title: A new noninvasive model to study the effectiveness of dentin disinfection by using confocal laser scanning microscopy.
abstract: BACKGROUND
  The present study was designed to develop a standardized model for quantification of the effectiveness of dentin disinfection by different antibacterial solutions including a new root canal irrigant, Qmix.
  
  
  METHODS
  Dentinal tubules from the root canal side in semicylindrical dentin specimens were infected with Enterococcus faecalis by centrifugation of the bacterial suspension into the tubules. Scanning electron microscopy (SEM) was used to verify the presence of bacteria in dentin. The outer side of dentin pieces was closed, and the specimens were subjected to 1-minute and 3-minute exposure to sterile water, 1%, 2%, 6% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), and Qmix. Confocal laser scanning microscopy (CLSM) and viability staining were used to quantitatively analyze the proportions of dead and live bacteria inside dentin.
  
  
  RESULTS
  A heavy invasion by E. faecalis was detected by both SEM and CLSM throughout the dentinal tubules. The amount of dead cells in dentin increased with increasing NaOCl concentration and time of exposure (P < .05). Qmix was equally effective in killing bacteria in dentin as 6% NaOCl; more than 40% and 60% of the bacteria were killed by both at 1 minute and 3 minutes, respectively. One percent and 2% NaOCl and 2% CHX killed 20%-30% and 30%-40% bacteria after 1 and 3 minutes of exposure, respectively, with no statistically significant differences among the 3 agents (P > .05). In the control group, which was treated with sterile water, only 4%-6% of the bacteria were dead.
  
  
  CONCLUSIONS
  Centrifugation helped to create a heavy, evenly distributed infection deep into the dentinal tubules. The new model made it possible to compare the effectiveness of several disinfecting solutions in killing bacteria inside dentin by a noninvasive CLSM method.
authors.affiliation: Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Jingzhi
authors.initials: J
authors.lastname: Ma
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: D000891:Anti-Infective Agents, Local / Q000494:pharmacology; D001645:Biguanides / Q000494:pharmacology; D002498:Centrifugation; D002710:Chlorhexidine / Q000494:pharmacology; D003786:Dental Pulp Cavity / Q000382:microbiology; D003804:Dentin / Q000382:microbiology* / Q000648:ultrastructure; D013293:Enterococcus faecalis / Q000187:drug effects*; D006801:Humans; D018613:Microscopy, Confocal; D008954:Models, Biological; D011108:Polymers / Q000494:pharmacology; D012388:Root Canal Irrigants / Q000494:pharmacology*; D012973:Sodium Hypochlorite / Q000494:pharmacology
chemical_list: D000891:Anti-Infective Agents, Local; D001645:Biguanides; D011108:Polymers; C557698:QMix root canal irrigant; D012388:Root Canal Irrigants; D012973:Sodium Hypochlorite; D002710:Chlorhexidine