The Formation of Hydroxyapatite-Ionomer Cements at 38°C

Abstract

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.