Antibacterial activity of chlorhexidine after final irrigation with ethanol: CLSM and culture-based method analysis

Effect of irrigation protocols on chemical smear layer formation over the post-space dentin

This study evaluated the effect of irrigation protocols using 95% ethanol (ET) or 1% peracetic acid (PA) prior the use of 2% chlorhexidine (CHX) compared to distilled water (DW) on the chemical smear layer (CSL) formation and incidence of open dentin tubules at the apical, medium, and cervical third of the post-space dentin. Scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) images were used. Forty bovine roots were endodontically treated. After, post-space preparation was performed and the roots were randomized in four groups (n = 10) according to the irrigation protocol: DW, CHX, CHX-ET and CHX-PA. The chemical composition of CSL and the incidence of open dentin tubules at the post-space thirds were evaluated by EDS (500× magnification) and SEM (2000× magnification) images, respectively. Data from chemical composition of CSL were descriptively analyzed, while the incidence of open dentin tubules was evaluated by scores and submitted to Kruskal-Wallis and Dunn test (p = .05). Cl, Bi, and Si were the chemical elements most found over the dentin after the irrigation with CHX and CHX-ET. Moreover, CHX and CHX-ET showed the highest incidence of CSL (p < .05), but without difference between them (p > .05), regardless of the post-space third. DW and CHX-PA showed similar incidence of CSL (p > .05). No difference on the incidence of open dentin tubules was found for any irrigation protocol and post-space third (p > .05). The use of 1% PA prior the post-space irrigation with CHX decrease the incidence of CSL. RESEARCH HIGHLIGHTS: The post-space irrigation with chlorhexidine results in the formation of chemical smear layer. Ethanol is not capable to remove the chemical smear layer. Peracetic acid is more effective to remove the chemical smear layer.

Quercetin as an Auxiliary Endodontic Irrigant for Root Canal Treatment: Anti-Biofilm and Dentin Collagen-Stabilizing Effects In Vitro

Bacterial reinfection and root fracture are the main culprits related to root canal treatment failure. This study aimed to assess the utility of quercetin solution as an adjunctive endodontic irrigant that does not weaken root canal dentin with commitment anti-biofilm activity and bio-safety. Based on a noninvasive dentin infection model, dentin tubules infected with Enterococcus faecalis (E. faecalis) were irrigated with sterile water (control group), and 0, 1, 2, 4 wt% quercetin-containing ethanol solutions. Live and dead bacteria percentages in E. faecalis biofilms were analyzed by confocal laser scanning microscopy (CLSM). Elastic modulus, hydroxyproline release and X-ray photoelectron spectroscopy (XPS) characterization were tested to evaluate the irrigants’ collagen-stabilizing effect. The cytotoxicity was tested by CCK-8 assay. Quercetin increased the proportion of dead bacteria volumes within E. faecalis and improved the flexural strength of dentin compared to control group (p < 0.05). Quercetin-treated dentin matrix had less elasticity loss and hydroxyproline release after collagenase degradation (p < 0.05). Moreover, quercetin solutions revealed an increase in the C-O peak area under both C1s and O1s narrow-scan spectra of XPS characterization, and no cytotoxicity (p > 0.05). Quercetin exhibited anti-biofilm activity, a collagen-stabilizing effect with cytocompatibility, supporting quercetin as a potential candidate for endodontic irrigant.

Effect of ethanol on the antimicrobial properties of chlorhexidine over oral biofilm

The aim of this study was to evaluate the effect of 95% ethanol irrigation, with 5 or 10 min of action, on the antibacterial properties of 2% chlorhexidine (CHX), on oral biofilm, evaluated with confocal laser scanning microscopy (CLSM). Oral biofilm development was induced in 80 sterilized bovine dentin blocks, distributed in two groups (5 or 10 min) and 4 subgroups, according to time and the solution used: Saline (SALINE5, SALINE10); Saline followed by CHX (SALINE/CHX5, SALINE/CHX10); Ethanol (ETHANOL5, ETHANOL10), Ethanol followed by CHX (ETHANOL/CHX5, ETHANOL/CHX10). The surface of the block was dyed with Live/Dead^® BacLight. Images from different areas were analyzed by BioImage L program. The total biovolum (µm³), biovolum of live cells (green), percentage of live cells of the thickness of the biofilm visualized in CLSM and on surface biofilm were evaluated. Total biovolum and biovolum of living cells showed similar results among the different groups (p > .05). The percentage of living cells in total thickness of the biofilm also was similar among the groups (p > .05), except ETHANOL5, SALINE/CHX10, ETHANOL10, and ETHANOL/CHX10 that showed lower percentage than SALINE5 (p < .05). The ETHANOL10 and ETHANOL/CHX10 also showed lower percentage of living cells than ETHANOL/CHX5 and SALINE10 (p < .05). In relation to biofilm surface, SALINE/CHX5, SALINE/CHX10, ETHANOL5, ETHANOL10, ETHANOL/CHX5, and ETHANOL/CHX10 showed a lower percentage of living cells percentage than SALINE5 and SALINE10 groups (p < .05). Therefore, ethanol has no effect on antimicrobial properties of 2% chlorhexidine, prior when used as endodontic irrigating solution.