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Abstract

The invention provides (i) a process for preparing tetracalcium phosphate particles, the process comprising the steps of (1) sintering or fusing a powder mixture at a temperature of not lower than 1,400.degree. C., the mixture comprising a powder of calcium source and a powder of phosphorus source in a Ca/P molar ratio of 2/1, and about 0.005 to about 5 parts of an aluminum compound, calculated as Al.sub.2 O.sub.3, per 100 parts of tetracalcium phosphate to be produced in terms of the theoretical amount, and (2) finely dividing the obtained product; (ii) tetracalcium phosphate particles prepared by said process; (iii) apatite-coated tetracalcium phosphate particles; (iv) a process for preparing the apatite-coated tetracalcium phosphate particles; (v) a tetracalcium phosphate-based setting composition; (vi) a composition for forming a hardening material using coated tetracalcium phosphate particles and an acidic aqueous solution; and (vii) the composition as defined in (vi) in which the acidic aqueous solution can satisfy the concentration relationships as represented below: (a) 25%.ltoreq.citric acid.ltoreq.50% (b) 30%.ltoreq.citric acid+phosphoric acid.ltoreq.70% (c) 10%.ltoreq.citric acid-phosphoric acid.ltoreq.50%

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First Claim