The effect of staining on the fully stabilized zirconia

• Main Authors: Fei-Ya Cheng, 鄭妃雅
• Other Authors: Shyh-Yuan Lee
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/wdvh7h

碩士 === 國立陽明大學 === 牙醫學系 === 105 === Fully stabilized zirconia (FSZ) has recently become an attractive dental material because of its superior biocompatibility, adequate mechanical properties and higher translucency than yttria stabilized tetragonal zirconia polycrystals (Y-TZP). However, FSZ crowns custom milled from the single-color zirconia block is unable to mimic natural tooth appearance. Consequently, zirconia crowns should be stained to achieve a more natural and favorable color match. Staining liquids mainly contained various metal oxides which might interfere with the microstructure of zirconia during final sintering and thus affect the mechanical and optical properties of FSZ. This study aimed to evaluate the effect of staining on flexural strength and translucency of FSZ. The elemental composition of different staining liquids was first determined by Energy Dispersive X-ray Spectrometer (EDX) and partially sintered FSZ blocks were cut into disc-shaped specimens using a CAD-CAM machine. The specimens were then randomly divided into nine groups (n = 8), in which eight experiment groups were stained with Vita shade A2, A4, B2, B4, C2, C4, D2, and D4 liquids, respectively, while specimens without staining were served as the control. All specimens were subjected to the final sintering and ended up with discs about 14 x 1 mm in size. Further, the microstructure, phase composition, density, bi-axial flexural strength and translucency of the sintered discs were measured and the data were statistically analyzed by one way ANOVA followed by post-hoc Tukey’s test (α = 0.05). EDX analyses showed various metal elements in different staining liquids. The major elements were alumina, iron, erbium, cobalt, calcium and chromium. Staining liquids of A2, A4, B2 and B4 mainly consisted of iron and erbium, while staining liquids of C2, C4, D2 and D4 mainly consisted of iron, in addition to other trace metal elements. The results indicated that the microstructure, bi-axial flexural strength and translucency of FSZ specimens were significantly influenced by staining treatments, where B2 and A4 groups revealed the highest density and the control group revealed the lowest; D2 group showed the largest grain size (1.31 ± 0.58 μm) and the control group showed the smallest (0.87 ± 0.44 μm); D2, C2 and A2 groups presented the highest bi-axial flexural strength and the control group presented the lowest; A4 and C4 groups revealed the lowest translucency and the control group revealed the highest. In summary, staining liquids consisted of different metal elements, but all of them contained iron. The stained FSZ revealed an increase in density, grain size and bi-axial flexural strength, but a decrease in translucency and indistinctive change in phase composition. Therefore, it is highly suspected that metal ions especially iron in staining liquids may assist FSZ sintering by rapid grain growth and void elimination, and thus increase its density and strength. Regarding the decrease in translucency of the stained FSZ, the light scattering effect of these metal ions could be accused, but it was still clinically applicable. In conclusion, stained FSZ has a great potential for restorations in the esthetic zone. Keywords：fully stabilized zirconia, yttria stabilized tetragonal zirconia polycrystals, staining, metal oxides, bi-axial flexural strength, translucency, contrast ratio