In vitro aging of a calcium phosphate cement

Cement samples made of beta-tricalcium phoshate (beta-TCP), phosphoric acid (PA) and water mixtures were incubated in several aqueous solutions to det ermine their stability over time. The effects of the cement composition and the incubating temperature were investigated in more detail. The cement sa mples contained mostly dicalcium phosphate dihydrate (DCPD) and remnants of beta-TCP crystals. Depending on the initial cement composition, a certain amount of dicalcium phosphate (DCP) crystals were formed. The larger the in itial PA concentration, the larger the DCP amount. After setting, the cemen t composition was stable for at least 16 days up to 60 degrees C. Above tha t temperature, the DCPD crystals decomposed into DCP crystals. The latter r eaction provoked a decrease of the pH of the incubation solution, phenomeno n expected for a cement sample containing an excess of PA. As the cement sa mples contained an excess of beta-TCP, it was postulated that beta-TCP crys tals became so covered by DCP or DCPD crystals during setting that the sett ing reaction was stopped prematurely. The latter phenomenon gave a good exp lanation for the low pH values measured in the incubation solutions. (C) 20 00 Kluwer Academic Publishers.