title: Morphological and atomic analytical changes after CO2 laser irradiation emitted at 9.3 microns on human dental hard tissues.
abstract: OBJECTIVE
  The purposes of this study were to examine the effects of CO2 laser emitted at 9.3 microns on human sound and carious dental hard tissue ablation with a stereoscope, scanning electron microscope (SEM), and energy dispersive X-ray spectrometer (SEM-EDX) and to identify possible applications of this laser in clinical treatment.
  
  
  BACKGROUND
  There has been no report of morphological changes or atomic analytical studies on carious hard tissues after laser irradiation with 9.3 microns CO2 laser.
  
  
  METHODS
  Sixty extracted human teeth with no caries and sixty teeth with enamel or dentin caries were used for this study. All teeth were horizontally sectioned into slices (approximately 3 mm in thickness) and the samples were irradiated with CO2 laser using the following two parameters: a fluence of 78 J/cm2 and 5 pps for 2 sec. After laser irradiation, half of the samples were observed by stereoscopy and SEM and the other half were analyzed by SEM-EDX.
  
  
  RESULTS
  The lased sound enamel and dentin surfaces showed crater-like structures which had been produced by the high laser energy. On the other hand, some portions of carious hard tissues were evaported by the laser. A slight amount of carbonization was observed by stereoscopy. Calcium (Ca) and phosphorus (P) content of sound or carious hard tissues was increased significantly (p < 0.01) after laser irradiation, but the ratio of Ca to P after laser irradiation was significantly increased (p < 0.01) on sound hard tissue only.
  
  
  CONCLUSIONS
  These results suggest that the 9.3 microns CO2 laser may be useful for the prevention or removal of caries in clinical situations.
authors.affiliation: Department of Endodontics, Showa University School of Dentistry, Tokyo, Japan. tkeiko@hp.dent.showa-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.forename: Y
authors.initials: Y
authors.lastname: Kimura
authors.forename: K
authors.initials: K
authors.lastname: Matsumoto
mesh_terms: D002118:Calcium / Q000032:analysis; D002245:Carbon Dioxide; D003731:Dental Caries / Q000517:prevention & control; D003743:Dental Enamel / Q000737:chemistry / Q000528:radiation effects*; D003804:Dentin / Q000737:chemistry / Q000528:radiation effects*; D006801:Humans; D007834:Lasers; D008855:Microscopy, Electron, Scanning; D010758:Phosphorus / Q000032:analysis; D016369:Smear Layer; D013052:Spectrometry, X-Ray Emission; D018709:Statistics, Nonparametric
chemical_list: D002245:Carbon Dioxide; D010758:Phosphorus; D002118:Calcium