Improvement of Acid Resistance of Oral Hard Tissue Coated with Ceramic Materials by Using a Carbon Dioxide Laser

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The acid resistance of the enamel treated with PGC was extremely improved, that of the enamel treated with silica-zirconium oxide was slightly improved, and that treated with NORI 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.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 carbon dioxide gas laser used was Opelaser/03S (Yoshida Co.), the irradiation chip of the laser was hold at 20 mm high on the enamel surface. Those ceramics were the phosphate calcium glass (PGC, Asahi glass Co.), the porcelain for metal-ceramics (NORI, Noritake Co.), commercial silica-zirconium oxide. The ceramics were grinded followed by sieved with 400 mesh sieve, and the obtained powders w … More ere suspended with distilled water to 50 mg/ml. The ceramic powder suspension were applied on the enamel surface treated with 37% phosphoric acid (K-etchant, Kuratay Co.), and then the enamel was irradiated by a pulsed CO_2 laser at irradiation intensities of 1.0 watt for 30 seconds with a beam size of 0.49 mm at the focal point. And all surface except for the circle of 3 mm 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.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.On the other hand, to improve the operations of radiation and to reduce the damage of the enamel by laser irradiation, the laser with a wide focal point was studied. It was found that the enamel treated with PGC by using the laser with the wide focal point showed good acid resistance without the damage of the enamel. Less