The influence of salivary flow rate on diffusion of potassium chloride from artificial plaque at different sites in the mouth.

The rate at which substances diffuse from dental plaque influences the rate of clearance of acid and bacterial toxins from plaque into saliva. The aim of this study was to compare the rates of clearance of potassium chloride, as a model substance, from artificial plaque of 3-, 4-, and 6-mm-diameter, positioned bilaterally at different locations in the mouth. The diffusant was KCl (1 mol/L) in a 1.0% agarose matrix, placed in wells 1.5 mm deep, in small acrylic devices 3 mm thick, which could be fastened to the teeth with dental floss and removed after different time periods. The half-time for clearance was determined from the best-fitting least-squares line of the potassium concentration remaining in the gel plotted against the square root of time. For 14 subjects, half-times for the lower anterior lingual and upper posterior lingual regions averaged about 2.5 times greater than those for clearance into a large, stirred volume in vitro, whereas those for the upper and lower anterior buccal regions averaged about 12.8 times greater. This difference may be due to the fact that anterior buccal sites are exposed only to minor rather than to major salivary gland secretions. When salivary flow was stimulated by the sucking of sour lemon drops, all in vivo half-times were reduced by about one-half. The half-times were also directly related to the surface areas of the chambers, which implies that rates of diffusion from plaque of substances such as acid or bacterial toxins are inversely related to the surface area of the plaque at a particular site.