Initial solubility and durability of polymeric calcium phosphate cements

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Mechanical strength and in vitro durability of four experimental and two commercial calcium phosphate dental cements were assessed. Hydroxyapatite formation processes in these calcium phosphate cements were also examined by means of x-ray diffraction analysis and their relationship with mechanical strength was discussed. The hydroxyapatite-forming polymeric calcium phosphate cements prepared from medium and fine tetracalcium phosphate powder and poly (methyl vinyl ether-maleic acid) showed lower compressive strength and higher flexural strength than the teracalcium phosphate cement prepared using poly (acrylic acid) and non hydroxyapatite-forming commercial α-tricalcium phosphate cements. The hydroxyapatite formation seemed to correspond to lowering in compressive strength of the cements based on tetracalcium phosphate and poly (methyl vinyl ether-maleic acid), while, in the case of the cement based on tetracalcium phosphate and poly (acrylic acid), no relationship was observed between the hydroxyapatite formation and the compressive strength. The hydroxyapatite-forming polymeric cements prepared using finely ground tetracalcium phosphate powder showed enhanced strength, even after prolonged immersion in water, compared to similar cements derived from the large sized tetracalcium phosphate. Initial solubility of both the experimental polymeric calcium phosphate cements seemed to be lower than that of the commercial calcium phosphate cements, which were prepared using organic acids.