牙科玻璃渗透氧化铝陶瓷弯曲强度Weibull分析和循环载荷下亚临界裂纹扩展研究

目的：研究牙科玻璃渗透氧化铝陶瓷（IA,In-Ceram Alumina）弯曲强度（σ）Weibull分析意义和循环载荷下亚临界裂纹扩展（SCG）情况。方法：分别采用三点弯曲强度测量方法（3p）和循环疲劳（F）测试方法测得15个条形IA样本的弯曲强度以及15个条形IA样本的循环疲劳断裂循环次数,数据采用Weibull方法分析;亚临界裂纹扩展（SCG）行为通过裂纹扩展速度和最大应力强度因子（KImax）的函数关系来描述。结果：IA的Weibull模数为7.9,特征强度（σ63.21）为438.3MPa。IA在循环载荷下发生亚临界裂纹扩展后导致材料断裂,在应力强度因子K1为临界应力因子KIC的55%时发生裂纹传播。结论：牙科玻璃渗透氧化铝陶瓷循环载荷下存在亚临界裂纹扩展;采用弯曲强度测试法并结合使用Weibull分析方法能加深对口腔陶瓷修复失败机制的理解。     

不同环境对玻璃渗透氧化铝陶瓷亚临界裂纹扩展的影响’

、目的：研究口腔临床修复中常用的玻璃渗透氧化铝陶瓷（IA,In-CeramAlumina,IA）在干燥环境和潮湿环境下的亚临界裂纹扩展（SCG）行为的区别。方法：通过三点弯曲强度测量方法测得15个IA样本的强度数据,采用循环疲劳测试法测出干燥环境下15个IA样本以及在潮湿环境下15个IA样本的循环疲劳断裂次数数据;SCG行为通过裂纹扩展速率和应力强度因子（K1）的函数关系来描述。结果：不同环境下IA在循环载荷下发生亚临界裂纹扩展后导致材料断裂,在干燥环境下应力强度因子K1为临界应力因子Knc面的46％时发生裂纹传播;在潮湿环境下应力强度因子K1为临界应力因子Knc的40％时发生裂纹传播。结论：IA在循环载荷下存在SCG行为,当应力强度因子相同时,潮湿环境下样品的裂纹扩展速率较大,说明潮湿环境能加速亚临界裂纹扩展,符合口腔的实际情况。     

IPS－Empress2玻璃陶瓷复层结构亚临界裂纹扩展研究

目的：研究牙科美学陶瓷（IPS－Empress 2）的层状复合结构亚临界裂纹（以下简称SCG）扩展情况。方法：采用Weibull法分析由三点弯曲强度测量方法（3p）获得15个IPS－Empress 2的复层结构样本的弯曲强度数据和由循环疲劳测试（F）获得的15个IPS－Empress 2的复层结构样本循环疲劳断裂次数数据;通过帕里斯定律分析试件在Hertzian循环加载后的亚临界裂纹扩展情况,SCG行为通过裂纹扩展速度和应力强度因子（K1）的函数关系来描述。结果：通过Weibull法得到IPS－Empress 2的复层结构的Weibull模数为7．7。 IPS－Empress 2复层结构在循环载荷下发生亚临界裂纹扩展后导致材料断裂,在应力强度因子K1为临界应力因子KIC的52％时发生裂纹传播。结论：牙科陶瓷层状复合结构循环载荷下存在亚临界裂纹扩展。     

两种牙科陶瓷材料层状结构循环疲劳行为的对比研究

目的比较EmpressⅡ热压铸造陶瓷和GI- Ⅱ型氧化铝渗透陶瓷材料层状复合结构经Hertzian循环加载疲劳后强度的变化以及损伤模式的差异。方法应用Hertzian接触实验方法对EmpressⅡ热压铸造陶瓷和GI- Ⅱ型氧化铝渗透陶瓷标准试件进行循环加载,然后测试加载后试件的临界载荷。结果EmpressⅡ热压铸造陶瓷复合结构试件经105次循环后的临界载荷与未经循环加载组的临界载荷差别有统计学意义（P<0.05）;GI- Ⅱ型氧化铝渗透陶瓷复合结构试件在循环加载疲劳实验中,各组临界载荷变化均无统计学差别。结论GI- Ⅱ型氧化铝渗透陶瓷在循环疲劳实验中表现出较好的耐疲劳特性,可能与其材料本身的显微结构有关。EmpressⅡ热压铸造陶瓷以脆性损伤模式为主。     

IPS-Empress2玻璃陶瓷弯曲强度的测试及意义

目的：研究IPS-Empress2玻璃陶瓷弯曲强度的统计意义。方法：采用三点弯曲强度测量方法测量40个IPS-Empress2玻璃陶瓷的弯曲强度并与Weibull分析方法相结合,求该陶瓷的Weibull模数（m）及其强度与生存概率的对应关系。结果：IPS-Empress2玻璃陶瓷Weibull模数为7．7。其1％、5％、63．21％破坏概率的弯曲强度分别为301．5MPa、319．2MPa、421．1MPa。结论：IPS-Empress2玻璃陶瓷具有低的Weibull模数以及欠佳的材料结构可靠性,所以其在高应力受力区破坏的概率大。采用弯曲强度测试法并结合使用Weibull分析方法能加深对口腔陶瓷修复失败机制的理解。     

牙科全瓷材料的裂纹扩展模式和影响因素

全瓷修复体具有良好的美观性和生物安全性,在临床上已经得到广泛应用。但是其本身是一种脆性材料,在反复咀嚼作用力下常常出现裂纹扩展、材料失效。本文回顾了全瓷材料裂纹研究的相关实验方法,并针对单层、双层、三层结构模型的损伤模式(包括脆性模式、准塑性模式和放射状裂纹)及影响因素进行综述。     

提高牙科陶瓷强度的研究

陶瓷是制作义齿的重要材料。瓷修复体色泽美观,生物相容性好。但是,瓷性脆,易折裂。本文从表面处理、内部增强和应用高强度底层增强等方面阐述了提高牙科陶瓷强度的研究进展,旨在为我国牙科陶瓷的应用研究提供帮助。     

厚度配比对2种牙科陶瓷疲劳行为的影响研究

目的考察不同厚度配比的EmpressⅡ热压铸造陶瓷和GI-Ⅱ型氧化铝渗透陶瓷层状复合结构经Hertzian循疲劳前后强度的变化。方法分别制作不同厚度配比EmpressⅡ热压铸造陶瓷和GI-Ⅱ型氧化铝渗透陶瓷圆盘状试件,应用Hertzian接触实验方法对这些试件进行循环加载,然后测试105循环加载前后试件的临界载荷。结果EmpressⅡ热压铸造陶瓷和GI-Ⅱ型氧化铝渗透陶瓷在经Hertzian循环加载后,临界载荷力的平均值比加载前均明显下降（P<0.05）,并且载荷力随底层瓷厚度的下降而降低。GI-Ⅱ氧化铝渗透陶瓷在加载前后的临界载荷均明显高于EmpressⅡ热压铸造陶瓷（P<0.05）。结论循环疲劳能显著降低EmpressⅡ热压铸造陶瓷和GI-Ⅱ型氧化铝渗透陶瓷材料的强度,后者在抗碎裂能力和耐受疲劳方面均优于前者,底层瓷的强度和厚度是决定这2种材料临界载荷力的大小的主要因素。     

CAD/CAM加工的渗透陶瓷的弯曲强度和Weibull分析

目的:利用弯曲强度和Weibull分析方法对可被CAD/CAM技术加工的渗透陶瓷的结构可靠性进行分析,为临床选择应用该陶瓷材料提供依据。方法:采用硫酸铝铵两步煅烧法制备的超细氧化铝粉体,经工业预烧结形成可渗透的机加工陶瓷块,经过镧铝硅酸盐玻璃渗透形成渗透陶瓷复合体。测试30个样本的三点弯曲强度,并计算Weibull模数(m)及破坏概率为1%和5%时的弯曲强度。采用X线衍射分析(XRD)并结合扫描电子显微镜(SEM),分别对材料的物相组成和微观形貌进行分析。结果:渗透陶瓷复合体的强度为(375.5±66.88)MPa,Weibull模数(m)为6.2,1%破坏概率时的弯曲强度为191.79MPa,5%破坏概率时的弯曲强度为249.83MPa。扫描电镜可见氧化铝预烧结体为连续多孔立体网状结构,开孔结构分布均匀;渗透复合体为致密的陶瓷复合体。XRD表明主晶相为α-alumina。结论:与单纯测试材料的弯曲强度相比,采用弯曲强度测试法并结合Weibull分析方法,能加深对口腔陶瓷修复失败机制的理解,更加有效地利用材料的平均强度值指导口腔陶瓷修复设计。     

Relative flexural strength of dental restorative ceramics

The relative flexural strengths of ten brands of dental restorative ceramics were evaluated by a three-point bending test. The materials consisted of three low-fusing and one high-fusing feldspathic porcelains and six reinforced dental restorative ceramics which are currently in clinical use. The reinforced ceramic materials investigated utilized a number of different strengthening processes, including alumina and ceramic fiber reinforcement and controlled crystallization. The results of the investigation indicate that significant differences exist among the measured breaking strengths of the various materials. The processes of controlled crystallization and alumina reinforcement appear to be adequate means of improving the bending strength of restorative dental ceramics.     

Analysis of subcritical crack growth in dental ceramics using fracture mechanics and fractography.

OBJECTIVES: The aim of this study was to test the hypothesis that the flexural strengths and critical flaw sizes of dental ceramic specimens will be affected by the testing environment and stressing rate even though their fracture toughness values will remain the same. METHODS: Ceramic specimens were prepared from an aluminous porcelain (Vitadur Alpha; VITA Zahnfabrik, Bad S?ckingen, Germany) and an alumina-zirconia-glass composite (In-Ceram Zirconia; VITA Zahnfabrik). Three hundred uniaxial flexure specimens (150 of each material) were fabricated to dimensions of 25 mmx4 mmx1.2 mm according to the ISO 6872 standard. Each group of 30 specimens was fractured in water using one of four different target stressing rates ranging on a logarithmic scale from 0.1 to 100 MPa/s for Vitadur Alpha and from 0.01 to 10 MPa/s for In-Ceram Zirconia. The fifth group was tested in inert environment (oil) with a target stressing rate of 100 MPa/s for Vitadur Alpha and 1000 MPa/s for In-Ceram Zirconia. The effects of stressing rate and environment on flexural strength, critical flaw size, and fracture toughness were analyzed statistically by Kruskal-Wallis one-way ANOVA on ranks followed by post hoc comparisons using Dunn's test (alpha=0.05). In addition, 20 Vitadur Alpha specimens were fabricated with controlled flaws to simplify fractography. Half of these specimens were fracture tested in water and half in oil at a target stressing rate of 100 MPa/s, and the results were compared using Mann-Whitney rank sum tests (alpha=0.05). A logarithmic regression model was used to determine the fatigue parameters for each material. RESULTS: For each ceramic composition, specimens tested in oil had significantly higher strength (P0.05). Specimens tested at faster stressing rates had significantly higher strength (P0.05). Regarding critical flaw size, stressing rate had a significant effect for In-Ceram Zirconia specimens (P0.05). Fatigue parameters, n and lnB, were 38.4 and -12.7 for Vitadur Alpha and were 13.1 and 10.4 for In-Ceram Zirconia. SIGNIFICANCE: Moisture assisted subcritical crack growth had a more deleterious effect on In-Ceram Zirconia core ceramic than on Vitadur Alpha porcelain. Fracture surface analysis identified fracture surface features that can potentially mislead investigators into misidentifying the critical flaw.     

Slow crack growth and reliability of dental ceramics

Objective

To determine the slow crack growth (SCG) and Weibull parameters of five dental ceramics: a vitreous porcelain (V), a leucite-based porcelain (D), a leucite-based glass-ceramic (E1), a lithium disilicate glass-ceramic (E2) and a glass-infiltrated alumina composite (IC).

Methods

Eighty disks (Ø 12 mm × 1.1 mm thick) of each material were constructed according to manufacturers’ recommendations and polished. The stress corrosion susceptibility coefficient (n) was obtained by dynamic fatigue test, and specimens were tested in biaxial flexure at five stress rates immersed in artificial saliva at 37 °C. Weibull parameters were calculated for the 30 specimens tested at 1 MPa/s in artificial saliva at 37 °C. The 80 specimens were distributed as follows: 10 for each stress rate (10⁻², 10⁻¹, 10¹, 10² MPa/s), 10 for inert strength (10² MPa/s, silicon oil) and 30 for 10⁰ MPa/s. Fractographic analysis was also performed to investigate the fracture origin.

Results

E2 showed the lowest slow crack growth susceptibility coefficient (17.2), followed by D (20.4) and V (26.3). E1 and IC presented the highest n values (30.1 and 31.1, respectively). Porcelain V presented the lowest Weibull modulus (5.2). All other materials showed similar Weibull modulus values, ranging from 9.4 to 11.7. Fractographic analysis indicated that for porcelain D, glass-ceramics E1 and E2, and composite IC crack deflection was the main toughening mechanism.

Significance

This study provides a detailed microstructural and slow crack growth characterization of widely used dental ceramics. This is important from a clinical standpoint to assist the clinician in choosing the best ceramic material for each situation as well as predicting its clinical longevity. It also can be helpful in developing new materials for dental prostheses.     

Effect of amount of grinding on flexural strength of dental ceramics

The aim of this study was to determine a suitable amount of grinding of a flexural test specimen for clinical evaluation of dental ceramics. Three dental ceramics (Crys-Cera, OCC and IPS Empress Cosmo) were selected. Five types of bar-shaped patterns were prepared for a three-point bending test, and four types of disk-shaped patterns for a biaxial flexural test. Ceramic specimens were fabricated using these patterns in accordance with the manufacturers' instructions. All specimens were ground with diamond polishing pads to yield either bar or disk specimens with the same final geometry. The surface roughness and X-ray diffraction (XRD) patterns of the specimens were examined. The flexural strength values of Crys-Cera and Empress decreased with increasing amounts of grinding, while that of OCC increased with increased grinding. The surfaces of all specimens were smoother when the amount of grinding was deeper. The XRD patterns of Crys-Cera and Empress changed with increased grinding; however, that of OCC did not change regardless of the extent of grinding. The flexural strengths of three dental ceramics differed with the amount of grinding probably because of changes of surface roughness and crystalline component composition. Unground specimens provided important insight into clinical failure modes.     

Effect of test method on flexural strength of recent dental ceramics

The purpose of the present study was to evaluate the relationships among three flexural strengths of recent dental ceramics using 3-point and 4-point bending tests and biaxial flexural test. Three brands of porcelain for veneering (d.SIGN, Supper porcelain AAA, Vintage Hallo), two injectable ceramics (Empress 2, OPC 3G), and one castable ceramic (Crys-Cera) were used. Twenty bar-shaped and 10 disc-shaped specimens of each ceramic type were prepared according to manufacturers' instructions, polished, and subjected to 3-point and 4-point bending tests and biaxial flexural test, respectively. Three flexural strengths for each ceramics were compared using one-way analysis of variance and Tukey comparison, and also investigated by Weibull analysis. The biaxial flexural strength and 3-point bending strength of all ceramics, except OPC 3G and Crys-Cera, were significantly greater than the corresponding 4-point bending strength. As for OPC 3G and Crys-Cera, their biaxial flexural strengths were significantly greater than their 3-point bending strengths, which is contrary to the other ceramics. The Weibull moduli ranged from 6.6 to 20.8. The Weibull moduli of examined ceramics, except Crys-cera, were statistically insignificant regardless of test methods.     

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.     

Biaxial flexural strength and translucent characteristics of dental lithium disilicate glass ceramics with different translucencies

PurposeThe aim of this study was to evaluate the biaxial flexural strength and translucent characteristics of dental lithium disilicate glass ceramics with different translucencies.MethodsTwo heat pressed lithium disilicate glass ceramics (IPS e.max Press and an experimental ceramic) and one computer aided design/ computer aided manufacture (CAD/CAM) lithium disilicate glass ceramic (IPS e.max CAD) with different translucencies were evaluated. Disk-shaped specimens of each group were subjected to a biaxial flexural strength (BFS) test. Translucent parameters (TP) were also tested at 0.5 mm and 1.0 mm thickness, respectively. X-ray diffraction (XRD) and SEM were used for crystalline and microstructural analysis.ResultsBFS values of two heat pressed lithium disilicate glass ceramics were significantly higher than the CAD/CAM counterpart. No difference in BFS between two heat pressed glass ceramic was found. There were significant differences in BFS and TP values among the tested subgroups with different translucencies for IPS e.max Press and IPS e.max CAD. No difference in crystalline composition was found among the tested glass ceramics, but microstructure with shorter and wider crystal was revealed for IPS e.max CAD ceramics.ConclusionsLithium disilicate glass ceramics with different translucencies demonstrated different BFS and TP values.