Effect of particle size of metastable calcium phosphates on mechanical strength of a novel self-setting bioactive calcium phosphate cement.

Resistance to compressive strength after setting of the calcium phosphate cement consisting of tetracalcium phosphate (TECP), dicalcium phosphate dihydrate (DCPD), and 40 wt/wt% of a synthetic hydroxyapatite (HAP) was tested. An equimolar mixture of the calcium phosphate powder containing DCPD (particle diameter [D] 0.52-3.33 microns) and TECP (D, 1.1-13.1 microns) transformed into HAP at 37 degrees C, 100% RH after being mixed with 25 mM phosphoric acid. X-ray diffraction suggested that the cement containing fine particles of DCPD and TECP completely transformed to HAP, but that mixtures containing larger particles did not. Because particle size of both DCPD and TECP affected the compressive strength of the cement, the crystal growth of HAP during cement formation depended on the specific surface area (Sw) of the raw materials. The crystallite size of transformed HAP was estimated based on X-ray diffraction peaks at 25.8 and 32.8 degrees attributable to the 002 and 300 planes. The crystalline size attributable to the 300 plane decreased with increasing Sw, but that attributable to the 002 plane showed no significant relationship. The compressive strength of the cement after hardening increased with an increase of its Sw. This suggested that the harder calcium phosphate cement was (derived) from the smaller particle size of the raw materials.