The effectiveness of curcumin-mediated antimicrobial photodynamic therapy depends on pre-irradiation and biofilm growth times

Background: The aim of this study was to determine the influence of distinct pre-irradiation times (PIT) of curcumin on the effectiveness of antimicrobial photodynamic therapy (aPDT) against intact dentin caries biofilms grown for 3 or 5 days. Methods: The microcosm biofilms grew on non-fluorescent glass blocks immersed in McBain medium with 1% sucrose, using microaerophilic conditions at 37 degrees C for 3 or 5 days. The biofilms were treated by the association of 600 mu mol.L-1 curcumin using different pre-irradiation times (1, 2 or 5 min) combined with 0 or 75 J.cm(-2) blue LED. Then, the vitality of biofilms was determined by confocal scanning laser microscopy (CSLM), after being stained with the mixture of ethidium bromide and fluorescein diacetate. Statistical analysis was performed by two-way ANOVA and post-hoc Tukey tests, after arcsine transformation (P < 0,05). Results: In comparison to control, curcumin alone (PIT = 5 min) and all combinations of curcumin and LED reduced significantly the vitality of 3-day biofilms. Distinctly, only curcumin plus LED using PITs of 2 or 5 min were effective in reducing the vitality of 5-day biofilms. Conclusion: Curcumin-mediated aPDT significantly decreased the vitality of intact dentin caries microcosms grown during 3 or 5 days, although successful treatments of 5-day biofilms required longer PITs in comparison to their counterparts.