In vitro evaluation of photodynamic therapy associated with irrigation protocols in the control of multispecies endodontic biofilm.

AIM: To evaluate the antimicrobial efficacy of antimicrobial photodynamic therapy (aPDT), either alone or in combination with various irrigation protocols, against mature multispecies biofilms. MATERIALS AND METHODS: Multispecies biofilms consisting of nine bacterial species were cultivated on 72 bovine dentin discs and randomly assigned to six groups (n = 12 each): saline (control), saline + aPDT, 2.5% sodium hypochlorite (NaOCl) + 17% EDTA, NaOCl + EDTA + aPDT, 2% chlorhexidine (CHX) + EDTA, and CHX + EDTA + aPDT. aPDT was performed using 0.005% methylene blue and a red diode laser (660 nm, 100 mW, 9 J, 90 s). The antimicrobial efficacy was assessed through colony-forming unit (CFU) counts and confocal laser scanning microscopy (CLSM). The data were analyzed using a significance level of 5%. RESULTS: The saline control exhibited the highest microbial load, which was significantly reduced when combined with aPDT (p < 0.05). Both NaOCl and CHX, in the absence of aPDT, significantly decreased microbial levels compared to saline (p < 0.05). When used alongside aPDT, NaOCl resulted in the lowest CFU values; however, no additional antimicrobial benefit from light activation was observed. The antimicrobial reduction achieved with saline + aPDT was comparable to 2% CHX. CLSM analysis corroborated these findings. CONCLUSION: aPDT enhanced the antimicrobial efficacy of physiological saline, resulting in an antimicrobial effect comparable to that observed with 2% liquid chlorhexidine. Among the irrigation protocols evaluated, 2.5% sodium hypochlorite showed the greatest antimicrobial efficacy, with no significant additional benefit following the application of aPDT.