Site-specificity of Acid Production in Dental Plaque

Objectives: We have been studying the site-specificity of dental plaque cariogenecity that would be related to the caries status of associated tooth surfaces. Our previous study of plaque buffer capacity showed that the highest was the lower-anterior- lingual (LAL) and the lowest was the upper-anterior-buccal(UAB) when we compared the 8 different sites. The aim of this study was to clarify the two different sites of acid production in dental plaque by determining the plaque pH curves following sucrose exposure. Methods: Two-day plaque samples were collected from UAB and LAL in each of 9 adult subjects. Wet plaque samples were transferred to plastic sticks and immediately put into pre-weighed plastic tubes. The samples were weighed and 0.85% KCl solution (1mg wet plaque/100µl ) was added. A stir bar was then added to the plastic tubes. A micro pH electrode was then inserted and the pH was determined. After 5 minutes, 10% sucrose (1mg wet plaque/30µl) was added, plaque pH was then measured at 60 different time points(1-60 min), and the plaque pH curves were recorded. After plotting the curves, the area under each curve (AUC) was calculated. Mean pH values are reported as the log of the mean hydrogen ion activity (i.e., 10^-pH), and all statistical comparisons were made based on the hydrogen ion activities. Statistical analyses between 2 different sites were carried out using the Mann-Whitney U test. Results: Initial pH (without acid) of plaque in the LAL (mean±S.D.: 7.18±0.36) was significantly higher than in the UAB (6.12±0.36) (p<0.01). As for the AUC, the UAB (mean±S.D.: 8.02±7.06 (mmol/L•min)) was significantly larger than the LAL (0.52±0.64 (mmol/L•min)) (p<0.01). Conclusion: Plaque in the UAB is more cariogenic than in the LAL.