title: Ultrastructural changes of human dentin after irradiation by Nd:YAG laser.
abstract: OBJECTIVE
  The use of Nd:YAG laser has been proposed for endodontic treatment. However, its ability to reduce dentin permeability, which is important for the success of root canal treatment, remains controversial.
  
  
  METHODS
  Nd:YAG laser irradiation was performed in pulsed mode on human dentin. The parameters were: pulse energy (100 mJ), rate (10 pps), and total irradiation time (4 seconds). The crystalline phases, electron diffraction patterns, morphology, and microstructure of specimens after laser irradiation were observed by dark-field emission transmission electron microscope (TEM).
  
  
  RESULTS
  Three ultrastructural zones could be delineated in the dentin: (1) an outer zone with an ordered columnar structure composed of hydroxyapatite and beta-tricalcium phosphate, (2) an intermediate zone composed of an amorphous substance (about 40-70 nm in diameter), and (3) an inner zone of well-crystallized hydroxyapatite grains. These three zones were free of pores or voids.
  
  
  CONCLUSIONS
  Our study demonstrated that laser-irradiation might be used to reduce dentin permeability.
authors.affiliation: Department of Dentistry, National Taiwan University Hospital, Taipei 10016, Taiwan.
authors.forename: Bor Shiunn
authors.initials: BS
authors.lastname: Lee
authors.forename: Chun Pin
authors.initials: CP
authors.lastname: Lin
authors.forename: Feng Huei
authors.initials: FH
authors.lastname: Lin
authors.forename: Wan Hong
authors.initials: WH
authors.lastname: Lan
mesh_terms: D003745:Dental Enamel Permeability / Q000528:radiation effects*; D003804:Dentin / Q000528:radiation effects* / Q000648:ultrastructure*; D006801:Humans; D028022:Low-Level Light Therapy; D008854:Microscopy, Electron