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 INTRAORAL SITES

Variation in salivary access to different intra-oral sites is an impor tant factor in the site-dependence of dental caries. This study explor ed, theoretically, how access is modified by chewing sugar-free and su gar-containing gums. A finite difference computer model, described els ewhere, was used. This allowed for diffusion and/or reaction of substr ate, acid product, salivary buffers, and fixed-acid groups. Site-depen dent saliva/plaque exchange was modeled in terms of a 100-mu m-thick s alivary film covering the plaque (a) flowing directly from the salivar y ducts, (b) flowing from the intra-oral salivary pool, or (c) exchang ing with the pool. Computed flow-velocities or rates of exchange were based on previous intra-oral measurements. The model was also tested a gainst 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 sugges ted that: (1) although sugar-free gum chewed during a cariogenic chall enge causes a rapid rise in plaque pH, sucrose-containing gums cause t he pH, after a temporary rise resulting from increased salivary now, t o stay low for an extended period; (2) the computer model reproduced i n vitro tests reasonably well; (3) although the three models of the pl aque/saliva interaction start from different assumptions, two lead to closely related predictions; and (4) increasing the assumed salivary f ilm thickness by a large amount (e.g., from 50 to 200 mu m) caused no change in modeled Stephan curves, as long as these changes were accomp anied by appropriate reductions in film velocity, in accord, theoretic ally, with the practical clearance data.