title: Er:YAG and alexandrite laser radiation propagation in root canal and its effect on bacteria.
abstract: OBJECTIVE
  The objective of this study was to compare the bactericidal effect of the Er:YAG (wavelength 2.94 microm) and the Alexandrite (wavelength 0.75 microm) laser radiation. The spreading laser energy in the surrounding hard dental tissues round the root canal was evaluated and the bactericidal effect of both these different laser wavelengths was analyzed.
  
  
  BACKGROUND
  The use of a laser to clean and shape the root canal space is the latest method used for cleaning of root canals. The interest in laser endodontics was concentrated on the possibility to extirpate the contents of the root canal, to sterilize and to "melt" the walls of the root canals. The previous reports were performed with CO2, excimer, argon, Nd:YAG, Ho:YAG, and Er:YAG lasers.
  
  
  METHODS
  Er:YAG laser system (2.94 microm, energy 100 mJ or 300 mJ, repetition rate 1 Hz, 30 pulses) and alexandrite laser system (0.75 microm, energy 250 mJ, repetition rate 1 Hz, 30 pulses) were prepared and three experimental arrangements were used during the measurements. First the energy transport through the tooth tissue was observed (frontal and side experimental setups) and then, the bactericidal effect was evaluated.
  
  
  RESULTS
  It was demonstrated that due to the absorption in the hydroxyapatite and water content in the dentin, the Er:YAG laser radiation is fully absorbed in the root canal wall. This direct influence of the radiation could be expected only close to the sapphire tip. It was found that the tissue, which was not directly affected by the laser radiation, cannot be disinfected by the subablative effect of Er:YAG laser radiation. In the second part of the experiment the real bactericidal effect of Er:YAG ablative energy (300 mJ) could be observed. It was also shown that the alexandrite laser radiation with a wavelength of 0.75 microm spreads through the canal system space and leaks into the surrounding tooth tissues. Both lasers have bactericidal effect.
  
  
  CONCLUSIONS
  The pulsed Er:YAG and alexandrite lasers can be efficiently used for killing dental bacteria but the spreading of their radiation in the tooth tissues are different.
authors.affiliation: Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering, Prague, Czech Republic.
authors.forename: H
authors.initials: H
authors.lastname: Jelínková
authors.forename: T
authors.initials: T
authors.lastname: Dostálová
authors.forename: J
authors.initials: J
authors.lastname: Dusková
authors.forename: M
authors.initials: M
authors.lastname: Krátký
authors.forename: M
authors.initials: M
authors.lastname: Miyagi
authors.forename: S
authors.initials: S
authors.lastname: Shoji
authors.forename: J
authors.initials: J
authors.lastname: Sulc
authors.forename: M
authors.initials: M
authors.lastname: Nemec
mesh_terms: D003786:Dental Pulp Cavity / Q000382:microbiology* / Q000528:radiation effects*; D006801:Humans; D066298:In Vitro Techniques; D007778:Lactobacillus / Q000302:isolation & purification / Q000528:radiation effects*; D007834:Lasers; D008837:Micrococcus / Q000302:isolation & purification / Q000528:radiation effects*; D009616:Nocardia asteroides / Q000302:isolation & purification / Q000528:radiation effects*; D013298:Streptococcus sanguis / Q000302:isolation & purification / Q000528:radiation effects*