Basic study of morphological changes and surface roughness of cavities prepared by TEA CO2 laser irradiation. 
The purpose of this study was to investigate the morphological change of dental hard tissue and surface roughness of cavities prepared by transversely excited, atmospheric pressure (TEA) CO2 laser irradiation.  It has been reported that dental hard tissues and bone can be removed by a long-pulse of TEA CO2 laser irradiation with minimal thermal damage.  However, there are few reports on the surface roughness of lased teeth.  The TEA CO2 laser was irradiated on the enamel and dentin surfaces of extracted human teeth under the following conditions: wavelength, 10.6 microm; output, 95 mJ/pulse; pulse repetition rate, 1 Hz; irradiation time, 7.5 microsec/shot; and energy density, 7.9 J/cm2.  Morphological studies were performed by histological and scanning electron microscopic (SEM) examination.  Surface roughness of prepared cavities was measured by three-dimensional laser microscopy.  Irradiated dentin produced a deeper defect (705 +/- 11 microm) than the enamel (501 +/- 10 microm).  Histological appearance showed a basophilic line at the margin of lased dentin.  SEM observation noted that the surfaces of the enamel cavity seem to be melted, and dentinal tubules were sealed.  The surface roughness of the enamel cavity wall and dentin floor were 175 +/- 5 microm and 170 +/- 6 microm, respectively.  These findings suggest that it is possible to remove carious dental hard tissue or cavity preparation with the TEA CO2 laser irradiation.  Lased dental hard tissue can facilitate caries prevention, and surface roughness of the cavities might improve the bond strength of restorative dental materials.