Journal of Dental Research, Vol 73, 598-606, Copyright © 1994 by International & American Associations for Dental Research Online Journals
The formation of hydroxyapatite-ionomer cements at 38 degrees C
K. S. TenHuisen and P. W. Brown
Department of Materials Science, Penn State University, University Park 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 degrees C, resulting in hardened masses. Reaction times
increased with decreasing (HApreactants)/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 occurred as 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.
