Journal of Dental Research, Vol 66, 1425-1430, Copyright © 1987 by International & American Associations for Dental Research Online Journals
Effect of acid type on kinetics and mechanism of dental enamel demineralization
M. V. Patel, J. L. Fox and W. I. Higuchi
The influence of acid type (pKa effects) of weak organic acid buffers on
dissolution kinetics of dental enamel was critically examined for rigorous
testing of the behavioral validity of the physical model of Patel et al.
(1987). Quantitative evaluation of this model indicated that monitoring
initial dissolution rates was a viable approach to critical testing of the
model. Initial dissolution rates were determined in 0.1 mol/L acetate (pKa
= 4.77), benzoate (pKa = 4.20), and salicylate (pKa = 2.98) buffers (pH =
4.50, mu = 0.50), with ground bovine enamel blocks of known surface area
mounted in a rotating disk apparatus. The Levich theory was used to study
dependence of dissolution rates on stirring rates in these buffers. The
experimental data were analyzed by the physical model which includes pKa
effects, complexation of the buffer anion with the other ions, surface
kinetics, simultaneous diffusion and equilibrium of all species in enamel
pores, diffusion layer thickness, and bulk solution composition. The KIAP
(formula: see text) governing the dissolution reaction and the surface
resistance factor were deduced from the model. Dissolution kinetics was
also followed in these buffers in the presence of calcium or phosphate
common ions. In effect, by conducting both the stirring rate studies and
common ion experiments, we derived the driving force function independently
by these two techniques. The results obtained in this study were consistent
with the model, indicating that pKa effects on the dissolution of dental
enamel can be accounted for quantitatively by the model, and it was found
that weak acids do not influence either the apparent solubility or the
surface reaction process of bovine dental enamel.
