Ideal Condition of Nd:YAG Laser Irradiation for Pain Control

Abstract

Purpose We have reported the efficacy of Nd:YAG laser irradiation for pain control in dental or periodontal treatments. However, there are few reports on the fundamental mechanisms of the effect of this laser on the sensory nervous systems. In this study, we investigated some factors which influenced the suppressive effect on the conduction of action potentials, in order to obtain data for producing a guide book for Nd:YAG laser irradiation in dental clinical treatment. Materials and Methods African clawed frog (Xenopus laevis) was immobilized with ice water and the spinal cord was destroyed. Dorsal surface skin together with three pairs of tactile nerve fine bundles (6 fine bundles in total) was removed, and cut into three pieces each with two tactile nerve bundles. Each piece of skin was put on filter paper soaked with physiological buffer solution, and was fixed on a rubber mat with metal pins. Chinese ink was painted on the dissected fine nerve bundle. Tactile stimulus was given with a single fiber of hemp palm at a tactile pressure 1-2 gf. Under audio visual monitoring, action potentials to the tactile stimulus were recorded by a silver electrode, and counted by a spike counter. Finally, rates of the action potential responses were recorded by a pen recorder. After Nd:YAG laser irradiation with various durations or pulse energies, tactile responses were periodically recorded, taking care to stimulate the same surface area under a dissection microscope. Results The suppression of action potentials depended upon the total energy rether than the pulse energy of the laser irradiation. The suppression was irreversible when the laser irradiation exceeded a certain total energy. Reversible suppression of action poten tials was obtained with sweeping mode irradiation, but it was very difficult to get this effect with fixed mode irradiation. This result endorses the propriety of the recommendation of the sweeping mode irradiation in dental treatment in our department. We think that these results would be useful for making a guideline for Nd:YAG laser irradiation in dental clinical treatment.