Synthesis and Characterization of 85-15% Zirconia-Toughened-Alumina Composites for CAD/CAM Prostheses

Objectives: Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is widely used in prosthodontics, but shows hydrothermal instability at low temperatures due to transformation from the metastable tetragonal phase to the monoclinic phase. This study aimed to synthesize and characterize a polycrystalline composite with 85% of alumina reinforced with 15% of conventional zirconia (ZTA: zirconia-toughened-alumina) suitable for multi-unit prostheses.
Methods: Disc-shaped specimens (1mm-thick x 1.2mm in diameter) were fabricated by uniaxial followed by isostatic pressing of ceramic powders. After sintering, polishing of both sides was performed with diamond disks and suspensions up to 1μm. The optical characterization was performed by means of reflectance on a white and a black background to determine the contrast ratio (CR) and the translucency parameter (TP) of the experimental groups. XRD and SEM analyses were performed to evaluate the crystalline structure (n=10). Biaxial flexural strength (ISO 6872:2015) and fractography were also performed (n=30) with strength data evaluated by Weibull analysis.
Results: Optical properties evaluation showed CR-1.00 and TP of 1.72 (S.d. 0.44). XRD showed evidence of both Al₂O₃ and ZrO₂ phases well mixed. SEM depicted an homogeneous surface in most samples. The characteristic strength was 881.68MPa (837.94-927.71) and Weibull modulus was 8.75 (6.19-12.38).
Conclusions: A ZTA composite was developed and according to the characterization performed, it could be used as substructure framework for 4-unit porcelain-veneered prostheses (strength ≥ 800MPa). The low TP value indicated that this material is suitable to hide dark substrates.