Effect of coloring and sintering on the translucency and biaxial strength of monolithic zirconia

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Statement of problem.The influences of coloring and sintering procedures on the optical and mechanical properties of monolithic zirconia have not been thoroughly investigated.Purpose.The purpose of this in vitro study was to investigate the effects of the coloring procedure and of varying final sintering temperatures on the translucency parameter (TP) and biaxial flexural strength (BFS) of monolithic zirconia.Material and methods.Disk-shaped specimens (N=210) of 2 different monolithic zirconia brands (Vita YZ HTWhite [VYZa]; Vita YZ HTColor A2 [VYZb]; Prettau Zirkonzahn [PZ]; Prettau Anterior Zirkonzahn [PZA]) with a diameter of 15 mm and a thickness of 1.0 ±0.05 mm were prepared. Half of the specimens prepared from noncolored blocks (VYZa, PZ, and PZA) received coloring liquid application. Then, the specimens were divided into 3 subgroups (n=10) according to the final sintering temperatures (1350°C, 1450°C, and 1600°C). The TP was determined by using a reflection spectrophotometer, and the BFS was tested with the piston-on-3-ball method in a universal testing machine. Data were statistically analyzed by multivariate multiple regression and Bonferroni tests (α=.05).Results.Significant differences were obtained among the groups based on the results of the TP and BFS (P<.05). The TP was affected by the changes in final sintering temperature. The varying final sintering temperatures demonstrated no significant effect on the BFS, except in group PZ (noncolored) that produced lower BFS when sintered at 1350°C than the subgroups sintered at 1450°C and 1600°C (P<.05). Coloring liquid application significantly decreased the TP of VYZa (sintered at 1350°C) but produced no significant effect on the groups PZ and PZA. Additionally, the coloring procedure had no significant effect on the BFS of tested materials (VYZa, PZ, and PZA) (P>.05).Conclusions.Increased sintering temperature leads to increased translucency with minimal impact on the BFS. The coloring procedure should be considered at the time of material selection to avoid possible reduction in translucency.

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