A Theoretical Analysis of the Effects of Plaque Thickness and Initial Salivary Sucrose Concentration on Diffusion of Sucrose into Dental Plaque and its Conversion to Acid During Salivary Clearance

Abstract

A mathematical model, written in FORTRAN, has been developed to simulate the interrelated processes of salivary sucrose clearance from the mouth, diffusion of sucrose into dental plaque, and conversion of sucrose to acid and glucan. Reaction of acid with enamel is not included in the model. A total of 28 parameters can be varied by the user, and the relative importance of the different factors affecting acid formation can be assessed. The output of the program gives sucrose and acid concentrations and pH at different depths within the plaque. The initial variables studied were plaque thickness, the salivary sucrose concentration, and the duration of exposure of the plaque to sucrose. Stephan curves typical of those recorded in vivo were generated by the model. With any particular salivary sucrose concentration, there was an optimum plaque thickness at which a minimum pH was achieved at the enamel surface, with very thin or thick plaque samples producing a smaller pH fall. With thick plaque, the minimum pH was often not achieved at the inner surface but at some intermediate depth, which may explain the location of early caries lesions in fissures. The extent of the pH fall at the inner surface and the duration of the pH-minimum region of the Stephan curve were directly related to the initial salivary sucrose concentration and to the duration of exposure to sucrose prior to normal salivary clearance. Simulation of a water rinse at as short a time as two min after the beginning of normal salivary sugar clearance showed that this procedure had only a very small effect on the shape of the Stephan curve.(ABSTRACT TRUNCATED AT 250 WORDS)

An in vitro System for the Analysis of Changes in Depth Distribution of Diffusates in Bacterial Films

“…The effects of varying the bacterial film thickness gave results similar to those reported by Macpherson and Dawes [1991a], who demonstrated that increased film thickness caused a higher minimum pH following a sucrose rinse, in agreement with the trends predicted by the computer model of Dawes and Dibdin [1986]. This confirmed the in vitro model system as suitable for measuring pH changes at the base of a cariogenic film.…”

“…This confirmed the in vitro model system as suitable for measuring pH changes at the base of a cariogenic film. In a thick plaque, most of the glucose will be metabolised in the outer layers if the exposure is short, leaving less available to produce acid in the lower layers so that the minimum pH experienced at the plaque/tooth interface [Dawes and Dibdin, 1986] will be raised. Measurements of lactate concentrations and its spatial distribution support this hypothesis.…”

The Surface Area of the Adult Human Mouth and Thickness of the Salivary Film Covering the Teeth and Oral Mucosa

“…This is about half the thickness that we have calculated, but this may be due to the fact that, in their technique, the cheek was displaced from its normal position in close contact with the buccal surfaces of the teeth. In any event, the plaque is certainly not covered by a thick layer of saliva, as has been implicitly assumed in models of diffusion of substances in and out of plaque (Lagerl6f et al, 1984;Dawes and Dibdin, 1986).…”

Comparison of in vivo Human Dental Plaque pH Changes within Artificial Fissures and at Interproximal Sites

“…Thus, the ISFE T fissure plaque model is an interesting sys tem for studying the in situ diffusion o f various mole cules through plaque. The diffusion o f fermentable substrates, plaque acids and buffers through plaques o f defined thickness can be accurately monitored and it should be possible to test some o f the theoretical plaque diffusion models which have been presented by other investigators [Dawes and Dibdin, 1986], In addition, it is possible to use this system to study the effect of bacterial composition on plaque diffusion.…”