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The Formation of Hydroxyapatite-Ionomer Cements at 38°C

Department of Materials Science, Penn State University, Materials Research Laboratory, University Park, Pennsylvania 16802

P.W. Brown

Department of Materials Science, Penn State University, Materials Research Laboratory, University Park, Pennsylvania 16802

This study describes the formation of a calcium polyacrylate-hydroxyapatite cement. Our hypothesis was that calcium phosphates would rapidly hydrolyze in the presence of polyacrylic acid (PAA) to form a cement. PAA, tetracalcium phosphate (TetCP), and dicalcium phosphate (DCP) were reacted together and formed calcium polyacrylate (CPA) and hydroxyapatite (HAp) within 10 h at 38°C, resulting in hardened masses. Reaction times increased with decreasing (HA preactants)/PAA ratios. In the first of three reaction stages, the pH increased while CPA and dicalcium phosphate dihydrate (DCPD) formed. Two steady-state pH conditions occurred during the second stage as TetCP reacted with DCPD and DCP. The first steady-state pH was the result of DCPD and TetCP reacting at near-equilibrium conditions. The second steady-state pH resulted as the reaction became limited by DCP dissolution. The third, diffusionally controlled, stage occurredas DCP and previously formed HA preacted to produce calcium-deficient HAp (Ca/P=1.5). The emphasis of this investigation was to establish the mechanistic path involved and the rate-limiting steps of the reaction.

Key Words: Hydroxyapatite • Composites • Polyacrylic Acid • Microstructure • and Kinetics.

Journal of Dental Research, Vol. 73, No. 3, 598-606 (1994)
DOI: 10.1177/00220345940730030501


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