Caries prevention and Restoration by Ceramics Coating on Enamel Surface Using a CO_2 Laser

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To study new restoration and to improve the acid resistance of teeth, the enamel surface was coated with several ceramic materials by a carbon dioxide gas laser. The ceramic powder suspension were applied on the enamel surface treated with 37% phosphoric acid (K-etchant, Kuraray Co.), and then the enamel was irradiated by a pulsed CO_2 laser (Opelaser/03S, Yoshida Co.) at irradiation intensities of 1.0 watt for 30 seconds with a beam size of 0.49mm at the focal point. And all surface except for the circle of 3mm diameter on the irradiated enamel surface was painted with nail varnish. The painted enamel sample was immersed in 10 ml of 0.1M-acetic acid/sodium acetate buffer solution at pH 4.0 for 30 minutes. The calcium ions released in the buffer solution from the enamel were measured by flame analysis.The acid resistance of the enamel treated with the phosphate calcium glass (PGC) was extremely improved, that of the enamel treated with silica-zirconium oxide was slightly improved, and that treated with the porcelain for metal-ceramics was not improved. The increase of the acid resistance of the enamel treated with PGC may be due to good wetting of PGC melted by laser irradiation to the enamel surface, as the composition of PGC was analogous to hard tooth tissue that was calcium phosphate.It is well known that the enamel treated with fluoride anion followed by lanthanum cation showed good acid resistance. Therefore, the enamel etched with the phosphoric acid was treated with 1% sodium fluoride aqueous solution followed by 1% lanthanum chloride aqueous solution, and then was irradiated by the laser. However, the acid resistance of the irradiated enamel was not improved.