The presence of smear‐layer affects the antimicrobial action of root canal sealers

AIM To assess the chemical and microstructural characteristics of dentine after the use of two irrigation protocols and correlate this with the antimicrobial properties of HCSC and changes to the dentine structure / chemistry after sealer placement. METHODOLOGY Two irrigation protocols - Protocol A using 2% NaOCl used 5mL/5 min and Protocol B with 2% NaOCl (5mL/5 min) followed by 17% EDTA (5mL/3 min) were used to prepare dentine. The chemical and microstructural changes following irrigation were assessed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared (FT-IR) spectroscopy (n=5) on dentine obtained from the mid-root and coronal parts of extracted human teeth. Four sealers (AH Plus, BioRoot, MTA Fillapex, TotalFill) were characterized by SEM/EDS (n=3). The ability of the sealers to eradicate intratubular Enterococcus faecalis biofilms was assessed by live/dead dye and confocal laser scanning microscopy to measure the percentage of living cells. The effect of combined irrigation and root filling on the dentine was assessed by SEM and EDS analysis (n=5). Statistical analysis was undertaken using one-way ANOVA and a number of post hoc tests to detect intergroup differences. The F test was used for comparison of variances in the microbiology testing. RESULTS The use of NaOCl alone left the smear layer seemingly intact, with traces of chlorine remaining on dentine. The use of BioRoot sealer restored the calcium ion levels of dentine which are depleted by the irrigation with EDTA. BioRoot exhibited antimicrobial properties against intratubular bacteria even in the presence of smear layer (Protocol A). The smear layer removal improved the bactericidal effect of all sealers and Ca2+ leaching. The use of a chelating agent was important for the intratubular sealer penetration for AH Plus but not the other sealers. CONCLUSION The removal of smear layer was associated with greater penetration of AH Plus into the dentinal tubules but not for the penetration of HCSC sealers. BioRoot was a more effective sealer in reducing the bacterial load in the dentinal tubules than the other materials tested and the presence of smear layer did not affect its activity.