title: Acquired acid resistance of dental hard tissues by CO2 laser irradiation.
abstract: OBJECTIVE
  This investigation was performed to evaluate the effect of CO2 laser irradiation on the acquired acid resistance of dental hard tissues to artificial caries-like formation and the ultrastructure of lased areas was morphologically investigated in vitro.
  
  
  BACKGROUND
  In recent years, many studies have been carried out to evaluate the effect of the CO2 laser on the enhanced resistance to artificial caries formation of enamel. However, a limited number of papers concerning its effect on dentin have been published.
  
  
  METHODS
  A CO2 laser of 10.6 microns wavelength was used to irradiate human enamel and dentin samples from 20 extracted human molar teeth, and samples were 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 investigated by scanning electron microscopy (SEM).
  
  
  RESULTS
  The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, followed by 2 W, 1 W, and unlased samples. SEM observation showed that the lased areas were melting with solidification of the smear layer. Even after acid demineralization, the lased surfaces were almost unchanged.
  
  
  CONCLUSIONS
  The results of this study suggested that CO2 laser irradiation could sufficiently melt and solidify the enamel and dentin surfaces and thus 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: M
authors.initials: M
authors.lastname: Ito
authors.forename: Y
authors.initials: Y
authors.lastname: Yamada
authors.forename: K
authors.initials: K
authors.lastname: Matsumoto
mesh_terms: D000143:Acids / Q000009:adverse effects; D003731:Dental Caries / Q000209:etiology / Q000517:prevention & control; D006801:Humans; D007834:Lasers; D014070:Tooth / Q000528:radiation effects* / Q000648:ultrastructure
chemical_list: D000143:Acids