Abstract : The purpose of this study was to evaluate the morphological change in root canal dentin and the suitability of carbon dioxide (CO₂) laser irradiation for root canal obturation. Two pulse modes, pulse mode (40 pps) and super pulse mode (151 pps) were used. Under 4 W laser power, the CO₂ laser was set to have a total energy of 32 J. The morphological changes in the root canal dentin were observed by using a scanning electron microscope. The effects on the apical sealing ability were examined by measuring the penetration distance of the dye.

 The following results were obtained :

 1. When the apical portion of the root canal was irradiated in either mode, no dentin loss or micro-cracks were found on the root canal dentin surfaces ; however, small globular structures and a wavy surface caused by the melting of dentin debris were found.

 2. As to the rate and distance of dye penetration from the apex, there was no statistically significant difference between the control (no laser irradiation) group and either mode group.

 3. Regarding the rate of extrusion of the root canal filling material from the apical foramen, there was no statistically significant difference between the control group and either irradiation mode group.