Traditional White Zirconia
In the past two decades, tetragonal zirconia (3 mol % Yttria stabilized Tetragonal Zirconia Polycrystals, 3Y-TZP) has gradually become the mainstream ceramic material for dental restoration due to its very good mechanical properties, especially with the development of computer aided design and computer aided manufacturing(CAD/CAM). The popularization and application of technology in oral restoration can digitally compensate the sintering shrinkage of zirconia, and the size of the restoration can be controlled more accurately, so that the all-ceramic restoration technology has gradually developed rapidly and is widely used in clinical practice, especially for the production of multi-unit full-scale posterior teeth. Restoration of the Porcelain Long Bridge. This zirconia all-ceramic restoration material is the first type of zirconia that restorers come into contact with. Because this zirconia ceramic is mostly chalky, it is called "white zirconia".
The white zirconia all-ceramic material uses 3 mol% (5.2 wt%) yttrium oxide (Y2O3) as a stabilizer, adds 0.25-0.5 wt% alumina as a flux, and the main crystal phase is tetragonal zirconia (3Y- TZP) with grain size ranging from 0.5 μm to 1.0 μm. In this multiphase polycrystalline ceramic structure, due to the large refractive index (2.20) of zirconia, which does not match the refractive index of the glass matrix (1.50), the size of the crystals is larger than the wavelength of the incident light, in addition to the non-cubic phase zirconia The crystal itself is a birefringent crystal, and the incident light is scattered at the grain boundaries, pores, additives, etc., so this traditional zirconia ceramic material has poor semi-transparency and high resistance to light. However, because the main crystal phase 3Y-TZP has the effect of phase transformation and toughening, the first-generation zirconia all-ceramic materials have high strength and high fracture toughness. The bending strength is generally as high as 1000~1500 MPa, and the fracture toughness is about 3.5~4.5 MPa .m1/2.
White zirconia is usually used as the coronal material for the restoration of full crowns or all-ceramic bridges, and combined with sintered surface veneer porcelain to obtain better aesthetic effects, it can be used for the restoration of single crowns and fixed bridges of anterior and posterior teeth. The matching and combination of crown and veneer porcelain has the risk of porcelain chipping, and the incidence of porcelain chipping is even higher than that of porcelain-fused-to-metal full crown restorations. At present, this kind of white zirconia has gradually withdrawn from the market.
Representative products of the first generation of zirconia ceramics include Lava Frame (3M ESPE), KaVo Everest ZH (KaVo Dental), Vita YZT (Vita Zahnfabrik), Zenostar MO (Wieland Dental), etc.