Ultrastructural analysis of structural framework in dental plaque developing on synthetic carbonate apatite applied to human tooth surfaces.

This study focused on determining the structural framework by oral microbiota in supragingival plaque on a carbonate apatite film applied to human tooth surfaces. The sequential phases of plaque formation over a 3-wk period were found to be equivalent to those previously reported for natural tooth surfaces. Scanning electron microscopy of specimens prepared by vertical sectioning demonstrated the organization of two types of framework between certain genera of initial and secondary colonizers in the pre- and post-organization phases, respectively. The initial colonizers in the pre-organization phase were of a coccoid type, while colonizers in the post-organization phase were of a bacillary type. Secondary colonizers, filamentous cells, were common to both frameworks. Transmission electron microscopy using freeze-substitution and immunohistochemistry demonstrated two types of coaggregation, fibril- and saliva-mediated modes, among the plaque microbiota. Coaggregation between microbiota, which organized the framework, showed a tendency to occur in the fibril-mediated mode, and the filamentous secondary colonizers were characterized by inducing multigeneric coaggregation. The present findings indicate that a structural framework and specific cells to form this framework are essential for plaque formation.