Effect of coloring with various metal oxides on the microstructure, color, and flexural strength of 3Y-TZP

The purpose of this study was to investigate the effect of cerium and bismuth coloring salts solutions on the microstructure, color, flexural strength, and aging resistance of tetragonal zirconia for dental applications (3Y-TZP). Cylindrical blanks were sectioned into disks (2-mm thick, 25-mm in diameter) and colored by immersion in cerium acetate (CA), cerium chloride (CC), or bismuth chloride (BC) solutions at 1, 5, or 10 wt %. The density, elastic constants, and biaxial flexural strength were determined after sintering at 1350 degrees C. The crystalline phases were analyzed by X-ray diffraction before and after aging in autoclave for 10 h. The results showed that the mean density of the colored groups was comparable with that of the control group (6.072 +/- 0.008 g/cm(3)). XRD confirmed the presence of tetragonal zirconia with a slight increase in lattice parameters for the colored groups. A perceptible color difference was obtained for all groups (DeltaE* = 2.57 +/- 0.48 to 14.22 +/- 0.98), compared with the control. The mean grain size increased significantly for the groups colored with CC or CA at 10 wt %, compared with the control group (0.318 +/- 0.029 mm). The mean biaxial strength of CA1%, CA5%, and BC1% groups was not significantly different from that of the control group (1087.5 +/- 173.3 MPa). The flexural strength of all other groups decreased linearly with increasing concentration for both cerium salts (860.7 +/- 172 to 274.4 +/- 67.3 MPa). The resistance to low temperature degradation was not affected by the coloring process. Coloring with cerium or bismuth salts produced perceptible color differences even at the lowest concentrations. A decrease in flexural strength at the higher concentrations was attributed to an increase in open porosity.