Ion-sensitive field-effect transistor (ISFET) pH electrodes were used to monitor changes in plaque pH at the base of artificial occlusal surface fissures and at interproximal sites. Bovine enamel was used to construct fissures (1.5 × 0.1 × 1.0 mm) containing a small ISFET electrode. The fissures were fixed to carrier appliances and worn by 4 human volunteers. After plaque accumulation for 4 days changes in pH were monitored by wire telemetry following 1-min rinses with 10% solutions of either sorbitol or sucrose. Results were compared to data obtained from interproximal sites in the same subjects. Responses to sorbitol in the fissure and on the proximal surfaces were minimal and showed no significant difference in minimum pH (5.9 ± 0.4 and 6.1 ± 0.3, respectively) and area under pH 7.0. The response to sucrose at the two sites was very different revealing unique pH profiles which were statistically significantly different with regard to minimum pH (5.0 ± 0.3, fissure and 4.3 ± 0.2, proximal) and area under pH 5.7. Thus, the acidogenic potential of fermentable carbohydrate at two caries-prone sites in the human dentition is significantly different and conclusions based on interproximal telemetry measurements may not be applicable to occlusal surface fissures.

Changes in sucrose-induced plaque pH profiles and the microbial composition of occlusal tooth surface fissures were analyzed using wire telemetry and bacterial culturing techniques. Four human volunteers wore appliances containing artificial fissures constructed with ion-sensitive field-effect transistor (ISFET) electrodes for 1 2 and 4 days; 1 subject kept the electrode for 3 weeks. After monitoring the plaque pH response at the base of the fissure to a 10% (w/v) sucrose rinse the plaque was removed and analyzed for total viable bacteria, total and specific streptococci, lactobacilli and Actinomyces spp. One-day-old plaque showed a rapid drop in plaque pH to a minimum of 4.8 ± 0.2, with 2-day-old plaque showing the most acidogenic pH profile (minimum pH 4.6 ± 0.2). The 4-day-old plaque response was less acidogenic (minimum pH 5.0 ± 0.3) than the results from days 1 and 2. Responses from 13- and 21-day-old fissure plaques showed greatly decreased acidogenic responses (day 21 minimum pH 5.7). Viable bacteria recovered from the fissure increased from approximately 4 × 10⁶ colony-forming units on day 1 to 1.2 × 10⁷ on days 2 and 4 and 1.7 × 10⁷ on day 21. Streptococci ( > 50%) and Actinomyces ( > 10%) dominated in the fissure plaques and their levels were related to minimum pH. Since fissure plaque of all ages tested contained high concentrations of acidogenic bacteria, the decreased acidogenic response at the base of fissures with increasing plaque age suggests that maturing fissure plaques provide an increasingly greater diffusion barrier to fermentable carbohydrates.