Chemical efficacy of several NaOCl concentrations on biofilms of different architecture: new insights on NaOCl working mechanisms.

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

doi:10.1111/iej.13198

Abstract

AimTo investigate the anti‐biofilm efficacy and working mechanism of several NaOCl concentrations on dual‐species biofilms of different architecture as well as the changes induced on the architecture of the remaining biofilms.Methodology Streptococcus oralis J22 and Actinomyces naeslundii T14V‐J1 were co‐cultured under different growth conditions on saliva‐coated hydroxyapatite discs. A constant‐depth film fermenter (CDFF) was used to grow steady‐state, four‐day mature biofilms (dense architecture). Biofilms were grown under static conditions for 4 days within a confined space (less dense architecture). Twenty microlitres of buffer, 2‐, 5‐, and 10% NaOCl were applied statically on the biofilms for 60 s. Biofilm disruption and dissolution, as well as bubble formation, were evaluated with optical coherence tomography (OCT). The viscoelastic profile of the biofilms post‐treatment was assessed with low load compression testing (LLCT). The bacteria/extracellular polysaccharide (EPS) content of the biofilms was examined through confocal laser scanning microscopy (CLSM). OCT, LLCT and CLSM data were analysed through one‐way analysis of variance (ANOVA) and Tukey’s HSD post‐hoc test. Linear regression analysis was performed to test the correlation between bubble formation and NaOCl concentration. The level of significance was set at a < 0.05.ResultsThe experimental hypothesis according to which enhanced biofilm disruption, dissolution and bubble formation were anticipated with increasing NaOCl concentration was generally confirmed in both biofilm types. Distinct differences between the two biofilm types were noted with regard to NaOCl anti‐biofilm efficiency as well as the effect that the several NaOCl concentrations had on the viscoelasticity profile and the bacteria/EPS content. Along with the bubble generation patterns observed, these led to the formulation of a concentration and biofilm structure‐dependent theory of biofilm removal.ConclusionsBiofilm architecture seems to be an additional determining factor of the penetration capacity of NaOCl, and consequently of its anti‐biofilm efficiency.

Highlights

Sodium hypochlorite (NaOCl) is the main irrigant of choice during root canal treatment, with concentrations employed ranging between 0.5% and 6% (Slaus & Bottenberg 2002, Zehnder 2006, Dutner et al 2012, Savani et al 2014, Willershausen et al 2015)
Anti-biofilm efficacy of NaOCl concentrations assessed with optical coherence tomography
Four-day constant-depth film fermenter (CDFF) biofilms (4CDFFB) Treatment with 5% NaOCl significantly increased biofilm disruption compared to the control (P < 0.001), 2% NaOCl (P < 0.001) and 10% NaOCl (P < 0.001)

Summary

Introduction

Sodium hypochlorite (NaOCl) is the main irrigant of choice during root canal treatment, with concentrations employed ranging between 0.5% and 6% (Slaus & Bottenberg 2002, Zehnder 2006, Dutner et al 2012, Savani et al 2014, Willershausen et al 2015). Even though higher concentrations have been associated with improved treatment outcome, the level of evidence is weak (Fedorowicz et al 2012). Studies employing several biofilm models have shown a tendency towards increased biofilm removal with increasing NaOCl concentration (Arias-Moliz et al 2009, Retamozo et al 2010, Jiang et al 2011, Del Carpio-Perochena et al 2011). Contradictory results have been reported when lower NaOCl concentrations are applied. One per cent NaOCl has been shown to partially disrupt and decrease the viability of a biofilm (Chavez de Paz et al 2010, Del Carpio-Perochena et al 2011), whereas less or no effect at all has been reported (Retamozo et al 2010, Ordinola-Zapata et al 2012)

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