How Antimicrobial Photodynamic Therapy Can Affect Oral Biofilms?

Objectives: The objective of this study was to evaluate the effect of antimicrobial photodynamic therapy (aPDT) using a photosensitizer under different concentrations irradiated by a blue LED with 15J/cm² over different generations of Streptococcus mutans biofilm.
Methods: The S. mutans biofilm was induced over bovine enamel blocks (3x3x2mm) for 7 days (n=315). For aPDT curcumin-based photosensitizer under 20, 40 and 80μM) and one blue LED device (BioTable^®, 440nm, 36.1mW/cm²) was used. Different conditions were tested: a) LED (L) + photosensitizer (PS) under different concentrations (PS+L+); b) only LED (PS-L+); c) only photosensitizer (PS+L-, dark citotoxicity); d) without LED and photosensitizer (PS-L-, Negative Control Group) and e) application of chlorhexidine digluconate (C, Positive Control Group). All the different treatments were carried out over different generations of S. mutans biofilm (0, 6, 8, 12 and 24 hours after the first application of aPDT). After different treatments, the strains were plated on BHI agar to determine the number of colony forming units (CFU/mL). Also, the survival percentage was calculated. Biofilms of each control and experimental Groups (n=51) were taken for observation at confocal microscopy, and qualitative analyzes were obtained as to the distribution of non-viable viable/cells using LIVE/DEAD^® Baclight™ before and after different treatments. For CFU/mL and survival porcentage, the data were submitted to analysis of variance (ANOVA) and Tukey's test at 5% significance.
Results: It was observed that there was statistically significant difference in all Groups where aPDT and chlorhexidine digluconate solution were applied (p<0.05). For the Groups where only the PS was used (dark citotoxicity), no significant difference was observed compared to the negative control Group (p>0.05). Regarding the different generations of the S.mutans biofilm, just after 24hs, it was not observed statistically significant difference (p>0.05). Under 20μM, the log reduction observed was from 1 to almost 3 log.
Conclusions: aPDT using curcumin under 20μM associated with 15J/cm² can be an effective method to control S. mutans biofilm regardless of the different generations of the biofilm tested. Also, aPDT can be effective instead of the use of chlorhexidine digluconate.