[Evaluation of alumina effects on the mechanical property and translucency of nano-zirconia all-ceramics].

Objective: To study the effects of alumina content on sintered density, mechanical property and translucency of zirconia nanocomposite all-ceramics.

Methods: Specimens of zirconia nanocomposite all-ceramics were divided into five groups based on their alumina content which are 0% (control group), 2.5%, 5.0%, 7.5% and 10.0% respectively. The sintered densities were measured using Archimedes' method. Specimens' bending strengths were measured with three-point bending test (ISO 6872). The visible light transmittances were measured with spectrophotometric arrangements and the fractured surfaces were observed using scanning electron microscope (SEM).

Results: The control group of pure zirconia could be sintered to the theoretical density under pressure-less sintering condition. The bending strength was (1100.27 ± 54.82) MPa, the fracture toughness was (4.96 ± 0.35) MPa×m(1/2) and the transmittance could reach 17.03%. The sintered density and transmittance decreased as alumina content increased from 2.5% to 10%. However, the fracture toughness only increased slightly. In all four alumina groups, the additions of alumina had no significant effect on samples' bending strengths (P > 0.05). When the content of alumina was 10%, fracture toughness of specimens reached (6.13 ± 0.44) MPa×m(1/2) while samples' transmittance declined to 6.21%. SEM results showed that alumina particles had no significant effect on the grain size and distribution of tetragonal zirconia polycrystals.

Conclusions: Additions of alumina to yttria-tetragonal zirconia polycrystals could influence its mechanical property and translucency. Additions of the other phase to zirconia ceramics should meet the clinical demands of strength and esthetics.