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Effect of Smear Layer against Disinfection Protocols on Enterococcus faecalis–infected Dentin

  • Zhejun Wang
    Affiliations
    Division 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
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  • Ya Shen
    Affiliations
    Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada
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  • Markus Haapasalo
    Correspondence
    Address requests for reprints to Dr Markus Haapasalo, Division of Endodontics, Oral Biological and Medical Sciences, UBC Faculty of Dentistry, 2199 Wesbrook Mall, Vancouver, BC, Canada V6T 1Z3.
    Affiliations
    Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada
    Search for articles by this author
Published:September 03, 2013DOI:https://doi.org/10.1016/j.joen.2013.05.007

      Abstract

      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.

      Key Words

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