The role of insoluble glucan as a diffusion barrier in dental plaque

Abstract

This study was designed to clarify the role of insoluble glucan produced by S. mutans in the caries-producing-process. In an apparatus set with an pH electrode and an extracted tooth, S. mutans PK 1 and its mutant diminished in insoluble glucan synthesis were continuously cultured for 40 hours. The wild-type cells formed much adhesive bacterial deposits, composed of abundant insoluble glucan. A gradient of pH between the deposits and the surrounding medium was observed during the culture. The mutant formed a significant amount of fragile deposits which contained much soluble glucan. However, no pH gradient was found between the medium and the deposits produced by the mutant. When the bacterial deposits in which the pH decreased to 4.5 were washed with a pH 7.0 buffer solution, the pH restored to neutral pH slowly in the wild type cells, but rapidly in the mutant cells. There was a significant difference in the degree of decalcification between wild cells-coated and mutant cells-coated enamels.These results demonstrate that the diffusion barrier created by the insoluble glucan produced by S. mutans plays a role in the caries-producing activity.