西暦2000年特別企画“20世紀のセラミックスを先導した論文”α-燐酸カルシウムの水和

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  • Millennial Special Leading Papers on Ceramics in the 20<sup>th</sup> Century: the Best of JCerSJ The Hydration of α-Tricalcium Phosphate
  • セイレキ 2000ネン トクベツ キカク The hydration of アルファ Tricalcium Phosphate

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It can 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.<br>Many researchers have long believed that tricalcium phosphate is stable in water. However, the authors of this paper reported that α-tricalcium phosphate (α-TCP) converts to hydroxyapatite in hot water (80-100°C) and produces hardened porous products. The main results were as follows: bulk densities of 0.9-1.2g/cm3, compressive strengths of 15-16MPa and diametral strengths of 2-3MPa. 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 if a similar phase change occurred.<br>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 α-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. 6, 1983).<br>Subsequently, many studies on cementing calcium phosphate materials have increasingly appeared in technical and medical journals. Details of the hydration reaction of α-TCP were clarified. The hydration-hardening of α-TCP was made even at room temperature using various additives, and its possibility as a practical cementing material was significantly improved. A mixture of α-TCP and calcium hydrogenphosphate dihydrate was found to have good hydration-hardening properties (H. Monma et al., J. Ceram. Soc. Japan, 96, 878 (1988)). This combination gave the following results; about a 10-min setting time, 50-60% porosity and 15-20MPa wet compressive strength. Presently, the compressive strength has been improved to 50-90MPa.<br>After this author's paper, the following studies were made. The mixture of tetracalcium phosphate and calcium hydrogenphosphate dihydrate first proposed by Brown and Chow has been continuously investigated by many researchers, and its hardening properties were improved by using dilute phosphoric acid and adding synthetic hydroxyapatite powder. About 470 kinds of combinations using various calcium phosphates, calcium carbonate, calcium oxide, sodium fluoride, calcium sulfate hemihydrate, etc., were evaluated, and some available combinations for use as cementing materials were developed as follows: Lemaitre et al. in 1987, Mirtchi et al. in 1990, Bermudez et al. in 1993, and Driessens et al. in 1994. The glassy powder in the system of CaO-SiO2-P2O5 was developed as a bioactive cementing material (Kokubo et al., 1991). Hardened porous materials prepared from these calcium phosphate cements also became important also as supports for drug delivery systems. At present, α-TCP-based cementing materials are being used a a dental pulp lining (Sankin Co. Ltd., 1986), root canal filling (Sankin Co., Ltd., 1987) and osteoporosis filling (Mitsubishi Materials Co., Ltd., 2000).

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