Antimicrobial Photodynamic Therapy against Endodontic Enterococcus faecalis and Candida albicans Mono and Mixed Biofilms in the Presence of Photosensitizers: A Comparative Study with Classical Endodontic Irrigants.

Patrícia Diogo,João M Santos,Kleber T De Oliveira,M A F Faustino,Marciana P Uliana,Chantal Fernandes,M G P M S Neves,Teresa Gonçalves,Francisco Caramelo,Marta Mota,Isabel M Miranda

doi:10.3389/fmicb.2017.00498

Abstract

Endodontic biofilms eradication from the infected root canal system remains as the primary focus in endodontic field. In this study, it was assessed the efficacy of antimicrobial Photodynamic Therapy (aPDT) with the Zn(II)chlorin e6 methyl ester (Zn(II)e6Me) activated by red light against monospecies and mixed biofilms of Enterococcus faecalis and Candida albicans. The results were compared with the ones obtained with Rose Bengal (RB), Toluidine Blue-O (TBO), the synthetic tetracationic porphyrin (TMPyP) as well as classical endodontic irrigants (3% NaOCl, 17% EDTA and 2% CHX). The antimicrobial efficacy of aPDT toward monospecies and mixed biofilms was quantified resorting to safranin red method. The changes of biofilm organization and of cellular ultrastructure were evaluated through several microscopy techniques (light, laser confocal and transmission electron microscopy). Zn(II)e6Me once activated with light for 60 or 90 s was able to remove around 60% of the biofilm’s biomass. It was more efficient than TBO and RB and showed similar efficiency to TMPyP and classical irrigants, CHX and EDTA. As desirable in a PS, Zn(II)e6Me in the dark showed smaller activity than TMPyP. Only NaOCl revealed higher efficiency, with 70–90% of the biofilm’s biomass removal. The organization of biofilms and the normal microbial cell ultrastructure were extensively damaged by the presence of Zn(II)e6Me. aPDT with Zn(II)e6Me showed to be an efficient antimicrobial strategy deserving further studies leading to a future clinical usage in endodontic disinfection.

Highlights

Apical periodontitis is an inflammatory reaction of periradicular tissues caused by a microbial infection in the root canal system (Siqueira et al, 2000; Nair, 2006)
Before initiating the comparative study of the efficacy of antimicrobial Photodynamic Therapy (aPDT) and classical irrigants in the clearance of biofilms, it was important to verify if the PSs selected, Toluidine Blue-O (TBO), Rose Bengal (RB), TMPyP, and Zn(II)e6Me, had the ability to disturb the biofilms in the dark at the same concentration used in the aPDT studies
It was clearly desirable that the PSs had zero or very low activity in total absence of light indicating that aPDT efficacy resulted strictly from the reactive oxygen species (ROS) generated by PS light activation

Summary

Introduction

Apical periodontitis is an inflammatory reaction of periradicular tissues caused by a microbial infection in the root canal system (Siqueira et al, 2000; Nair, 2006). Microbial biofilms are considered the major cause for primary and secondary root canal infection and the success of endodontic treatment relies on the effective eradication of such biofilms (Nair, 2006). This is accomplished by chemo-mechanical disruption with instruments and antimicrobial chemicals used topically inside root canals. Current treatment strategies are insufficient to reduce microrganisms inside root canals below detection limits before permanent root filling. This is mandatory to achieve optimal healing conditions for the periapical tissues (Sjögren et al, 1997). Advanced disinfection approaches are required to effectively eradicate biofilms and increase the endodontic treatment success rate

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