The Effect of the Rat's Mandibula by ArF Excimer Laser Irradiation

CO2 and Nd: YAG lasers are usually used in the clinical field. Since it is generally known that infrared lasers has thermal side effect, which cause damage to the soft and hard tissues. With infrared lasers, thermal energy densities high enough to remove the soft and hard tissues lead to structural changes, which can be seen as cracks, necrotic zone and carbonization. Recently, it has been demonstrated that the soft and hard tissue can be removed without thermal damage by excimer laser irradiation. However, there are a few studies about the effects of the ArF excimer laser on the bone tissue. The purpose of this study was to investigate the changes of the bone structure by ArF excimer laser irradiation.ArF excimer laser was irradiated on the surface of the rat's mandibula under the follow ing irradiation conditions; wave length; 193nm, output; 0.12W, pulse repetition rate;10HZ, spot size; 1.0×3.3mm, irradiation time; 60 and 120 seconds. By using the extirpated mandibula, we examined the thermal change on the surface of the non-vital mandibula dur ing laser irradiation by thermography system. The temperature rise was 34°C after 60 sec onds and 45°C after 120 scconds. Histological and scanning electron microscopical studies were perfomed immediately after the irradiation. The ArF excimer laser beam produced de fect with clean-cut margins in both non-vital and vital mandibula. There was very minimal evidence of thermal damage on the surrounding tissue. The bottom of the defect revealed sawtooth appearance on histological sections and cone or clavate appearance when examined with a scanning electron microscope. These findings suggested that it is possible to remove the bone tissue without thermal changes by ArF excimer laser irradiation. The effectiveness of this laser can be attributed to the photoablation of the bone tissue. The mechanism of the ArF excimer laser in this study has not been clarified yet. Therefore more research is necessary before this newtype of ultraviolet laser may be used in the clinical field in the future.