title: Effect of pulsed Nd:YAG laser irradiation on acid demineralization of enamel and dentin.
abstract: OBJECTIVE
  The purpose of this study was to investigate the effect of Nd:YAG laser irradiation on the acid demineralization of enamel and dentin by spectrophotometry. A mechanism of acquired acid resistance is also proposed.
  
  
  BACKGROUND
  The ability of Nd:YAG laser irradiation to the enhanced resistance to artificial caries formation is still controversial.
  
  
  METHODS
  A pulsed Nd:YAG laser at 1.064-micron wavelength was used to irradiate the human enamel and dentin samples from 20 extracted human molars at the parameters of 1, 2, and 3 W and 20 pps for a total of 9 sec after painting with black ink. Samples were then subjected to 2 microliters of 0.1 M lactic acid solution (pH 4.8) for 24 h at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were also investigated by scanning electron microscopy (SEM).
  
  
  RESULTS
  The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, in those by irradiated at 2 W and 1 W. The unlased samples showed the highest Ca2+ ppm. SEM observation showed that in the lased areas, the smear layer was partially melted and the underlying primary enamel or dentin seemed to be thermally degenerated.
  
  
  CONCLUSIONS
  The results of this study suggested that melted smear layer and underlying enamel or dentin degenerated thermally by the heat treatment of Nd:YAG laser might play a major role to enhance resistance to artificial caries-like formation.
authors.affiliation: Department of Endodontics, Showa University School of Dentistry, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Hossain
authors.forename: Y
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Y
authors.initials: Y
authors.lastname: Kimura
authors.forename: Y
authors.initials: Y
authors.lastname: Yamada
authors.forename: T
authors.initials: T
authors.lastname: Kawanaka
authors.forename: K
authors.initials: K
authors.lastname: Matsumoto
mesh_terms: D002118:Calcium / Q000032:analysis; D003743:Dental Enamel / Q000528:radiation effects; D003804:Dentin / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D053685:Laser Therapy; D008855:Microscopy, Electron, Scanning; D008963:Molar; D016369:Smear Layer; D013053:Spectrophotometry / Q000379:methods; D018709:Statistics, Nonparametric; D017001:Tooth Demineralization / Q000517:prevention & control / Q000532:radiotherapy*
chemical_list: D002118:Calcium