite in hot water (80-100 degrees C) and produces hardened porous products. The main results were as follows: bulk densities of 0.9-1.2 g/cm(3), compressive strengths of 15-16 MPa and diametral strengths of 2-3 MPa. The resulting products were composed of calcium-deficient hydroxyapatites. This phenomenon was very peculiar since some other calcium phosphate did not show such a hardening property even ii a similar phase change occurred. Generally, cement-type materials possess many advantages different from densely sintered ceramics. If calcium phosphate cementing materials were created, they would be a significantly new type of calcium phosphate material and also to be bioactive. Therefore, this paper concerning the hydration-hardening of alpha TCP has attracted the attention of material researchers. At nearly the same time, the possibilities of various cementing calcium phosphate compositions were proposed by Brown and Chow based on thermodynamic considerations. The following two basic patents have been issued; H. Monma et al., ``Production of porous apatite,{''} Jpn. Pat.1103653 (Jul. 16, 1982), Appl. 53-124025 (Oct. 7, 1978) and W. E. Brown et al., ``Dental restorative cement: pastes, U. S. Pat. 45185430 (May 21, 1985), Appl. No. 539740 (Oct. 5, 1983). Subsequently, many studies on cementing calcium phosphate materials have increasingly appeared in technical and medical journals. Details of the hydration reaction of alpha-TCP were clarified. The hydration-hardening of alpha-TCP was made even at room temperature using various additives, and its possibility as a practical cementing material was significantly improved. A mixture of alpha-TCP and calcium hydrogenphosphate dihydrate was found to have good hydration-hardening properties (H. Monma et al., J. Ceram. Sec. Japan, 96, 878 (1988)). This combination gave the following results; about a 10-min setting time, 50-60% porosity and 15-20 MPa wet compressive strength. Presently, the compressive strength has been improved to 50-90 MPa. After this author's paper, the foll…