牙科氧化锆陶瓷的低温时效性能研究

目的 研究时效对5种牙科氧化锆陶瓷结构稳定性的影响.方法 5种氧化锆预烧结块(A组:TZ-3YS;B组:Vita In-Ceram YZ;C组:Ivoclar;D组:Cercon Smart;E组:Kavo)各切取15 mm×15 mm×1.5 mm氧化锆试件18片,常压致密烧结.时效处理如下:置于高温高压消毒炉中进行循环热处理,条件是134℃,0.2 MPa压力,维持时间为0h、1h、2h、3h、4 h、5h.X射线衍射分析(X-ray diffraction,XRD)试件的晶相结构,计算试件表面单斜相(m相)的相对含量.原子力显微镜观察A组和D组时效1、4 h的抛光试件.A组氧化锆再制备25 mm×4 mm×1.2 mm的试件30根,均分为未退火组(时效前)、退火组(时效前)和时效组(时效后),测试试件的三点弯曲强度.结果 除D组试件外,A、B、C、E组试件的m相含量均随时效时间的延长而增加,A组试件的m相含量最高,E组次之,B组和C组相近.XRD未检测到D组试件表面有m相,但使用原子力显微镜可观察到D组试件有m相晶核的成核和生长.时效前后A组试件的三点弯曲强度未衰减,未退火组试件三点弯曲强度(1301±169)MPa]显著高于退火组(1120±185)MPa]和时效组(1158±111)MPa],差异有统计学意义(P＜0.05);而退火组与时效组间差异无统计学意义(P＞0.05).结论 牙科氧化锆陶瓷的低温时效效应具有时间依赖性,但时效效应并未使TZ-3YS的三点弯曲强度降低.

In vitro evaluation of low-temperature aging effects of Y2O3 stabilized tetragonal zirconia polycrystals dental ceramics

OBJECTIVE: To investigate the influence of in vitro low-temperature degradation (LTD) treatment on the structural stability of 5 kinds of Y2O3 stabilized tetragonal zirconia polycrystals (Y-TZP) dental ceramics. METHODS: TZ-3YS powder was compacted at 200 MPa using cold isostatic pressure and pre-sintered at 1050 degrees C for 2 h forming presintered blocks. Specimens were sectioned into 15 mm x 15 mm x 1.5 mm slices from blocks of TZ-3YS, Vita In-Ceram YZ, Ivoclar, Cercon Smart, and Kavo Y-TZP presintered blocks, 18 slices for each brand, and then densely sintered. Specimens were divided into 6 groups and subjected to an accelerated aging test carried out in an autoclave in steam at 134 degrees C, 0.2 MPa, for 0, 1, 2, 3, 4, and 5 h. X-ray diffraction (XRD) was used to identify crystal phases and relative content of monoclinic phase was calculated. Specimens for three-point bending test were fabricated using TZ-3YS ceramics according to the ISO 6872 standard and bending strength was tested before and after aging. The polished and aging specimens of TZ-3YS and Cercon Smart zirconia ceramics were observed by atomic force microscopy (AFM) to evaluate surface microstructure. RESULTS: Tetragonal-to-monoclinic phase transformation was detected for specimens of TZ-3YS, Vita In-Ceram YZ, Ivoclar, and Kavo zirconia ceramics except for Cercon Smart ceramics after aging, and the relative content of monoclinic phase was increasing with the prolonged aging time. TZ-3YS was the most affected material, Kavo took the second, and Vita and Ivoclar were similar. Aging had no significant negative effects on flexural strength of TZ-3YS with average bending strength being over 1100 MPa. The nucleation and growth of monoclinic phase were detected by AFM in surface of Cercon Smart zirconia in which monoclinic phase was not detected by XRD. CONCLUSIONS: The results suggest that LTD of dental Y-TZP is time dependent, but the aging test does not reduce the flexural strength of TZ-3YS. The long-term clinical serviceability of dental Y-TZP needs further observation.