Abstract
The aim of this study was to determine the variation in buffer capacity in dental plaque from different areas of the dentition that may be related to the caries status of associated tooth surfaces. Two-day plaque samples were collected from 8 different sites of 10 adult subjects living in Hokkaido ; upper-anterior-buccal (UAB) and lingual (UAL), upper-posterior-buccal (UPB) and lingual (UPL), lower-anterior-buccal (LAB) and lingual (LAL), lower-posterior-buccal (LPB) and lingual (LPL). Wet plaque samples were weighed and 25 mmol/L KCl were added to give a final concentration of 10mg/ml. The samples were dispersed with sonication and vortex mixing. A small stir bar was added to the suspension. A micro pH electrode was then applied and the pH was determined. The suspension was then titrated with 10mM-HCl to pH 3.0. Titration curves were expressed by the 3 rd order polynomial (y : pH, x : volume of acid added). Statistical analyses among 8 different sites were carried out using the ANOVA and Scheffe's test. The highest pH without acid was LAL (7.33±0.37 SD) and the lowest were LPB (6.61±0.25 SD) and UAB (6.62±0.40 SD) with statistical significances (p<0.0001). Significant differences were seen in the volume of acid added from pH 6.5 to 5.5, as well as from pH 5.5 to 3.0. Plaque associated with the LAL, which is very prone to saliva and less prone to caries, had the significantly highest volume of acid added in pH 6.5-5.5 (102.10±23.63 SE nmolH^+/mg plaque, p<0.01) and in pH 5.5-3.0 (435.32±77.25 SE nmolH^+/mg plaque, p<0.01), respectively. Compared to the other sites, LAL will maintain a higher pH and be more likely to precipitate some constituents affecting the plaque buffer capacity due to rapid salivary clearance. On the other hand, plaque in UAB seems to be the most caries susceptible because of the lowest buffer capacity, when examined, of any under-critical pH area. The results indicated that site-specific plaque buffer capacity which may reflect the differences in exposure to saliva, has been shown to be a possible cause of differences in local cariostatic challenge.
