OBJECTIVES: To compare the effects of different sintering protocols on density, translucency, microstructure, crystallography, and biaxial flexural strength of different yttria concentrations of Tosoh zirconia materials (TZ-3YSB-E, TZ-3YB-E, Zpex, and Zpex Smile).
MATERIALS AND METHODS: A total of 242 zirconia discs were manufactured from commercially available Tosoh zirconia powders. Zpex smile, Zpex, TZ-3YB-E, and TZ-3YSB-E were uniaxially dry pressed into cylindrical blocks using a 5/8-inch internal diameter steel die set under a hydraulic press load of 3,000 N (Carver Press). Blocks were partially sintered at 1000 °C and sectioned into discs with a thickness of 2 mm x 15 mm by an IsoMet 5000 section machine. The discs were fully sintered using three protocols: 1) regular sintering using Vita Zyrcomat T furnace at 1520 °C for 2 h (total cycle time of 7 h); 2) fast sintering using Sirona inFire HTC SPEED at 1540 °C for 30 min (total cycle time of ~1.5 h). 3) speed sintering using Sirona CEREC Speed Fire furnace at 1579 °C for 5 min (total cycle time of ~18 min). After sintering, the translucency was characterized by contrast ratio using a spectrophotometer (X-Rite Ci7600). The specimens were then subjected to one of the following post treatments: 1) no treatment (control), 2) low temperature degradation (LDT) using 120 °C steam for 1 day (LDT 1d), 3) low temperature degradation for 1 week (LDT 1wk), 4) cyclic loading fatigue for 50,000 cycles, and 5) cyclic loading fatigue for 100,000 cycles.
The microstructure of the materials was characterized using a scanning electron microscope (SEM), and the crystal grain size was measured using NIH ImageJ. A ball-on-three-balls biaxial flexural strength was performed at a crosshead speed of 0.5 mm/min using an Instron 5566A. The crystallographic phases of Tosoh zirconia were evaluated by X-ray diffraction (XRD) utilizing a D2 Phaser desktop diffractometer and the phase fraction was determined by full-profile refinements using GSAS-II software. The statistics were analyzed using JMP Pro 15.0 for comparing translucency, flexural strength, and grain size of all specimens. Statistical significance was assigned to p-values less than 0.05.
RESULTS: There was a significant difference in the density of zirconia powders, with Zpex Smile powder having the lowest density of 5.81g/cm3, whereas Zpex powder had the highest density of 5.93 g/cm3. Mean grain size for speed sintering Zpex Smile was significantly larger than fast and regular sintering protocols. Grain size of TZ-3YSBE for regular sintering was significantly larger than that of speed and fast sintering. Speed sintered zirconia showed a significantly higher contrast ratio than other sintering protocols. Fast sintering groups had significantly higher contrast ratios than regular sintering for Zpex and Zpex Smile. For regular and fast sintering, TZ-3YBE had the highest contrast ratio, and Zpex Smile had the lowest value. Overall, speed sintering resulted in the highest contrast ratio and regular sintering the lowest ratio. There was a statistically significant effect on crystal phases resulting from the zirconia powders and post sintering treatments. The results also indicated that Zpex Smile had a combination of cubic and tetragonal phases with a higher percentage of the cubic phase than other zirconia types. Speed sintered zirconia had significantly lower biaxial flexural strength values. However, there was no significant difference in biaxial flexural strength of TZ-3YB-E for different sintering protocols and post treatments.
CONCLUSION: The sintering protocols significantly impacted zirconia grain size, crystallography, and biaxial flexural strength. Speed sintering provided lower translucency and flexural strength.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/42847 |
| Date | 05 August 2021 |
| Creators | EL Azzouni, Dania Hany |
| Contributors | Giordano, Russell |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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