title: Effect of Nd:YAG laser irradiation on the hardness and elastic modulus of human dentin.
abstract: OBJECTIVE
  The purpose of this study was to investigate the changes of hardness and elastic modulus of human dentin after Nd:YAG laser irradiation.
  
  
  BACKGROUND
  The application of Nd:YAG laser in dental hard tissues has been widely studied. However, little information is available about the mechanical properties of teeth after Nd:YAG laser irradiation.
  
  
  METHODS
  The human dentin was irradiated by Nd:YAG laser through a 400-microm optic bare fiber. The parameters in laser delivery were 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec. Both the hardness and elastic modulus were obtained using an Instron microhardness tester and Vickers indenter. The indentations were then examined under a scanning electron microscope.
  
  
  RESULTS
  The hardness and elastic modulus of irradiated human dentin in the energy of 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec were 44.7 kg/mm(2) and 22.8 GPa, and 46.9 kg/mm(2) and 21.4 GPa, respectively. These values were significantly lower than that of non-irradiated dentin by the Student's t test.
  
  
  CONCLUSIONS
  Our study demonstrated that Nd:YAG laser irradiation would reduce the hardness and elastic modulus of human dentin.
authors.affiliation: Department of Endodontics, School of Dentistry, College of Medicine, National Taiwan University, Taipei, 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: Uei Ming
authors.initials: UM
authors.lastname: Li
authors.forename: Wan Hong
authors.initials: WH
authors.lastname: Lan
mesh_terms: D003804:Dentin / Q000528:radiation effects*; D004548:Elasticity / Q000528:radiation effects; D006244:Hardness / Q000528:radiation effects; D006801:Humans; D066298:In Vitro Techniques; D007834:Lasers