Particle-induced X-ray emission and scanning electron microscopic analyses of the effects of CO2 laser irradiation on dentinal structure

Objectives: The purpose of this study was to analyze the physico-chemical changes present on the dentinal surface after using CO2 laser irradiation, and to determine whether or not it is possible to seal the dentinal tubules. Methods: Thirty human-extracted first premolars were obtained for this study. A Class V cavity was prepared on the buccal surface of all the specimens with a carbide pear-shaped bur, using a conventional high speed handpiece. Fifteen premolars (experimental group) were irradiated with a CO2 laser (with a wavelength of 10.6 μm, 2 W, 10 J, 0.2 s, 25 pulses). The remaining 15 premolars were used as the control group. Results: Scanning electron microscopy showed that the effect of laser energy on dentin varied from charring, cratering, poring, fissuring, fracturing and cracking up to melting; also, the dentinal tubules were not sealed, in contrast with the control group in which the dentinal surfaces were more homogeneous. Particle-induced X-ray emission results showed that the irradiated dentinal surface presented a decrease in calcium content and an increase in phosphorous content, possibly due to a vaporization process which occurred during the irradiation. Conclusion: The physicochemical changes observed on the irradiated dentinal surface suggest that changes in the hydroxyapatite crystal structure take place, and that these structural changes may be responsible for the observed effects.