Thermal oxidation effect on porcelain-titanium restoration.

Titanium has good corrosion resistance, light density, high strength and excellent biocompatibility. Conventional ceramicmetal restorations were used extensively in dentistry because of their esthetic appearance and good strength properties. The purpose of this study was to investigate the influence of various thermal treatments on the bond strength and physical properties of the porcelain-titanium system. Pure titanium was treated in a porcelain furnace at temperatures ranging from 600 to 1000 degrees C, under vacuum and in air, respectively. X-ray diffraction analysis revealed that the relative peak intensity of alpha-Ti was decreased, while the TiO2 was increased when raising the firing temperature. The vickers hardness number was increased at elevated temperatures, especially over 900 degrees C, and firing in air was harder than under vacuum. The tension-shear bond strength was highest in the green stage and lowest in the 1000 degrees C treated group. The metallographic microscopic of the porcelaintitanium interface revealed a thick band-like zone in the 1000 degrees C treated sample. Therefore it seems that the excess oxidation layer of TiO2 weakened the bond strength of porcelain-titanium. Contrary to the conventional ceramic-gold alloys system, the recommended degassing procedure was not suitable for the porcelain-titanium restoration.