title: Morphologic changes correlating to different sensitivities of Escherichia coli and enterococcus faecalis to Nd:YAG laser irradiation through dentin.
abstract: OBJECTIVE
  Previous studies demonstrated the disinfecting potential of Nd:YAG laser irradiation on the root canal system from an overall quantitative viewpoint. The aim of this study was to evaluate the specific effect of irradiation through dentin on gram-negative and gram-positive bacteria with regard to their cell structure.
  
  
  METHODS
  Sterile dentin samples of standardized size were divided into two sets of four groups with eight samples each. The first set was inoculated with Escherichia coli as the gram-negative test strain, the second set was inoculated with Enterococcus faecalis, which served as the gram-positive test organism. The samples were then irradiated on the bacteria-free side in contact mode under constant scanning movement at an angle of 10 degrees by use of the fiber optic of the Nd:YAG laser. Upon laser treatment they were critical point dried and subjected to SEM investigation. Another two sets of samples were prepared and irradiated in the same manner and evaluated by standard microbiological procedures to verify whether the observed morphologic alterations correlated to cell death.
  
  
  RESULTS
  SEM investigations revealed damage pattens that increased with the amount of energy applied. Whereas the gram-negative test organism showed immediate structural injury, the gram-positive test organism required repeated application of irradiation. The microbiological examination showed reduction of both bacterial strains, yet to different extents.
  
  
  CONCLUSIONS
  Our study demonstrates the different morphologic impact of Nd:YAG laser irradiation through dentin on representatives of the two main groups of bacteria. It shows that the construction of the cell wall is crucial for their individual sensitivity to laser treatment.
authors.affiliation: Department of Conservative Dentistry, Dental School, University of Vienna, A-1090 Vienna, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Moritz
authors.forename: S
authors.initials: S
authors.lastname: Jakolitsch
authors.forename: K
authors.initials: K
authors.lastname: Goharkhay
authors.forename: U
authors.initials: U
authors.lastname: Schoop
authors.forename: W
authors.initials: W
authors.lastname: Kluger
authors.forename: R
authors.initials: R
authors.lastname: Mallinger
authors.forename: W
authors.initials: W
authors.lastname: Sperr
authors.forename: A
authors.initials: A
authors.lastname: Georgopoulos
mesh_terms: D015169:Colony Count, Microbial; D003804:Dentin / Q000382:microbiology / Q000528:radiation effects*; D004203:Disinfection / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D013293:Enterococcus faecalis / Q000528:radiation effects* / Q000648:ultrastructure; D004926:Escherichia coli / Q000528:radiation effects* / Q000648:ultrastructure; D006801:Humans; D007834:Lasers; D008855:Microscopy, Electron, Scanning