Composition of Pooled Resting Plaque Fluid from Caries-free and Caries-susceptible Individuals

Abstract

The composition of pooled resting plaque fluid from 10 population samples, grouped according to age (8-11, 14-17, 18-25 years) and caries status (caries-free, CF, DMFS = 0; caries-susceptible, CS, DMFS > 10), was determined by means of ion chromatography. Subjects received a dental prophylaxis one week prior to plaque collection, abstained from oral hygiene for 48 hours, and did not eat or drink for at least one hour prior to plaque collection. Plaque samples from each group were pooled under mineral oil and centrifuged (15,000 g) for 45 minutes at ambient temperature. Supernatants were analyzed for organic acids, inorganic anions, mono- and divalent cations, and pH value. The ions Na⁺, NH₄⁺, K ⁺, Ca²⁺, Mg²⁺, Cl^-, and phosphate were present in all samples. Acetic and propionic acids were predominant, comprising over 75% of the acid (anions) present under resting conditions. Succinic, lactic, formic, and butyric acids were present in lower concentrations. Within each age group, the mean values for pH and NH₄⁺ concentration were higher in the caries-free group; the differences between mean values (CF: pH, 6.35 ; NH₄⁺, 52 mmollL; CS: pH, 5.85 ; NH ₄⁺, 37 mmol/L) were found to be statistically significant (p < 0.05) when all data for the CF and CS groups were combined. Significantly higher concentrations of Mg²⁺ and butyric acid were also found for the combined CF data. Concentrations of all other constituents were similar. Calculations indicate that plaque fluid is supersaturated with respect to enamel mineral and dicalcium phosphate dihydrate, with a significantly higher degree of saturation with respect to enamel mineral in the CF group. These results suggest that resting plaque fluid from CF individuals has a greater remineralization potential than that from CS individuals. It is suggested that the noted difference in saturation status is related to differences in plaque pH, resulting from differences in NH₃ production, which may reflect the presence of different bacterial species and residual energy sources.