Crystalline structure of human enamel irradiated with Er,Cr:YSGG laser

The Er,Cr:YSGG system is commonly employed in tissue removal, but recently it has also been clinically evaluated for caries prevention. The present work explains the clinical and pre-clinical observations on the basis of the crystallographic changes that this laser can produce in the dental enamel. The analyzed samples were obtained from sound human third molar teeth. The laser irradiation was conducted with a Er,Cr:YSGG laser with 12.5 mJ/pulse, 0.25 W, and 2.8 J/cm2. The laser device operates at a wavelength of 2.79 μm, and the pulse width duration is 140 μs, with a repetition rate of 20 Hz of spot size of 750 μm. The crystalline structure of the samples was evaluated by X-ray diffraction at a synchrotron beamline The X-ray beam was configured at a grazing angle, to maximize the surface diffraction signal and to better detect the possible new crystallographic phase produced after the laser irradiation. It was observed that the crystallographic structure tetracalcium phosphate (TetCP, JCPDF 25-1137) exhibits several peaks that match more precisely with the new experimental peaks of the irradiated enamel. The present results suggesting the coexistence of tetracalcium phosphate with hydroxyapatite in enamel irradiated with Er,Cr:YSGG laser and can be the answer to the clinical and pre-clinical observations reported in the literature.