In this study, the wavelength of a CO₂ laser was modified to 9.45µn;m (Modi-CO₂ laser) and the cutting efficiency of Modi-CO₂ laser was evaluated. We used the freshly extracted human molars without carious regions. The dentin surface of the thawed teeth was polishing with alumina (0.05 mm). Modi-CO₂ laser was irradiated by TEA-CO₂ laser. Modi-CO₂ laser was irradiated on the polished dentin surface under the irradiation conditions of 1 MW/pulse and 1, 5, 10 and 50 pulses. The pulse width of one pulse was set to 100 ns. The Modi-CO₂ laser-irradiated dentin surfaces were Au-spattered and were observed by an electron surface roughness analyzer. The volume lost by the irradiation of the laser was calculated from the diameter and the depth of cavity. The relationship between the lost volume and the irradiation energy was statistically analyzed by one-way ANOVA and Scheffe's test (p<0.05). No measurable loss of dentin was detected with Modi-CO₂ laser-irradiation of 1 and 5 pulses. The lost volumes of dentin with 10 and 50 pulses were 143333 and 342333 mm³. The lost volume by the irradiation of Modi-CO₂ laser significantly increased with an increase of the pulse of Modi-CO₂ laser.