Related Experiment Video
Updated: May 6, 2026
Evaluation of the Efficacy of Organic Peroxyacids for Eradicating Dairy Biofilms Using an Approach Combining Static and Dynamic Methods
Published on: December 9, 2022
Effect of smear layer against disinfection protocols on Enterococcus faecalis-infected dentin
Zhejun Wang1, Ya Shen, Markus Haapasalo
1Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada; The State Key Laboratory Breeding Base of Basic Science of Stomatology (Hubei-MOST) and Key Laboratory of Oral Biomedicine Ministry of Education, School and Hospital of Stomatology, Wuhan University, Wuhan, China.
Introduction:
This study examined the effect of the smear layer on the antibacterial effect of different disinfecting solutions in infected dentinal tubules.
Methods:
Cells of Enterococcus faecalis were forced into dentinal tubules according to a previously established protocol. After a 3-week incubation period of infected dentin blocks, a uniform smear layer was produced. Forty infected dentin specimens were prepared and subjected to 3 and 10 minutes of exposure to disinfecting solutions including sterile water, 2% and 6% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), 17% EDTA, and QMiX (Dentsply Tulsa Dental, Tulsa, OK). The following combinations were also included: 2% NaOCl + 2% CHX, 2% NaOCl + QMiX, 6% NaOCl + QMiX, and 6% NaOCl + 17% EDTA + 2% CHX. Four other dentin specimens similarly infected but with no smear layer were subjected to 3 minutes of exposure to 2% CHX and 6% NaOCl for comparison. Confocal laser scanning microscopy and viability staining were used to analyze the proportions of dead and live bacteria inside the dentin.
Results:
In the presence of a smear layer, 10 minutes of exposure to QMiX, 2% NaOCl + QMiX, 6% NaOCl + QMiX, and 6% NaOCl + 17% EDTA + 2% CHX resulted in significantly more dead bacteria than 3 minutes of exposure to these same disinfecting solutions (P < .05). No statistically significant difference between 3 and 10 minutes was found in other groups (P > .05); 6% NaOCl + QMiX and 6% NaOCl + 17% EDTA + 2% CHX showed the strongest antibacterial effect. In the absence of a smear layer, 2% CHX and 6% NaOCl killed significantly more bacteria than they did in the presence of a smear layer (P < .05).
Conclusions:
The smear layer reduces the effectiveness of disinfecting agents against E. faecalis in infected dentin. Solutions containing 6% NaOCl and/or QMiX showed the highest antibacterial activity.
