氧化锆陶瓷px--242A低温老化性能初步分析

目的：初步分析一种3摩尔钇稳定的纳米氧化锆陶瓷（Tz—Px一242A）的低温老化性能。方法：将烧结后的氧化锆试件随机分成4组,在高温高压灭菌锅里进行循环热处理,处理条件为在134℃、0．2MPa下,进行0h,1h,3h,5h不同时间的低温老化实验。测量低温老化实验前后的三点弯曲强度,并用XRD分析试件表面单斜相的比例。结果：随着低温老化时间的延长,试件表面单斜相含量增加,三点弯曲强度呈逐渐下降趋势。低温老化处理5h后强度仍高于1100MPa。结论：本实验用氧化锆陶瓷的低温老化性能具有时效依赖性,低温老化对三点弯曲强度无明显影响。：     

纳米SiO2溶胶对氧化锆基底与饰面瓷结合强度的影响

目的:探讨采用溶胶-凝胶技术在氧化锆表面制备薄纳米SiO2涂层对氧化锆基底与饰面瓷结合强度的影响,指导氧化锆全瓷冠的制作.方法:将软质氧化锆试件切割成15 mm×10 mm×2.5 mm大小的长方形瓷块40片,分为4组,每组10件,分别采用4种处理方式.A组-仅经1450℃结晶处理;B组-先经30％纳米SiO2溶胶渗透后,再经1450℃结晶处理;C组-先经1450℃结晶,然后用30％纳米SiO2溶胶渗透,再经1450℃热处理;D组-表面涂布纳米SiO2溶胶后,1450℃结晶处理;E组-镍铬合金烤瓷组,使用失蜡铸造法制作12 mm×8 mm×2 mm长方形镍铬合金条块10件.5组试件在其表面堆塑直径为5 mm、高4 mm的饰面瓷圆柱,然后进行剪切强度测试.采用SPSS 19.0软件包对数据进行统计学分析.结果:5组试件的剪切强度分别为A组(28.12±2.95) MPa、B组(31.09±3.94) MPa、C组(25.60±2.45) MPa、D组(31.75±4.90) MPa、E组(28.67±3.95) MPa.单因素方差分析显示5组间具有显著差异(P＜0.05),其中,C组与B组和D组均具有显著差异.结论:①溶胶-凝胶技术在结晶致密前氧化锆基底表面制备纳米SiO2涂层,能提高氧化锆基底与饰面瓷的结合强度;②在结晶致密的氧化锆基底表面制备纳米SiO2涂层,能降低氧化锆基底与饰面瓷的结合强度;③氧化锆与氧化锆专用饰面瓷的结合强度与常用金属与饰面瓷的结合强度一致;④通过溶胶-凝胶技术在结晶致密前的氧化锆基底表面导入SiO2溶胶,提高氧化锆与饰面瓷结合强度的技术路线切实可行.     

牙科热压铸造工艺对牙科低熔云母玻璃陶瓷显微结构的影响

目的:评价牙科热压铸造工艺对SiO2-K2O-B2O3-MgO-F系牙科低熔云母玻璃陶瓷的显微结构的影响.方法:原料粉在1 400℃熔融2 h制成玻璃柱和玻璃板,经切割分别制成柱状(12 mm×8 mm;n=48)和条形试件(20 mm×2 mm ×4 mm;n=48).柱状试件用于实验组的热压铸造,条形试件经历与实验组相同的热处理过程用于对照.通过差热分析(DTA)、X射线衍射分析(XRD)、扫描电子显微镜观测(SEM)及三点弯曲强度的测试,比较牙科热压铸造工艺对SiO2-K2O-B2O3-MgO-F系牙科低熔云母玻璃陶瓷的微观结构及抗弯强度的影响.结果:玻璃的核化温度为530℃,品化温度在600～800 ℃之间.热压铸组的晶体呈现一定程度的定向排列,而对照组的晶体随机交错分布.热压铸组的三点弯曲强度(142.08±9.39～177.94±7.44)MPa高于对照组的(118.44±12.04～147.16±4.59)MPa.热处理后主要晶体为云母,压铸后硅锌矿增加.结论:牙科热压铸造工艺可以在SiO2-K2O-B2O3-MgO-F系牙科低熔云母玻璃陶瓷内部形成各向异性的结构,从而有助于提高力学强度.     

牙科着色氧化锆陶瓷饰瓷前后的力学性能及断裂模式分析

目的:本研究对牙科氧化锆陶瓷着色及构筑饰面瓷前后的力学性能及断裂模式进行分析.方法:球磨混合一定组分的着色剂(氧化铁及氧化铈)和3Y-TZP(钇稳定氧化锆)粉体制备着色氧化锆陶瓷.根据ISO6872牙科陶瓷标准,制备着色和未着色氧化锆陶瓷的三点弯曲强度样品和构筑饰面瓷后的双层瓷样品,核心瓷与饰面瓷的厚度比为1:1.对所获得样品进行三点弯曲强度、断裂韧性和维氏硬度测试.采用X射线衍射(XRD)分析物相结构,扫描电镜(SEM)观察样品的断裂模式.结果:白色氧化锆陶瓷与着色氧化锆陶瓷的三点弯曲强度分别为1301 MPa和1203:MPa,统计学结果显示二者间没有明显差异,构筑饰面瓷后的三点弯曲强度分别为817 MPa和803 MPa,统计学结果显示二者间没有明显差异,但构筑饰面瓷后比单一材料样品强度降低,二者间有显著差异.在所有的双层瓷样品中,断裂模式的应力位移曲线显示为单峰断裂模式,断裂起始于核心瓷的张应力面中心区域同时发生饰面瓷的破碎和瓷层剥脱.结论:对氧化锆粉体的适当着色并没有明显影响材料的机械性能,着色和未着色氧化锆材料与饰面瓷具有良好的物理匹配性.     

牙科着色氧化钇稳定四方多晶氧化锆陶瓷的结构与性能

目的添加不同着色剂组合,配制着色的牙科氧化钇稳定四方多晶氧化锆（3Y-TZP）陶瓷,分析着色后材料的显微和晶相结构,并测定其理化、机械及抗低温时效性能。方法将TZ-3Y-S粉体与一定组分的着色剂球磨混合后,在200 MPa压力下等静压成型,先于1 050 ℃预烧结2 h,然后在1 500 ℃终烧结2 h,烧制5种具有一定颜色的氧化锆材料,测量烧结体的密度、收缩率、热膨胀系数、维氏硬度、三点弯曲强度、断裂韧性和化学稳定性;通过扫描电镜和X线衍射观察着色后材料的显微和晶相结构,并测试着色对材料抗低温时效性能的影响。结果着色后3Y-TZP陶瓷烧结密度在99.7%以上,烧结收缩率约20%,热膨胀系数为11×10-6·℃-1;晶粒大小均匀,主要断裂方式为穿晶断裂,主晶相为四方相氧化锆（t-ZrO2）;在弱酸性条件下具有较好的化学稳定性;5组着色氧化锆陶瓷的三点弯曲强度较未着色组略有降低,但均在900 MPa以上,断裂韧性略有提高,经低温时效处理后四方相到单斜相（m-ZrO2）的相变量约40%,但弯曲强度没有降低。结论3Y-TZP陶瓷经过着色后,具有优良的理化和机械性能,能够满足牙科临床应用的要求。     

添加相氧化铝对牙科纳米氧化锆陶瓷性能的影响

目的 通过测定不同Al2O3含量的牙科纳米氧化锫复合陶瓷材料的烧结密度、力学性能和可见光积分透射比,探讨Al2O3添加量对复合陶瓷力学性能及半透明性的影响.方法 分别测量Al2O3质量百分数分别为2.5%、5.0%、7.5%、10.0%的Al2O3组和对照组(不含Al2O3)氧化锆陶瓷试件的烧结密度、三点弯曲强度和断裂韧性,采用分光光度计测量可见光积分透射比,扫描电镜观察试件断面形貌.结果 对照组试件常压烧结下烧结密度为(6.04±0.03)g/cm3,接近理论密度,三点弯曲强度为(1100.27±54.82)MPa,断裂韧性为(4.96±0.35)MPa·m1/2,透射比高达17.03%;2.5%、5.0%、7.5%、10.0%Al2O3组随Al2O3含量的增加,试件的烧结密度和透射比下降,断裂韧性有所提高;Al2O3 4组间三点弯曲强度的差异无统计学意义(P>0.05);10.0%Al2O3组试件的断裂韧性为(6.13±0.44)MPa·m1/2,透射比明显降低至6.21%.Al2O3对四方氧化锆晶粒的大小和分布无明显影响.结论 添加Al2O3可影响氧化锆复合陶瓷的力学性能和半透明性,添加复合相需兼顾临床对陶瓷材料力学性能和透光性的要求.     

反复烧结对氧化锆支架与饰瓷结合强度的影响

目的 研究多次烧结对牙科氧化锆陶瓷与饰面瓷双层瓷结构力学性能的影响,为临床及技工的操作提供理论依据.方法 采用粉浆涂塑法将Kiss饰面瓷堆塑在直径10 mm、厚1 mm的氧化锆试件上,将20个试件随机分为A、B、C、D四组,按照常规烧结程序分别烧结不同次数,其中A组3次、B组5次、C组7次、D组9次.在万能材料试验机上测试试件界面的剪切强度.采用SPSS 11.0统计软件对测试结果进行统计分析.使用扫描电镜(SEM)等研究试件界面的形貌.结果 随着烧结次数的增加,A、B、C、D四组试件的剪切强度依次为(28.07 ± 2.40)Mpa、(31.91 ± 1.47)Mpa、(27.27 ± 3.10)Mpa、(21.68 ± 1.51)Mpa.其中,D组的剪切强度明显低于其他三组,差异具有统计学意义(P<0.05);而B组试件的剪切强度均数较A组、C组略高,差异也具有统计学意义(P<0.05);A组与C组的剪切强度均数差异无统计学差异(P>0.05).SEM观察发现多次烧结后界面间的气孔和裂纹增多,结合性能降低.结论 超过一定的烧结次数时,烧结次数的增加对氧化锆陶瓷与饰面瓷双层瓷的结合强度有影响.技工室操作时应尽量减少对氧化锆陶瓷与饰面瓷双层瓷的烧结次数.     

改良液式冲蚀对3Y-TZP氧化锆基底与饰面瓷结合强度的影响

目的:探讨采用改良液式冲蚀方式对3Y-TZP氧化锆基底表面进行冲蚀后,对其与饰面瓷间结合强度的影响.方法:制作[8 mm×8 mm×3 mm(±0.02)]氧化锆试件块174个,根据不同尺寸的刚玉磨粒、不同的喷砂压强、不同的喷砂时间,采用传统喷砂方式进行分组处理(实验组),在氧化锆处理面上饰面瓷.表面未做处理的氧化锆试件直接上饰面瓷作为对照组,应用电子万能测力计检测各组试件与饰面瓷间的最大剪切力,计算剪切强度.分别用传统干式喷砂、改良液式冲蚀方式在相同条件下(150 μm,0.6 MPa,30 s)处理氧化锆试件块,用扫描电镜下观察处理面,再上饰面瓷,计算剪切强度,与对照组进行组间比较.采用SPSS17.0软件包对数据进行统计学分析.结果:采用传统干式喷砂方式,在0.4 MPa压强作用下,以110 μm A12O3喷砂粉喷砂20 s时,氧化锆与饰面瓷之间的剪切强度最大,显著大于对照组(P＜0.05);改良液式冲蚀组饰面瓷的结合强度显著大于传统干式喷砂处理组及对照组(P＜0.01).扫描电镜下可见,采用改良液式冲蚀的试件表面呈现均匀的粗糙面:采用传统干式喷砂处理的试件表面呈现不均匀的粗糙面,部分位置可见微裂纹.结论:对3Y-TZP氧化锆表面喷砂,能够增强其与饰面瓷间的结合强度;改良液式冲蚀比传统干式喷砂更适用于3Y-TZP氧化锆的表面处理.     

TZ-3Y-E粉体的烧结及力学性能实验分析

目的:对纳米氧化锆TZ-3Y-E粉体的烧结及力学性能进行实验分析。方法:TZ-3Y-E粉体200 MPa等静压成型,于不同温度下烧结,测试烧结体密度并检测其线性收缩,弯曲强度和断裂韧性。结果:随着温度的升高,纳米氧化锆的烧结密度和线性收缩呈上升的趋势,在1 300℃时体积密度达到6.09 g/cm3,最大线性收缩率为21.41%。1 400℃时的机械性能最好,三点弯曲强度和断裂韧性分别为(1 536.37±85.49)MPa,(5.07±1.34)MPa.m1/2。结论:TZ-3Y-E粉体能在低温下烧结,力学性能优良,能够满足口腔全瓷修复材料的要求。     

不同处理剂对氧化锆与正畸托槽间黏结强度的影响

目的:比较不同表面处理剂对氧化锆修复体表面与正畸托槽间黏结强度的影响.方法:将50个氧化锆陶瓷试件随机分为5组(n=10),进行喷砂和磷酸处理,A组为对照组;B组以硅烷偶联剂处理;C组以硅烷偶联剂+SE Bond 处理;D组以Z-PrimeTM Plus氧化锆处理剂处理;E组以Z-PrimeTM Plus+SE Bond处理.所有试件均用3M Transbond 光固化树脂黏结剂与右上中切牙的托槽黏结,经24 h、37℃恒水浴后,进行抗剪切强度测试;去除托槽后,对氧化锆表面黏结剂残留指数进行统计.其中,每组1个氧化锆表面处理后用扫描电镜观察其表面形态变化,并对氧化锆及处理剂进行红外光谱分析.采用SPSS17.0软件包对数据进行统计学分析.结果:各组的抗剪切强度分别为A组(3.12±0.84) MPa、B组(1.92±0.83) MPa、C组(5.26±0.80) MPa、D组(6.54±0.98)MPa和E组(9.47±2.11) MPa,各组间差异均具有显著性(P＜0.05).A组和B组残留指数最低,E组最高.D组和E组达到了有效的黏结强度.结论:单独使用氧化锆处理剂能获得有效的黏结强度,但是略偏低.建议Z-PrimeTM Plus+SE Bond处理联合使用,以达到正畸临床所需的较高的黏结强度.     

The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

STATEMENT OF PROBLEM

Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.

PURPOSE

The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM).

MATERIAL AND METHODS

Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05).

RESULTS

The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa.

CONCLUSION

The monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.     

Chemical solubility and flexural strength of zirconia-based ceramics

PURPOSE: This study was undertaken to investigate the chemical solubility and flexural strengths of 3 zirconia-based dental ceramics: In-Ceram Zirconia (IZ), In-Ceram 2000 YZ CUBES (YZ Zirconia) (Vita Zahnfabrik), and Cercon (Dentsply). A pressable lithium disilicate-reinforced glass ceramic (IPS Empress 2, Ivoclar Vivadent) was used as a control. MATERIALS AND METHODS: Ten block specimens (12 x 6 x 4 mm) of each ceramic material were prepared for chemical solubility testing. Each specimen was refluxed in 4% acetic acid solution for 16 hours. The percentage loss of mass and the loss of mass per unit of surface area for each specimen were calculated. Ten bar-shaped (21 x 5 x 2 mm) and 10 disk-shaped (16 mm diameter, 1.2 mm thickness) specimens of each ceramic material were prepared and tested for uniaxial flexural strength (UFS) and biaxial flexural strength (BFS). X-ray diffraction analyses were conducted to determine the relative amount of the monoclinic phase of the as-sintered and fractured surfaces of the zirconia ceramics. RESULTS: There were no significant differences among the ceramics in chemical solubility by percentage mass or mass/surface area. For UFS, YZ Zirconia (899 +/- 109 MPa) > Cercon (458 +/- 95 MPa) IZ (409 +/- 60 MPa) > Empress 2 (252 +/- 36 MPa). For BFS, YZ Zirconia (1,107 +/- 116 MPa) > Cercon (927 +/- 146 MPa) > IZ (523 +/- 51 MPa) > Empress 2 (359 +/- 43 MPa). The fractured YZ Zirconia surface contained approximately 5 times as much monoclinic phase compared to that of its intact surface. The fractured IZ and Cercon surfaces contained approximately twice as much monoclinic phase compared to those of intact surfaces. CONCLUSION: The ceramics tested all satisfied the chemical solubility allowance required of core ceramic material (type I, Class 1 or type II, Class 1) according to the International Organization for Standardization 6872:1995(E) specifications on dental ceramic. The zirconia-based ceramics possessed significantly higher flexural strengths than the control lithium disilicate ceramic. Their clinical application appears sufficiently promising for long-term clinical studies to be undertaken.     

牙科着色氧化钇稳定四方多晶氧化锆陶瓷的制备及颜色性能

目的添加不同着色剂组合配制着色的牙科氧化钇稳定四方多晶氧化锆（3Y-TZP）陶瓷，并测定其颜色性能。方法将TZ-3Y-S粉体与一定组分的着色剂球磨混合后，在200 MPa压力下等静压成型，在1 500 ℃烧结2 h，烧制5种具有一定颜色的氧化锆材料，每个颜色组分别制备10 mm×10 mm×0.5 mm和10 mm×10 mm×1 mm着色氧化锆陶瓷片，在黑色背景下用柯尼卡美能达CM-2600d分光光度计进行颜色测定，并与VITA In-Ceram YZ染色液比色板颜色作比较。结果通过对粉体进行着色，配制出具有一定颜色的本体着色氧化锆陶瓷材料，颜色明度逐级降低，饱和度逐渐增大，2种厚度3Y-TZP陶瓷的颜色片色差较小，颜色空间范围是L*：67.76～77.78；a*：-2.19～3.80；b*：12.13～25.01。与VITA In-Ceram YZ染色液比色板相比，颜色空间近似，但明度的最低值仍较高。结论着色氧化锆陶瓷材料适宜用于临床上与饰面瓷颜色匹配，有必要再进一步研究低明度的着色氧化锆色片。     

Four-point flexural strength and microtensile bond strength of digitally and conventionally veneered zirconia

This study intended to evaluate the effect of digital veneering on four-point flexural strength (FS) and microtensile bond strength (μTBS) of veneered zirconia. Two different zirconia blocks, a lithium disilicate and a feldspathic ceramic block, and two different layering ceramics were used. IPS e.max Zir CAD (ZC) and Vita In-Ceram YZ (YZ) with yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) were used as substructures. IPS e.max CAD (LD), Vita Mark II (VMII), IPS e.max Ceram (EC) and Vita VM9 (VM9) were used for veneering. Resin cement and fusion ceramic were placed between veneer and zirconia substructure for digital veneering. A total of one hundred and fifty specimens in five groups (n = 30) were prepared for FS and tested in universal machine at 1.0 mm/min. One hundred specimens in five groups (n = 20) were obtained for the μTBS and tested at 1.0 mm/min. Statistical analysis was made by one way ANOVA and Tukey HSD. Conventional veneering showed statistically significant FS. ZC veneered with EC had the highest mean FS and the lowest was obtained in groups veneered through resin cement. YZ layered with VM9 had the highest mean μTBS. ZC veneered through fusion ceramic and YZ veneered through resin cement showed significantly lower and similar μTBS.     

Mechanical behavior and microstructural characterization of different zirconia polycrystals in different thicknesses

PURPOSETo characterize the microstructure of three yttria partially stabilized zirconia ceramics and to compare their hardness, indentation fracture resistance (IFR), biaxial flexural strength (BFS), and fatigue flexural strength.MATERIALS AND METHODSDisc-shaped specimens were obtained from 3Y-TZP (Vita YZ HT), 4Y-PSZ (Vita YZ ST) and 5Y-PSZ (Vita YZ XT), following the ISO 6872/2015 guidelines for BFS testing (final dimensions of 12 mm in diameter, 0.7 and 1.2 ± 0.1 mm in thicknesses). Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed, and mechanical properties were assessed by Vickers hardness, IFR, quasi-static BFS and fatigue tests.RESULTSAll ceramics showed similar chemical compositions, but mainly differed in the amount of yttria, which was higher as the amount of cubic phase in the diffractogram (5Y-PSZ > 4Y-PSZ > 3Y-TZP). The 4Y- and 5Y-PSZ specimens showed surface defects under SEM, while 3Y-TZP exhibited greater grain uniformity on the surface. 5Y-PSZ and 3Y-TZP presented the highest hardness values, while 3Y-TZP was higher than 4Y- and 5Y-PSZ with regard to the IFR. The 5Y-PSZ specimen (0.7 and 1.2 mm) showed the worst mechanical performance (fatigue BFS and cycles until failure), while 3Y-TZP and 4Y-PSZ presented statistically similar values, higher than 5Y-PSZ for both thicknesses (0.7 and 1.2 mm). Moreover, 3Y-TZP showed the highest (1.2 mm group) and the lowest (0.7 mm group) degradation percentage, and 5Y-PSZ had higher strength degradation than 4Y-PSZ group.CONCLUSIONDespite the microstructural differences, 4Y-PSZ and 3Y-TZP had similar fatigue behavior regardless of thickness. 5Y-PSZ had the lowest mechanical performance.     

Fracture resistance of zirconia FPDs with adhesive bonding versus conventional cementation

This study investigated the fracture resistance of three different zirconia fixed partial dentures (FPDs) with different cementation methods. Forty-eight three-unit FPDs were adhesively bonded (AB) or conventionally cemented (CC). Sixteen glass-infiltrated zirconia FPDs were used as a control. Fracture resistance was determined after aging. The zirconia systems showed no significant different fracture forces with the different bonding methods (CC: Cercon [1,231.5 ± 410.1 N], Ceramill [1,311.3 ± 318.3 N], Vita YZ [1,269.0 ± 317.4 N]; AB: Cercon [1,072.3 ± 516.7 N], Ceramill [1,358.6 ± 176.4 N], Vita YZ [1,270.6 ± 267.6N]) or between the different materials. The control group provided significantly lower fracture strength. Regarding fracture resistance, adhesive bonding or conventional cementation of zirconia FPDs showed no restrictions for posterior application.     

Fracture resistance of all-ceramic zirconia bridges with differing phase stabilizers and quality of sintering.

OBJECTIVES: The mechanical properties of zirconia ceramics are affected of stabilizing oxides and quality of sintering. The purpose of this study was to investigate the fracture resistance of frameworks manufactured using prefabricated zirconia blanks with differing stabilizing oxides and quality of sintering. METHODS: After dynamic loading in water, the fracture resistance was determined of stylized three-unit fixed partial dentures made of prefabricated homogenous ceramic green-body yttria-stabilized zirconia (Y-TZP) blanks (Vita YZ) or of densely-sintered magnesia partially stabilized zirconia (Mg-PSZ) blanks (Denzir-M); (i) as supplied from the manufacturer, (ii) after subjection to heat treatment in a way similar to veneering, and (Hi) after veneering with a feldspar-based ceramic. RESULTS: After veneering, the load at fracture of the Vita YZ specimens was significantly higher (p<0.05) than that of Denzir-M. The load necessary to fracture Denzir-M as supplied after machining was significantly (p<0.05) higher than that of heat-treated Denzir-M, Vita YZ as supplied and heat-treated Vita YZ specimens. There was no significant difference (p>0.05) between the heat-treated and veneered Denzir-M specimens. For Vita YZ the load at fracture of the veneered specimens was significantly (p<0.05) higher than of those as supplied or heat-treated, whereas no significant difference (p>0.05) was seen between heat-treated Vita YZ and Vita YZ specimens as supplied. SIGNIFICANCE: The fracture strength of the Vita YZ specimens increased considerably after veneering. Denzir-M and Vita YZ seem to be interesting alternatives for use as core materials in all-ceramic restorations. Long-term studies are, however, necessary before general clinical recommendations can be issued.     

In vitro evaluation of low-temperature aging effects and finishing procedures on the flexural strength and structural stability of Y-TZP dental ceramics

STATEMENT OF PROBLEM: Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic material has been reported to possess exceptionally high flexural strength; however, the strength of Y-TZP ceramics can be affected by surface treatments performed by dental laboratory technicians and by intraoral conditions. PURPOSE: This study investigated the influence of low-temperature-degradation (LTD) treatment, airborne-particle abrasion, and polishing on the flexural strength and structural stability of a Y-TZP ceramic material. MATERIAL AND METHODS: By sectioning zirconia ceramic blocks (Vita In-Ceram YZ blocks) into 25 x 4 x 2-mm bars, 310 specimens were fabricated and divided into 9 groups: Group C, as-sintered (control); group B24h, boiled in water for 24 hours; group B7d, boiled in water for 7 days; group H6h, stored in humidified air at 250 degrees C for 6 hours; group H24h, stored in humidified air at 250 degrees C for 24 hours; group H7d, stored in humidified air at 250 degrees C for 7 days; group P, polished; group A, airborne-particle abraded; and group AB, airborne-particle abraded and boiled for 7 days. The flexural strengths (MPa) of all specimens were determined by using a 3-point bending test. The variability was analyzed by using Weibull statistics. Pairwise differences among the 9 groups were evaluated by using confidence intervals (95%) for scale and shape parameters. From every block used, 8 specimens were obtained and every specimen was marked according to the location of its origin from the original block. Surfaces of the specimens were evaluated by using scanning electron microscopy (SEM) at various magnifications. X-ray diffraction analysis was performed to identify possible tetragonal-to-monoclinic phase transformations. Energy dispersive spectroscopy (EDS) was used to obtain information on the chemical composition. RESULTS: Aging or "finishing" treatments had no significant negative effects on flexural strengths. Mean flexural strengths ranged from 796.7 to 950.2 MPa. Group A exhibited the highest mean flexural strength (950.2 MPa). Weibull modulus values ranged between 5.6 and 9.3. Tetragonal-to-monoclinic phase transformation was detected for a specimen boiled for 24 hours. More tetragonal-to-monoclinic phase transformation was detected for specimens boiled for 7 days and stored in humidified air at 250 degrees C for 7 days. The SEM examination of fractured surfaces revealed sintering defects, and EDS analysis showed less yttria concentration on Y-TZP specimens that were boiled for 7 days. CONCLUSION: Within the limitations of this study, the results suggested that the LTD procedures and the polishing treatment used did not reduce the flexural strengths of zirconia bars. Airborne-particle abrasion increased the flexural strength of specimens. CLINICAL IMPLICATIONS: Although polishing, airborne-particle abrasion, and various low-temperature degradation (LTD) treatments did not significantly degrade the strength of the Y-TZP ceramic material, LTD resulted in loss of yttria. Over time, gradual dissolution of yttria could decrease the tetragonal-phase stability and long-term clinical serviceability of this dental ceramic material.     

钇稳定氧化锆基底材料与饰面瓷结合性能的实验研究

目的考察国产氧化钇稳定四方晶体氧化锆（3Y-TZP）与4种氧化锆专用饰面瓷界面的结合性能。方法粉浆涂塑方法分别将VITA VM9、SHOFU VINTAGE ZR、IPS e.max Ceram、Cercon ceram kiss 4种氧化锆专用饰面瓷烧结在15 mm×5 mm×5 mm的3Y-TZP核瓷试件上,另外制作相同尺寸镍铬合金烤瓷试件作为对照,测试界面剪切强度。制作氧化锆基底与饰面瓷双层瓷试件,扫描电镜（SEM）观察结合界面微观形貌;能谱分析（EDS）检测界面元素分布。结果氧化锆与VITA VM9、SHOFU VINTAGE ZR、IPS e.max Ceram、Cercon ceram kiss 4种氧化锆专用饰面瓷的剪切强度分别为（18.83±1.77）MPa、（23.83±7.05）MPa、（17.87±2.30）MPa、（22.26±7.45）MPa,各组与金属烤瓷对照组比较,差异均无统计学意义（P＞0.05）。各3Y-TZP烤瓷组试件破坏模式以界面破坏为主。扫描电镜观察氧化锆和饰面瓷结合界面结合紧密;能谱分析结果显示二者存在化学元素渗透。结论国产3Y-TZP与饰面瓷材料界面结合良好,可以满足临床需要。