title: Effect of smear layer against disinfection protocols on Enterococcus faecalis-infected dentin.
abstract: BACKGROUND
  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.
authors.affiliation: 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.
authors.forename: Zhejun
authors.initials: Z
authors.lastname: Wang
authors.forename: Ya
authors.initials: Y
authors.lastname: Shen
authors.forename: Markus
authors.initials: M
authors.lastname: Haapasalo
mesh_terms: D058491:Bacterial Load / Q000187:drug effects; D001431:Bacteriological Techniques; D001645:Biguanides / Q000008:administration & dosage / Q000494:pharmacology; D002710:Chlorhexidine / Q000008:administration & dosage / Q000494:pharmacology; D003786:Dental Pulp Cavity / Q000382:microbiology; D003804:Dentin / Q000382:microbiology* / Q000648:ultrastructure; D004203:Disinfection / Q000379:methods*; D004338:Drug Combinations; D004492:Edetic Acid / Q000008:administration & dosage / Q000494:pharmacology; D013293:Enterococcus faecalis / Q000187:drug effects*; D006801:Humans; D008422:Materials Testing; D050296:Microbial Viability / Q000187:drug effects; D018613:Microscopy, Confocal; D011108:Polymers / Q000008:administration & dosage / Q000494:pharmacology; D012388:Root Canal Irrigants / Q000008:administration & dosage / Q000494:pharmacology*; D016369:Smear Layer / Q000382:microbiology*; D012973:Sodium Hypochlorite / Q000008:administration & dosage / Q000494:pharmacology; D013997:Time Factors
chemical_list: D001645:Biguanides; D004338:Drug Combinations; D011108:Polymers; C557698:QMix root canal irrigant; D012388:Root Canal Irrigants; D004492:Edetic Acid; D012973:Sodium Hypochlorite; D002710:Chlorhexidine
keywords: Confocal laser scanning microscopy; Enterococcus faecalis; QMiX; dentin; disinfection; smear layer; sodium hypochlorite