title: Bactericidal effect of different laser systems in the deep layers of dentin.
abstract: OBJECTIVE
  In recent years, various laser systems have gained importance in the field of laser-assisted endodontics, namely the Nd:YAG, the diode, the Er:YAG, and the Er,Cr:YSGG laser. Individual studies have been carried out so far, focusing on the respective wavelength, its specific bactericidal capabilities, and potential usefulness is root-canal disinfection. The present in vitro investigation however, was performed to compare the microbicidal effect of these laser systems under standardized conditions and to draw a conclusion upon their relative effectiveness in the deep layers of dentin.
  
  
  METHODS
  In total, 360 slices of root dentin with a thickness of 1 mm were obtained by longitudinal cuts of freshly extracted human premolars. The samples were steam sterilized and subsequently inoculated with a suspension of either Escherichia coli or Enterococcus faecalis. After the incubation, the samples were randomly assigned to the four different laser systems tested. Each laser group consisted of two different operational settings and a control. The dentinal samples underwent "indirect" laser irradiation through the dentin from the bacteria-free side and were then subjected to a classical quantitative microbiologic evaluation. To assess the temperature increase during the irradiation procedure, additional measurements were carried out using a thermocouple.
  
  
  RESULTS
  Microbiology indicated that all laser systems were capable of significant reductions in both test strains. At an effective output power of 1 W, E. coli was reduced by at least three log steps in most of the samples by the tested wavelengths, with the best results for the Er:YAG laser showing complete eradication of E. coli in 75% of the samples. E. faecalis, a stubborn invader of the root canal, showed minor changes in bacterial count at 1 W. Using the higher setting of 1.5 W, significant reductions of E. coli were again observed with all laser systems, where only the diode and the Er:YAG laser were capable of complete eradication of E. faecalis to a significant extent. There was no significant relation between the temperature increase and the bactericidal effect.
  
  
  CONCLUSIONS
  The present study demonstrates that all the wavelengths investigated are suitable for the disinfection of even the deeper layers of dentin and may prove to constitute valuable tools in state-of-the-art endodontics.
authors.affiliation: Department of Conservative Dentistry, Dental School, Medical University of Vienna, Währinger Street 25a, 1090 Vienna, Austria. curd.schoop@univie.ac.at
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schoop
authors.forename: Wolf
authors.initials: W
authors.lastname: Kluger
authors.forename: Andreas
authors.initials: A
authors.lastname: Moritz
authors.forename: Natascha
authors.initials: N
authors.lastname: Nedjelik
authors.forename: Apostolos
authors.initials: A
authors.lastname: Georgopoulos
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sperr
mesh_terms: D001419:Bacteria / Q000528:radiation effects*; D001424:Bacterial Infections / Q000517:prevention & control; D003804:Dentin / Q000528:radiation effects*; D006801:Humans; D007834:Lasers