Morphological and Atomic Analytical Changes after CO 2 Laser Irradiation Emitted at 9.3 μm on Human Dental Hard Tissues

Objective: The purposes of this study were to examine the effects of CO₂ laser emitted at 9.3 μm on human sound and carious dental hard tissue ablation with a stereoscope, scanning electron microscope (SEM), and energy dispersive X-ray spectrometer (SEM-EDX) and to identify possible applications of this laser in clinical treatment. Summary Background Data: There has been no report of morphological changes or atomic analytical studies on carious hard tissues after laser irradiation with 9.3 μm CO₂ laser. Methods: Sixty extracted human teeth with no caries and sixty teeth with enamel or dentin caries were used for this study. All teeth were horizontally sectioned into slices (approximately 3 mm in thickness) and the samples were irradiated with CO₂ laser using the following two parameters: a fluence of 78 J/cm² and 5 pps or 20 pps for 2 sec. After laser irradiation, half of the samples were observed by stereoscopy and SEM and the other half were analyzed by SEM-EDX. Results: The lased sound enamel and dentin surfaces showed crater-like structures which had been produced by the high laser energy. On the other hand, some portions of carious hard tissues were evaported by the laser. A slight amount of carbonization was observed by stereoscopy. Calcium (Ca) and phosphorus (P) content of sound or carious hard tissues was increased significantly (p < 0.01) after laser irradiation, but the ratio of Ca to P after laser irradiation was significantly increased (p < 0.01) on sound hard tissue only. Conclusion: These results suggest that the 9.3 μm CO₂ laser may be useful for the prevention or removal of caries in clinical situations.