Study On Optical Properties Of Submicron ZrO₂ Toughened Al₂O₃ Dental Ceramic

Objective The aim of this paper was to investigate the influences of composite additive content, sintering temperature and zirconia content on translucency of dental zirconia toughened alumina ceramic, to study the relationship between the microstructure of specimens and the translucency, and to find out the way by which the specimens are more translucent. Then, we can use these parameters to further study the optical property of the material and its application.Methods Dental zirconia toughened alumina ceramics were fabricated by centrifugal infiltration casting method and sintered in atmosphere. Sample reflectance was measured with an apparatus which can measure reflectivity; Microstructure of specimens was observed with a scanning electron microscope; Crystallite phase composition was measured by X-ray diffraction; Mechanical properties were measured at the same time. Optical constants were calculated by the Kubelka-Munk theory.Resultsâ‘ The specimens without composite additive were less translucent than the specimens codoped with 1%, 2% composite additive. The contrast ratio (CR) of the specimens codoped with 1% composite additive content was 0.868, the specimens codoped with 1% composite additive content had the highest translucent degree. However, the CR was increased and the specimens became less translucent with the increasing of composite additive amounts.â‘¡Sintering temperature had effects on the translucency to a degree. The translucency increased with the increasing of sintering temperature. The specimens were most translucent when sintered at 1550°C, the CR of these specimens was 0.896.â‘¢The amounts of the pores increased with the increasing of the content of zirconia. There were a lot of pores in the specimens with 50% zirconia. The specimens with 10% zirconia were more translucent, the CR of these specimens was 0.938.â‘£For the optimized ZTA ceramic, the scattering coefficient was 6.478±0.34mm^-1, the absorption coefficient was 0.009±0.003mm^-1, the infinite optical thickness was 6.424±1.433mm, the transmission was from 3.98% to 4.64%.Conclusions (1) Composite additives (TiO₂, SiO₂, La₂O₃, MgO) were necessary for improving the translucency of the dental zirconia toughened alumina ceramics. Small amounts of composite additives could inhibit the grain growth, and reduced the porosity, thus, increased the translucency of the specimens. But the porosity increased, relative density decreased and a new phase formed with the increasing of composite additives content, finally, the translucency of the specimens decreased.(2) Sintering temperature will produce large effects on the translucency. With increasing sintering temperature, the amounts of pores decreased, the grain size increased and turned into uniform, the arrangement of the grains changed to be more regular. The process reduced the effects of light scatter, refraction and reflectance, and therefore increased the translucency of the specimens.(3) Different refractive index existed between alumina and zirconia made the translucence of the specimens low. Pores and light loss caused by different refractive index increased with the increasing of zirconia content, so the specimens became much less translucent.(4) Optical constants of the optimized ZTA ceramic obtained from this study were in the same order of magnitude compared with the results by other researcher's. These constants can be used for further study on optical properties of submicron ZrO₂ toughened Al₂O₃ dental ceramic.