Red Fluorescence of Dental Biofilm as an Indicator for Assessing the Efficacy of Antimicrobials

Objectives: The aim of this study was to investigate whether the red fluorescence (RF) of dental biofilms detected by quantitative light-induced fluorescence (QLF) technology could be used to assess the efficacy of antimicrobials against biofilm cariogenicity.
Methods: Dental microcosm biofilms on bovine enamel discs were grown under 0.3% sucrose challenge and treated with different concentrations (0.05%, 0.1%, and 0.5%) of chlorhexidine digluconate (CHX) and distilled water (DW) twice daily for 7 days after initial saliva inoculation. Fluorescence images of the biofilms were taken by a QLF-Digital camera daily and the RF intensity was quantified by calculating the red/green ratio. After 7 days, the biofilm cariogenicity was assessed by measuring viable counts of total bacteria and aciduric bacteria, supernatant pH and the percentage of surface microhardness change (%SHC). Correlations between the RF and cariogenic properties according to the different concentrations of CHX were examined.
Results: The RF intensity of the CHX-treated biofilms, as well as the rate of increase in the intensity, was lower as compared to the DW-treated biofilms. Regarding the differences in the RF of the 7-d matured biofilms in the CHX groups, the RF intensity significantly decreased with increasing CHX concentrations (p < 0.001), with the intensity approximately 31% (0.05% CHX) to 46% (0.5% CHX) lower than that of the DW group. The RF intensity of the 7-d matured biofilms was also strongly associated with cariogenic properties, such as the number of total bacteria (r = 0.93, p < 0.001), number of aciduric bacteria (r = 0.97, p < 0.001), supernatant pH (r = 0.43, p = 0.01), and %SHC (r = 0.98, p < 0.001).
Conclusions: The detection of RF from dental biofilms using QLF technology can be used to assess and monitor the efficacy of antimicrobials non-destructively in real time.