Effect of varying sediment and glucose concentrations on the pH and acid production in human salivary sediment mixtures

Abstract

The centrifugate (i.e. sediment) from paraffin-stimulated whole saliva, was reconstituted in various proportions with the liquid component of saliva. In this system, sediment and glucose concentrations were varied over a wide range, between 0–33.3% (v/v) and 0–30% (w/v) respectively, and pH-time curves for each of 42 combinations of concentrations were determined for a 4-hr period at 37 °C. The characteristics of the resulting pH curves were compared to the corresponding pH curves previously observed in plaque in situ and in the test-tube system of Stephan and Hemmens (1947). In spite of the dissimilarity in the cellular compositions of the different systems, pH curves were remarkably alike when sediment and substrate concentrations and system conditions were comparable. pH-Glucose concentration curves determined at each sediment concentration showed that, when the sediment concentrations were high, the pH-glucose concentration curve was almost identical to the same curve for plaque in situ. If the cell concentration was low, the curves differed in the region of high substrate concentrations. The relationship between pH and titratable acid for the many different combinations of substrate and sediment concentrations was also determined. Between approximately pH 6.7–8.7, the salivary system was poorly buffered and a single curve described this relationship. However, below 6.7, progressively increasing the sediment concentration progressively increased the buffering capacity of the salivary system so that multiple curves were necessary to describe the relationship between pH and titratable acid. The amount of acid necessary to reach a pH below 5.0 was considerably more when the sediment concentration was high than when it was low.