Microbiological aspects of an in situ model to study effects of antimicrobial agents on dental plaque ecology

This study validates an in situ model for ecological studies of dental plaq ue exposed to various antimicrobial agents with different modes of action o n plaque bacteria. Eleven subjects wore two acrylic appliances, each contai ning two bovine enamel discs, during two I-wk test periods. Using a split-m outh crossover design, the appliances were dipped twice daily for 1 min int o water (control; treatment A), fluoride (26.3 mM NaF; B), zinc acetate (20 .0 mM; C), or fluoride plus zinc acetate (D). Four of the subjects used als o chlorhexidine diacetate (2.2 mM; E) and chlorhexidine plus fluoride (F). At the end of each period, plaque was collected from the discs, after which the microbiota were analyzed by culture, automated quantitative immunofluo rescence, and a viability fluorescence stain. As compared to control, treat ments B, C, and D resulted in a significant reduction of individual taxa as detected by immunofluorescence, whereas similar bacterial viability and to tal bacterial numbers were observed. In contrast, chlorhexidine significant ly reduced bacterial viability, total cell numbers, and the abundance of mo st of the enumerated taxa. We conclude that this in situ model is well suit ed to study effects of antimicrobial agents on dental plaque ecology. Combi ned with viability testing, immunofluorescence is obviously superior to cul ture in detecting taxa-specific shifts caused by antimicrobial agents.