Increasing demands for high esthetics have led in an evolution in all-ceramic restorations. Typically, zirconia is widely used as blanks in CAD/CAM dentistry. In recent years, many studies have been reported to improve the transparency of zirconia, however, it''s non-cubic crystal structure limit to remain translucent materials.
The fabrication of transparent spinel using LiF as a sintering aid by hot pressing process was investigated in this study. Spinel is widely regarded as one of the most promising optical ceramics and already used in dentistry for decades. Spinel was completely mixed using ultrasonic probe with 0.1~0.3 wt% LiF by wet process with distilled water and ethanol. Then centrifuged and removed the supernantant. After drying overnight subsequent rolling, hot pressed at 1450℃ for 1 hr under pressure of 25~45 MPa using graphite die set.
Particle size distribution of spinel powder was analyzed with a laser diffraction. Density of the hot pressed samples was determined by Archimedes'' principle. Biaxial flexural strength of the hot pressed samples was measured using universal testing machine.
Density and strength of the hot pressed samples were decreased with increasing LiF content, while increased with increasing loading of hot pressing. All densities showed higher than 96% of the theoretical density(3.58 g/cm3). The maxima value of density and strength in this study were obtained when hot pressed at 1450℃ for 1 hr under pressure of 45 MPa with 0.1 wt% LiF, namely (3.57±0.02) g/cm3 and (297±37) MPa. The enhancing strength is expected if applying improved hot pressing method such as pulsed or isostatic.
Remarkable transmittant(86.8%), that is very close to the theoretical value(87%), sample successfully obtained when hot pressed at 1450℃ for 1 hr under pressure of 45 MPa with 0.2 wt% LiF and subsequent polishing.
Following research on the clinical application of the transparent spinel in esthetic dentistry is highly recommended hereafter.