October 16, 2021
Not all commercially available zirconia powders are the same. Differences between products in grain size and additives greatly control the zirconia block material’s strength, long-term stability, and translucency.
1. Furthermore, the varying processes by which dental zirconia powders are formed into milling zirconia blocks significantly influences the quality of the final product. Unidirectional axial pressing creates a milling zirconia block shape that is very precise but lacks material consistency and therefore is not ideal for larger restorations.
2. On the other hand, cold isostatic pressing (CIP) uses a liquid medium, like water, to apply pressure uniformly in all directions to the zirconia powder enclosed in a mold to maintain its shape
3. The very high pressures involved with CIP minimize and remove voids in the powder to increase material density and produce a green-state (unsintered) zirconia block with excellent homogeneity throughout the entire material. The green-state zirconia block is then pre-sintered to allow it to be easily milled and post-processed by the technician. The final production step involves sintering the zirconia at very high temperatures (1350°C to 1500°C) whereby the final restoration hardens and shrinks linearly by 20% to 25% to achieve the desired strength and optical properties.
The first generations of high-strength CIP zirconia milling materials resulted in monochromatic and densely opaque restorations that exhibited limited esthetics unless layered. However, over the past 5 years, newer iterations of zirconia block materials have evolved into milling zirconia blocks that are trending toward ever higher translucency and pre-shaded zirconia block or multilayer zirconia blocks that greatly increase the esthetic outcome while reducing production processes. A great benefit to these high-translucency materials is that they require less reduction than monolithic glass-ceramic restorations and are kinder to natural opposing dentition.
In the past year, new formulations of zirconia milling blocks have included those that can be sintered in as few as 2 hours. As the top three zirconia block manufacturer in china, Yucera’s zirconia block fully reach this requirement with above production process, which can be fast sintered in 2 hours for some urgent case, below 3 units zirconia crown. Preshaded zirconia block and multilayer zirconia block efficiently save dental technician’s time to dying colors, ideal for large-span restorations.