Methods: Samples of dental plaque and whole saliva were collected from adults and children with various caries activity. Prior to sampling, the subjects refrained from any oral hygiene measure for 3 days. Suspensions of the dental plaque or the salivary sediment in MOPS (pH 7.0) or MES (pH 5.5) buffer solution containing glucose and inorganic salts were incubated aerobically at 37 °C for up to 20 min. The amounts of D- and L-lactic acid produced were determined enzymatically and the acid production was calculated in relation to the amount of plaque or salivary sediment and the incubation time. The acid production at pH 7.0 was defined as the acidogenic potential of the sample, while the ratio of the acid production at pH 5.5 by the acid production at pH 7.0 was considered indicative of its relative aciduric potential.
Results: For the adults, the acidogenic potential of plaque varied from 0.53 to 3.65 mg lactic acid/mg plaque and for the salivary sediment from 1.52 to 9.79 mg lactic/ml saliva. The corresponding values for plaque from children were 0.97 to 3.20 mg lactic/mg plaque. L-lactic acid was the dominant form in most samples, comprising about 70% of the total. The relative aciduric potential varied from 0.31 to 0.96 for the adults and 0.15 to 0.82 for the children. The acidogenic potential at pH 7.0 and pH 5.5 tended to be higher for samples taken from subjects with active caries lesions.
Conclusion: The acidogenic and aciduric potentials of human dental plaque and salivary sediment considerably vary among the subjects, the latter being higher than the former.