Journal of Dental Research, Vol 74, 1482-1488, Copyright © 1995 by International & American Associations for Dental Research Online Journals
Computer modeling of the effects of chewing sugar-free and sucrose-containing gums on the pH changes in dental plaque associated with a cariogenic challenge at different intra-oral sites
G. H. Dibdin, C. Dawes and L. M. Macpherson
MRC Dental Group, Dental School, Bristol, United Kingdom.
Variation in salivary access to different intra-oral sites is an important
factor in the site-dependence of dental caries. This study explored,
theoretically, how access is modified by chewing sugar-free and
sugar-containing gums. A finite difference computer model, described
elsewhere, was used. This allowed for diffusion and/or reaction of
substrate, acid product, salivary buffers, and fixed-acid groups.
Site-dependent saliva/plaque exchange was modeled in terms of a
100-microns-thick salivary film covering the plaque (a) flowing directly
from the salivary ducts, (b) flowing from the intra-oral salivary pool, or
(c) exchanging with the pool. Computed flow-velocities or rates of exchange
were based on previous intra-oral measurements. The model was also tested
against an in vitro study conducted by two of the authors. In addition, the
three proposed models of saliva/plaque interaction were compared, and the
effect of salivary film thickness investigate. Results suggested that: (1)
although sugar-free gum chewed during a cariogenic challenge causes a rapid
rise in plaque pH, sucrose-containing gums cause the pH, after a temporary
rise resulting from increased salivary flow, to stay low for an extended
period; (2) the computer model reproduced in vitro tests reasonably well;
(3) although the three models of the plaque/saliva interaction start from
different assumptions, two lead to closely related predictions; and (4)
increasing the assumed salivary film thickness by a large amount (e.g.,
from 50 to 200 microns) caused no change in modeled Stephan curves, as long
as these changes were accompanied by appropriate reductions in film
velocity, in accord, theoretically, with the practical clearance data.
