Morphological and Compositional Changes in Human Teeth following 9.6-um CO2 Laser Irradiation In Vitro

Nagai, Kaori / Kinoshita, Jun-Ichiro / Kimura, Yuichi / Matsumoto, Koukichi

Journal of Oral Laser Application 2006; 6: 265-276

Purpose: The purpose of this study was to examine the morphological and compositional changes in human teeth following 9.6-μm CO2 laser use for cavity preparation. Materials and Methods: Thirty-six extracted human teeth were randomly divided into two groups: a CO2 laserirradiated group and a turbine group. The 9.6-μm CO2 laser was used to irradiate 29 teeth for 20 s at 20 mJ pulse energy with 200 pps and 4 W output under water spray. Cavities in the turbine group were prepared using a diamond bur on 7 teeth. The morphology of samples was observed by stereomicroscopy, light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), or confocal laser scanning microscopy (CLSM). The calcium (Ca) and phosphorus (P) levels in each sample were measured by energy dispersive x-ray spectroscopy (SEM-EDX), and the results were analyzed statistically using the Mann-Whitney U-test. Results: The cavity walls of the laser-irradiated group were not clear but whitish and relatively smooth when observed under light microscopy, and had rough boundary lines and wavy surfaces when viewed with SEM. There was no damage immediately underneath the irradiated surfaces when viewed with TEM. Mineral analyses (Ca, P) showed no statistically significant difference in the composition of the enamel or dentin after using a bur, but significant differences in weight percentage of the P level were found after laser irradiation. Conclusion: It was demonstrated that 9.6-μm CO2 laser shows potential for clinical application in cavity preparation without harming surrounding dental hard tissues.