Chek Hai Lim
Lim, Chek Hai, Vardhaman, Sonaj, Reddy, Niyati, Zhang, Yu
University of Pennsylvania School of Dental Medicine, Department of Preventive and Restorative Sciences
Modern zirconia dental restorations are stabilized with various yttria contents and fabricated using different sintering protocols. This study aimed to elucidate the composition-process-properties relationship for various classes of zirconia, providing guidelines for fabricating zirconia restorations with desirable properties.Methods
Bisque-fired discs (Ø18 x 2 mm) were sintered at various temperatures with a 2-h dwell time at a heating/cooling rate of 5 °C/min. The as-sintered discs were characterized by X-ray diffraction for quantitative phase analysis using Rietveld Refinement. They were also utilized for the apparent density measurement using Archimedes’ principle. The sintered discs were then ground and polished to a 1-µm finish for grain size (thermally etched), translucency, and strength measurements.Results
A significant improvement of flexural strength was observed after 1300 °C for 3Y and 4Y zirconia, while that of 5Y zirconia increased after 1350 °C. The increase in strength was similar to the improvement of the apparent density of zirconia, where 3Y and 4Y zirconia achieved more than 99% dense after firing at temperatures above 1300 °C while 5Y zirconia attained the identical result at temperatures above 1350 °C. It indicated that the densification of zirconia occurred earlier with the lesser yttria content. Generally, translucency and grain size of the three zirconia materials ameliorated with increasing sintering temperatures and cubic contents, and reducing porosity. The optimum sintering temperature for the three zirconia compositions was 1500 °C when considering both translucency and strength properties.Conclusion
There is a lack of systematic studies on various zirconia compositions (3Y, 4Y, and 5Y) and their optimal use in clinical application as a monolithic restoration. Our findings show that while increasing yttria content in zirconia would delay the densification process, the temperature that gives the optimum clinical performance for both translucency and strength was 1500°C.