Correlation of Dental Plaque Acidogenicity and Acidurance with Caries Activity – Perspectives of the Ecological Plaque Hypothesis

The ecological plaque hypothesis for the aetiopathogenesis of caries implies a microbial shift towards a more acidogenic and aciduric dental plaque microflora, due to a frequent carbohydrate intake. Certain plaque bacteria exhibit metabolic activity, at a low pH. A correlation exists between the increased numbers of some aciduric bacterial species, e.g. mutans streptococci and lactobacilli, and caries activity. The aim of this study was to study the acidogenic (lactate production / mg plaque x min., at pH 7.0) and aciduric potential (lactate production at pH 5.5 / lactate production at pH 7.0) of dental plaque in relation to the caries activity. Samples of dental plaque were collected from fifteen caries free and fifteen caries active children. Plaque suspensions in Ringer’s solution containing 1% sucrose and buffered with 0.5 M MOPS (pH 7.0) or MES (pH 5.5) were incubated aerobically at 37 oC for 10-20 min. The production of lactic acid in the suspensions was determined by an enzymatic assay. In caries free children, significantly lower acidogenic potential at both pHs were recorded than in caries active children. The highest difference between the groups was in the acidogenic activity at neutral pH. On the contrary, the aciduric potential was lower in the caries active group than in the caries free. Caries activity correlated with the acidogenic potentials of dental plaque at both pH 7.0 and 5.5. A new perspective of the ecological plaque hypothesis based on the increased catabolic ability of plaque is proposed.