Journal of Dental Research, Vol 55, 496-505, Copyright © 1976 by International & American Associations for Dental Research Online Journals
Kinetics and mechanism of hydroxyapatite crystal dissolution in weak acid buffers using the rotating disk method
M. S. Wu, W. I. Higuchi, J. L. Fox and M. Friedman
The model given in this report and the rotating disk method provide a
useful combination in the study of dental enamel and hydroxyapatite
dissolution kinetics. The present approach is a significant improvement
over earlier studies, and both the ionic activity product that governs the
dissolution reaction and the apparent surface dissolution reaction rate
constant may be simultaneously obtained. Thus, these investigations have
established the baseline for the dissolution rate studies under sink
conditions. Concurrent studies, under conditions where the acidic buffer
mediums are partially saturated with respect to hydroxyapatite have shown
another dissolution site for hydroxyapatite that operates at a higher ionic
activity product but has a much smaller apparent surface reaction rate
constant. This has raised the question of whether the presence of this
second site may interfere with the proper theoretical analysis of the
experimental results obtained under sink conditions. A preliminary analysis
of the two-site model has shown that the dissolution kinetics of
hydroxyapatite under sink conditions is almost completely governed by the
sink condition site (KHAP = 10(-124.5), k' = 174) established in this
report. The difference between the predicted dissolution rate for the
one-site model and the two-site model are generally of the order of 4 to 5%
where the experiments are conducted under sink conditions and over the
range of variables covered in the present study.
