Conservation of inappropriate teeth to conserve was attempted with CO2 laser irradiation in our clinic. In two cases (female, 54 years old, right upper 1, and female, 39 years old, right upper 2), each tooth was diagnosed as inappropriate to conserve because of progressive internal resorption and apical periodontitis. After extraction of the teeth, the inappropriate portion of the tooth was cut and removed, surrounding tissue was removed and the root canals were filled. CO2 laser irradiation was made around the root of the tooth and inside the alveolus. The teeth were then re-implanted. After the surgery, laser irradiation on the gingiva was made periodically for several weeks. Successive observation (at 3, and 5.5 years, respectively) revealed that both teeth showed no special problem, such as loosening. It has been reported that low-power irradiation with CO2 laser promoted wound healing, multiplication of capillaries, and increased peripheral circulation. These effects of CO2 laser irradiation, reducing inflammation and increasing surrounding peripheral circulation, might result in the effective conservation of teeth. (C) 2002 Elsevier Science B.V. All rights reserved.