Juntavee Niwut, Attashu Surawut
Department of Prosthodontics, Faculty of Dentistry, Khon Kaen University, Khon Kaen, Thailand.
Division of Biomaterials and Prosthodontics Research, Faculty of Dentistry, Khon Kaen University, Khon Kaen, Thailand.
J Clin Exp Dent. 2018 Aug 1;10(8):e821-e830. doi: 10.4317/jced.54749. eCollection 2018 Aug.
Sintering process is responsible for the strength of zirconia restoration. This study evaluated the effect of different sintering temperatures and sintered-holding times on flexural strength of translucency monolithic zirconia.
One hundred and thirty five zirconia bar specimens (width-length-thickness = 10×20×1.5 mm) were prepared from yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramic and randomly divided into nine groups to be sintered at different temperatures [decreasing- (SD, 1350°C), regular- (SR, 1450°C), and increasing- (SI, 1550°C) sintering temperature] and different sintered-holding times [shortening- (HS, 60 min), regular- (HR, 120 min), and prolonged- (HP, 180 min) sintered-holding time]. Flexural strength was determined using three-point bending test in a universal testing machine at 1 mm/min crosshead speed. An analysis of variance (ANOVA) and Tukey's multiple comparisons were used to determine for statistically significant difference of flexural strength (α=0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristics strength (σo) of the flexural strength. The crystal sizes were microscopically examined using scanning electron microscope (SEM). The phase composition of zirconia was determined using X-ray diffraction (XRD).
The mean±sd (MPa), m, and σo of flexural strength were 1080.25±217.19, 5.54, and 1167.53 for SDHS, 1243.41±233.17, 5.19, and 1352.30 for SDHR, 1298.92±235.68, 6.24, and 1394.79 for SDHP, 1303.34±171.87, 8.40, and 1377.90 for SRHS, 1331.73±278.84, 5.31, and 1444.50 for SRHR, 1348.13±283.35, 5.32, and 1460.68 for SRHP, 1458.45±289.19, 4.51, and 1604.41 for SIHS 1581.34±190.56, 8.20, and 1675.21 for SIHR and, 1604.10±139.52, 12.57, and 1667.90 for SIHP. The flexural strength was significantly affected by altering sintering temperatures and holding times (<0.05). Enlarging grain size and increasing t→m phase shifting related with raising temperatures and times.
Increasing sintering temperature and prolonged sintered-holding time lead to enhancing flexural strength of translucency monolithic zirconia, and are suggested for sintering process to achieve durable restoration. Flexural strength, monolithic zirconia, sintering temperature, sintered-holding time.
烧结过程决定了氧化锆修复体的强度。本研究评估了不同烧结温度和烧结保持时间对半透明整体式氧化锆弯曲强度的影响。
用钇稳定四方多晶氧化锆（Y-TZP）陶瓷制备135个氧化锆棒状试件（宽×长×厚 = 10×20×1.5 mm），随机分为9组，在不同温度[递减（SD，1350°C）、常规（SR，1450°C）和递增（SI，1550°C）烧结温度]和不同烧结保持时间[缩短（HS，60分钟）、常规（HR，120分钟）和延长（HP，180分钟）烧结保持时间]下进行烧结。在万能试验机上以1 mm/min的横梁速度通过三点弯曲试验测定弯曲强度。采用方差分析（ANOVA）和Tukey多重比较来确定弯曲强度的统计学显著差异（α = 0.05）。应用威布尔分析来确定弯曲强度的生存概率、威布尔模量（m）和特征强度（σo）。使用扫描电子显微镜（SEM）对晶体尺寸进行微观检查。使用X射线衍射（XRD）确定氧化锆的相组成。
SDHS组弯曲强度的平均值±标准差（MPa）、m和σo分别为1080.25±217.19、5.54和1167.53；SDHR组为1243.41±233.17、5.19和1352.30；SDHP组为1298.92±235.68、6.24和1394.79；SRHS组为1303.34±171.87、8.40和1377.90；SRHR组为1331.73±278.84、5.31和1444.50；SRHP组为1348.13±283.35、5.32和1460.68；SIHS组为1458.45±289.19、4.51和1604.41；SIHR组为1581.34±190.56、8.20和1675.21；SIHP组为1604.10±139.52、12.57和1667.90。烧结温度和保持时间的改变对弯曲强度有显著影响（<0.05）。晶粒尺寸增大以及t→m相转变增加与温度和时间升高有关。
提高烧结温度和延长烧结保持时间可提高半透明整体式氧化锆的弯曲强度，建议在烧结过程中采用以实现持久修复。弯曲强度、整体式氧化锆、烧结温度、烧结保持时间。
