High Permeability Zirconia Ceramics
Under the circumstance that the strength of the first and second generation zirconia has met the clinical needs, further improving the light transmittance of zirconia ceramics has become an urgent clinical need. Cubic zirconia can significantly improve the semi-permeability of zirconia materials and improve its optical properties. Therefore, more stabilizer yttria is added to the third-generation zirconia ceramics, so that in the final sintered full zirconia materials The content of cubic zirconia grains increases; on the other hand, the content of tetragonal zirconia decreases, and the stress-induced transformation toughening mechanism is weakened, so the strength and toughness of the material decrease significantly. This type of zirconia has a dual-phase microstructure composed of tetragonal zirconia and cubic zirconia crystals, and belongs to partially stabilized zirconia. Compared with the first-generation and second-generation zirconia all-ceramic materials, the light transmittance of the third-generation zirconia has been greatly improved, so the third-generation zirconia is also called "high-transmittance zirconia".
This type of high-transmittance zirconia all-ceramic material launched in 2017 uses 4 mol % yttria as a stabilizer (4Y-TZP), and the addition of alumina is less than 0.05 wt %, or almost no addition, cubic zirconia crystals The content of zirconia is greater than 25%, or even greater than 50%, and the other main crystal phases are mainly tetragonal zirconia, and the semi-permeability of the material is significantly improved, reaching high permeability (studies have shown that the TP value of high-permeability zirconia specimens with a thickness of 1.0mm is reaching about 30), but at the same time the mechanical properties are significantly reduced, the bending strength is 500~800MPa, and the fracture toughness is about 2.2~3.5 MPa.m1/2.
The third-generation zirconia all-ceramic material can be used for the restoration of anterior all-zirconia single crowns, bridges and anterior veneers due to its good optical properties, but the latest research shows that this type of zirconia fails to be used in the anterior area within 5 years The use of some minimally invasive restorations such as veneers, inlays, and onlays needs to be clinically evaluated, so further research is needed on the widespread use of such materials.