Chemical biofilm removal capacity of endodontic irrigants as a function of biofilm structure: optical coherence tomography, confocal microscopy and viscoelasticity determination as integrated assessment tools.

F H Busanello,P K Sharma,M V R So,X Petridis,R J B Dijkstra,L W M Van Der Sluis

doi:10.1111/iej.13027

Abstract

To investigate the influence of biofilm structure on the biofilm removal capacity of endodontic irrigants and to study changes in the architecture of the remaining biofilms. Streptococcus oralis J22 and Actinomyces naeslundii T14V-J1 were cocultured under different growth conditions on saliva-coated hydroxyapatite discs. A constant depth film fermenter (CDFF) was used to grow steady-state 4-day biofilms. Biofilms were grown under static conditions for 4 and 10days within a confined space. Twenty microlitres of 2% NaOCl, 2% Chlorhexidine (CHX), 17% Ethylene-diamine-tetra-acetic acid (EDTA) and buffer were applied statically on the biofilms for 60s. Biofilm removal was evaluated with optical coherence tomography (OCT). Post-treated biofilms were assessed via low load compression testing (LLCT) and Confocal laser scanning microscopy (CLSM). Optical coherence tomography data were analysed through a two-way analysis of variance (ANOVA). Low load compression testing and CLSM data were analysed through one-way ANOVA and Dunnett's post hoc test. The level of significance was set at a<0.05. The initial biofilm structure affected the biofilm removal capacity of the irrigants. NaOCl demonstrated the greatest chemical efficacy against the biofilms and was significantly more effective on the static than the CDFF biofilms (P<0.001). CHX was ineffective and caused a rearrangement of the biofilm structure. Ethylene-diamine-tetra-acetic acid exhibited a distinct removal effect only on the CDFF biofilms. Biofilm age influenced the structure of the remaining biofilms. The 4-day grown remaining biofilms had a significantly different viscoelastic pattern compared to the respective 10-day grown biofilms (P≤0.01), especially in the NaOCl-treated group. Confocal laser scanning microscopy analysis confirmed the CHX-induced biofilm structural rearrangement. Biofilm structure is an influential factor on the chemical efficacy of endodontic irrigants. Optical coherence tomography allows biofilm removal characteristics to be studied. NaOCl should remain the primary irrigant. Ethylene-diamine-tetra-acetic acid was effective against cell-rich/EPS-poor biofilms. Chlorhexidine did not remove biofilm, but rather rearranged its structure.

Highlights

Apical periodontitis is the reaction of the host immune system to micro-organisms mainly located within the root canal system (Nair 2004)
Post-treated biofilms were assessed via low load compression testing (LLCT) and Confocal laser scanning microscopy (CLSM)
Biofilm structure is an influential factor on the chemical efficacy of endodontic irrigants

Summary

Introduction

Apical periodontitis is the reaction of the host immune system to micro-organisms mainly located within the root canal system (Nair 2004). Complete eradication of the microbial infection is the theoretical aim of root canal treatment, this has been considered as an unrealistic task due to the complex intraradicular anatomy and the biofilm mode of microbial colonization (Nair et al 2005, Ricucci & Siqueira 2010). Biofilms have a distinct structure comprised mainly of water, a matrix of extracellular polymeric substances (EPS) and the micro-organisms (Flemming & Wingender 2010). This structural organization determines the susceptibility of biofilms to biocides to a great extent. Investigating the biofilm structure itself and its response to various stresses is important (Xiao et al 2012, Koo et al 2013)

Results

Discussion

Conclusion