Laser irradiation of bone: II. Healing response following treatment by CO2and Nd : YAC lasers

Background: Currently, the most commonly used lasers for dental procedures are the Nd:YAG and CO2. Studies comparing healing of osteotomy defects prep ared with rotary burs to those created by laser irradiation have reported c onflicting results. The purpose of this study was to evaluate and compare t he histologic healing of bone in rat tibial osteotomy defects created eithe r by a dental bur, CO2 laser with and without removal of the char layer, an d Nd:YAG laser with char layer removed and with and without use of an air/w ater surface cooling spray. Methods: Tibial osteotomy defects were created in 4 groups of 6 rats each u sing the following: 1) #6 round bur with simultaneous saline irrigation; 2) CO2 laser with char layer intact; 3) CO2 laser with char layer removed; 4) Nd:YAG laser with air/water surface cooling, and char layer intact; 5) Nd: YAG laser with air/water surface cooling, and char layer removed; and 6) Nd :YAG laser without air/water surface cooling, and char layer removed. Both laser types were used at energy densities typically utilized for oral soft tissue surgery. Results: Progressive healing from day 0 through day 21 post-treatment was o bserved in all treatment groups. However, compared to controls treated by r otary dental bur, those specimens treated by laser, regardless of laser typ e, energy density, or other parameters, exhibited a delay in healing that a ppeared to be related to the presence of residual char in the osseous defec t. Specimens treated with the Nd:YAG laser using an air/water surface coola nt exhibited a decreased thickness and continuity of the char layer and yie lded the only specimens with new bone formation at the surface of the laser ablation defect. In addition, the normal pattern of bone remodeling in the rat tibia appeared to have been altered by laser irradiation. Conclusions: In this animal model, laser-induced osteotomy defects, when co mpared to those prepared by rotary bur, exhibited a delayed healing respons e that appeared to be related to the presence of residual char in the osseo us defect.