In this study, the enamel surface was irradiated using the Nd: YAG laser while the structural changes were observed using SEM imagery. The total amount of irradiation energy the output of the 200 J was distributed repeatedly at a speed of 10 pps, with the output set up only within the 100-900 mj range, at intervals of 100 mj and thus divided into 9 stages. The changes in each stage wer e examined and compared. With the results as follows:
1. When the Nd: YAG laser output is low, the formation of crater-like depressions with a structure resembling that of a lava flow after cooling tends to be minimal. On the other hand, a high output conspicuously brings about a degeneration of the smooth, linear and uniform tooth surface.
2. At every stage of irradiation output, the formation of reticulated fissures and small orifices was observed. No clear observation could be made, however with regard to differences in the number of formations or the effect of their size.