氧化锆对二硅酸锂玻璃陶瓷力学性能的影响

目的:测定牙科氧化锆-二硅酸锂玻璃陶瓷复合材料(ZTCLDC)的力学性能,探讨氧化锆质量分数变化对ZTCLDC力学性能的影响及机制。方法:向制备好的二硅酸锂基础玻璃粉体中分别添加不同质量分数的ZrO(21%,2%,3%,4%),静压成型晶化热处理,每组中的半数试件进行牙科热压铸处理,分别测试热压铸前后的三点弯曲强度及断裂韧性;扫描电镜观察晶体微观结构;X射线衍射分析其晶相组成。结果:热压铸前,ZTCLDC抗弯强度和断裂韧性随ZrO2含量的增加而升高;热压铸后,ZTCLDC抗弯强度随ZrO2含量的增加而降低,ZrO2加入量为4%时,压铸后的断裂韧性最高为4.3 MPa.m1/2。结论:ZrO2对实验二硅酸锂玻璃陶瓷存在增韧效果,能够提高复合材料的断裂韧性。     

氧化磷含量对新型牙科玻璃陶瓷微观结构和强度的影响

目的：分析不同氧化磷含量对新型牙科二硅酸锂玻璃陶瓷微观结构和强度的影响。方法：通过调控Li2O、SiO2、K2O、Al2O3、ZrO2-P2O5玻璃系统中氧化磷（P2O5）的含量（0.5%,1.0%,1.5%和2.0%）,并进行相应的热处理,应用X射线衍射技术（XRD）,电子扫描显微术（SEM）分析制备的各组玻璃陶瓷的微观形貌,根据ISO6872标准测试玻璃陶瓷的弯曲强度,进行统计学分析。结果：各组玻璃陶瓷样本的主晶相均为二硅酸锂（Li2Si2O5）,随着P2O5含量的改变,析出晶体的形貌和分布有显著不同。1.0%组玻璃陶瓷具有最高的弯曲强度值。结论：通过调控P2O5含量,可制备具有高强度和适宜微观形貌的二硅酸锂玻璃陶瓷。     

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。     

离子交换强韧化效应对CAD/CAM二硅酸锂玻璃陶瓷机械性能的影响

目的:探究锂-钠离子交换强韧化效应对CAD/CAM二硅酸锂玻璃陶瓷机械性能的影响.方法:制作50个CAD/CAM二硅酸锂玻璃陶瓷圆片状试件,晶化、打磨及抛光后,用4种不同的熔融硝酸钠离子交换工艺进行处理(n=10),分别检测离子交换前后样品的双轴弯曲强度、维氏硬度和断裂韧性.设置未交换组为空白对照.结果:CAD/CAM...     

一种新型牙科二硅酸锂玻璃陶瓷的制备及性能分析

目的:介绍一种新型牙科二硅酸锂玻璃陶瓷的制备方法,并对其性能进行比较分析。方法:用烧结法二次着色工艺制备A2色新型玻璃陶瓷。对新型玻璃陶瓷和IPS e.max Press瓷块(LT A2、MO1和HO1)的弯曲强度、密度、弹性模量、硬度、断裂韧性、透明度及微观结构进行测量分析。结果:新型玻璃陶瓷除弯曲强度(315 MPa)低于MO瓷块(338 MPa)外(P<0.05),其余各项机械性能均与LT和MO瓷块相近(P>0.05)。新型玻璃陶瓷的透明度TP值(21.2)高于HO瓷块(16.5),但低于LT(27.8)和MO瓷块(27.5)(P<0.05)。新型玻璃陶瓷和IPS e.max Press瓷块的微观结构均表现为棒状的Li2Si2O5晶体交错排列,形成互锁微结构。结论:新型玻璃陶瓷的机械性能和微观结构与IPS e.max Press相近,透明度介于MO和HO瓷块之间,能满足临床要求。     

一种新型牙科二硅酸锂玻璃陶瓷的微观结构分析

目的:分析牙科二硅酸锂玻璃陶瓷的微观结构,探讨其可能的自增韧机制。方法:使用X射线衍射仪分析一种新型二硅酸锂玻璃陶瓷及IPS e.max Press LT和MO瓷块的物相组成,并使用扫描电镜观察其表面特征和裂纹扩展方式。结果:3种玻璃陶瓷的主晶相均为Li2Si2O5,次晶相均为Li2SiO3和Li3PO4。Li2Si2O5晶体均呈棒状,交错排列,形成互锁微结构。新型玻璃陶瓷的晶体尺寸大于LT和MO瓷块,其表面孔隙缺陷较后两者少而深。裂纹在这3种玻璃陶瓷中主要沿着晶体间较薄弱的玻璃相扩展。结论:新型玻璃陶瓷与IPS e.max Press LT和MO瓷块的微观结构相似,长棒状的Li2Si2O5晶体所形成的互锁微结构,以及内部的残余应力可对其起到增强增韧的作用。     

IPS-Empress 2玻璃陶瓷不同表面增韧处理的研究

目的:研究不同表面处理方法对IPS-Empress2玻璃陶瓷断裂韧性的影响.方法:模拟口腔潮湿的环境下,对IPS-Empress2玻璃陶瓷进行抛光、上釉、离子交换不同表面处理,采用压痕法(IM)求得不同表面处理后材料的断裂韧性,通过扫描电镜现察不同表面处理后陶瓷表面形态结构;采用X射线衍射仪对材料晶相改变进行定性分析;采用能谱分析仪对材料元素含量改变进行定量分析.结果:不同处理方法与对照组之间有高度统计学意义(P＜0.01);不同处理组间比较,上釉组与抛光组比较差异无显著性(P＞0.05);离子交换组与抛光组,上釉组比较差异有显著性(P＜0.05).结论:表面离子交换增强技术能显著增加IPS-Empress2玻璃陶瓷断裂韧性.其增强效果均优于表面抛光和上釉.表面离子交换组处理后陶瓷材料内部晶体含量增加,表面Na 被K 置换.     

一种通用粘接剂对不同CAD/CAM可切削材料的短期粘接成绩

[摘要] 目的 评估一种通用粘接剂对于三种不同类型的CAD/CAM可切削材料的短期粘接成绩。方法 制作氧化钇稳定四方相氧化锆陶瓷,纳米复合陶瓷和二硅酸锂玻璃陶瓷试件各20枚,其中前两者进行喷砂处理,后者进行HF酸蚀处理。各组陶瓷再分为2亚组,分别使用（SBU）或不使用（Ctr）通用粘接剂Single Bond Universal。以上表面处理瓷片与复合树脂柱通过树脂水门汀粘接,制作粘接试件,37℃水储24ｈ后测试剪切粘接强度并记录断裂模式。喷砂处理的氧化锆陶瓷和纳米复合陶瓷,以及酸蚀处理的二硅酸锂玻璃陶瓷通过扫描电镜（SEM）观察表面微观形态。结果SEM观察显示酸蚀处理的二硅酸锂玻璃陶瓷,喷砂处理的氧化锆陶瓷和纳米复合陶瓷相对于粗化处理前呈现出粗糙的表面形态。三种经粗化处理的材料使用通用粘接剂表面处理后,剪切强度较未使用者显著增强。结论 通用粘接剂Single Bond Universal能够增强氧化钇稳定四方相氧化锆陶瓷,纳米复合陶瓷和二硅酸锂玻璃陶瓷三种类型CAD/CAM可切削材料的短期粘接强度。     

三种二硅酸锂玻璃陶瓷冠抗折强度研究

目的    通过抗折破坏实验分析3种牙科二硅酸锂玻璃陶瓷抗折强度的差异,为国产二硅酸锂玻璃陶瓷临床应用提供依据。方法    将30个下颌第一磨牙标准预备体代型随机分为3组,每组10个,分别制作国产二硅酸锂玻璃陶瓷冠试件（DID组）、IPS e.max CAD冠试件（IPC组）和IPS e.max Press冠试件（IPP组）。3组全瓷冠试件粘接后,分别放置于电子万能试验机上,用直径6 mm圆形加载头,以0.5 mm/min速度垂直加载于全瓷冠面中央至瓷层碎裂,记录最大载荷,即二硅酸锂玻璃陶瓷冠抗折强度。用扫描电镜（SEM）观察表面形态。采用SPSS21.0 统计软件对3组全瓷冠试件抗折强度值进行单因素方差分析和组间两两比较的q检验,检验水准取双侧α = 0.05。结果    3组全瓷冠试件抗折强度结果：DID组为（949.7 ± 119. 4）N,IPC组为（1746.9 ± 244.8）N,IPP组为（2161.8 ± 239.0）N 。3组间总的比较,差异有统计学意义（F = 86.685,P < 0.05）;各组间两两比较,差异亦均有统计学意义（均P < 0.05）。3组全瓷冠试件的断裂模式无显著差异,大部分试件断裂类型均为Ⅰ型。SEM观察,DID组可见晶体在样本中分布不均匀,大小不一,表面有细小裂隙;IPC组可见析出晶体在样本中分布较均匀,晶体较为长大;IPP组可见析出的棒状二硅酸锂晶体均匀分布于玻璃相中,互相嵌合,并形成一种互锁微结构。结论    研究条件下,不同二硅酸锂玻璃陶瓷对抗折强度及断裂类型均有影响,国产二硅酸锂玻璃陶瓷可以满足临床要求,对于其在临床应用有一定指导意义。     

二次熔融烧结法制备牙科用可切削云母基玻璃陶瓷

目的:通过二次熔融烧结法制备以云母为主晶相的牙科用可切削玻璃陶瓷。方法:在1500℃下熔融K2O-MgO-Al2O3-SiO2-F系统基础玻璃,其玻璃粉经过冷等静压成型后无压烧结获得牙科用可切削玻璃陶瓷。采用DTA-TGA确定基础玻璃的核化和晶化温度,采用XRD和SEM分析烧结体的物相组成和微观形貌,以及采用三点弯曲法和压痕法测定烧结体的力学性能。结果:K2O-MgO-Al2O3-SiO2-F系统的核化温度和晶化温度分别选择680℃和1020℃。烧结体的整体析晶比较缓慢,结晶度约为35.48%,主晶相为氟硅云母,晶体呈立方或扁平状,交错排列。烧结体的弯曲强度和断裂韧性分别为(144.50±9.75)MPa和(1.25±0.26)MPa.m1/2。结论:二次熔融烧结法制备的云母基玻璃陶瓷能够满足临床牙体缺损修复的要求。     

Effect of Surface Acid Etching on the Biaxial Flexural Strength of Two Hot-Pressed Glass Ceramics

Purpose: The purpose of this study was to assess the effect of surface acid etching on the biaxial flexural strength of two hot-pressed glass ceramics reinforced by leucite or lithium disilicate crystals.
Materials and Methods: Forty glass ceramic disks (14-mm diameter, 2-mm thick) consisting of 20 leucite-based ceramic disks (IPS Empress®) and 20 lithia disilicate-based ceramic (IPS Empress 2®) were produced by hot-pressing technique. All specimens were polished and then cleaned ultrasonically in distilled water. Ten specimens of each ceramic group were then etched with 9% hydrofluoric (HF) acid gel for 2 minutes and cleaned ultrasonically again. The biaxial flexural strength was measured by the piston-on-three-ball test in a universal testing machine. Data based on ten specimens in each group were analyzed by two-way ANOVA  (α= 0.05)  . Microstructure of ceramic surfaces before and after acid etching was also examined by a scanning electron microscope.
Results: The mean biaxial flexural strength values for each group tested were (in MPa): nonetched IPS Empress = 118.6 ± 25.5; etched IPS Empress = 102.9 ± 15.4; nonetched IPS Empress 2 = 283.0 ± 48.5; and etched IPS Empress 2 = 250.6 ± 34.6. The results showed that the etching process reduced the biaxial flexural strengths significantly for both ceramic types ( p = 0.025). No significant interaction between the ceramic type and etching process was found ( p = 0.407).
Conclusion: From the results, it was concluded that surface HF acid etching could have a weakening effect on hot-pressed leucite or lithia disilicate-based glass ceramic systems.     

Strength and microstructure of IPS Empress 2 glass-ceramic after different treatments

PURPOSE: This investigation was designed to determine whether heat pressing and/or simulated heat treatments affect the flexure strength and microstructure of the lithium disilicate glass-ceramic of the IPS Empress 2 system. MATERIALS AND METHODS: Four groups of the lithium disilicate glass-ceramic were prepared as follows: group 1 = as-received material; group 2 = heat-pressed material; group 3 = heat-pressed and stimulated initial heat-treated material; and group 4 = heat-pressed and simulated heat-treated material with full firings for a final restoration. Three-point bending tests and scanning electron microscopy (SEM) analysis were conducted. RESULTS: The flexure strength of group 2 was significantly higher than that of group 1. However, there were no significant differences in strength among groups 2, 3, and 4, or between groups 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed a closely packed, multidirectionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals in the glass matrix of the heat-pressed materials (groups 2, 3, and 4) were a little more homogeneous and about 2 times bigger than those of the as-received material (group 1). These changes of the microstructure were greatest between groups 1 and 2. However, there were no marked differences among groups 2, 3, and 4. CONCLUSION: Although there were significant increases in the strength and some changes of the microstructure after the heat-pressing operation, the combination of heat pressing and simulated subsequent heat treatments did not produce an increase of strength of IPS Empress 2 glass-ceramic.     

Biaxial flexural strength,elastic moduli,and x-ray diffraction characterization of three pressable all-ceramic materials

STATEMENT OF PROBLEM: Before the release of an advanced ceramic material, independent assessment of its strength, elastic modulus, and phase composition is necessary for comparison with peer materials. PURPOSE: This study compared the biaxial flexural strength, elastic moduli, and crystalline phases of IPS Empress and Empress 2 with a new experimental ceramic. MATERIAL AND METHODS: Twenty standardized disc specimens (14 x 1.1 mm) per material were used to measure the biaxial strength. With a universal testing machine, each specimen was supported on 3 balls and loaded with a piston at a crosshead speed of 0.5 mm/min until fracture. Three standardized bars (30 x 12.75 x 1.1 mm) for each material were prepared and excited with an impulse tool. The resonant frequencies (Hz) of the bars were used to calculate the elastic moduli with the equation suggested by the standard ASTM (C 1259-94). X-ray diffraction with Cu Kalpha at a diffraction angle from 20 to 40 degrees was used to identify the crystalline phases by means of a diffractometer attached to computer software. The data were analyzed with 1-way analysis of variance followed by pairwise t tests (P<.05). RESULTS: Mean biaxial strengths were 175 +/- 32, 407 +/- 45, and 440 +/- 55 MPa for IPS Empress, Empress 2, and the experimental ceramic, respectively. Elastic modulus results were 65, 103, and 91 GPa for the same materials, respectively. There was no significant difference in strength and elastic modulus between Empress 2 and the experimental ceramic. Both materials demonstrated a significantly higher elastic modulus and strength than IPS Empress. X-ray diffraction revealed leucite as the main crystalline phase for IPS Empress and lithium disilicate for both Empress 2 and the experimental ceramic. CONCLUSION: Within the limitations of this study, the improved mechanical properties of Empress 2 and experimental ceramic over those of IPS Empress were attributed to the nature and amount of their crystalline content lithium disilicate.     

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.     

The effect of core material, veneering porcelain, and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics

Purpose: The objective of this study was to compare the effect of veneering porcelain (monolithic or bilayer specimens) and core fabrication technique (heat‐pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite‐reinforced and lithium‐disilicate glass ceramics. In addition, the effect of veneering technique (heat‐pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering porcelain with a powder/liquid layering technique (subgroup 0.8C‐0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat‐pressed veneering porcelain (subgroup 0.8C‐0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C‐0.7VL, 0.8C‐0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C‐0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C‐0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C‐0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C‐0.7VP subgroup. Conclusions: The present study suggests that veneering porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite‐reinforced glass‐ceramic cores have lower flexural strength than lithium‐disilicate ones, while fabrication techniques (heat‐pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat‐pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia‐veneered ceramics exhibited greater flexural strength than monolithic leucite‐reinforced and lithium‐disilicate ceramics regardless of zirconia veneering techniques (heat‐pressed or powder/liquid technique).     

Fracture behavior of lithia disilicate- and leucite-based ceramics

OBJECTIVE: This study was designed to characterize the fracture behavior of ceramics and test the hypothesis that variation in strength is associated with a variation in fracture toughness. METHODS: The following four groups of 20 bar specimens (25 x 4 x 1.2 mm) were fabricated (ISO standard 6872): E1, a hot-pressed leucite-based core ceramic (IPS Empress); E2, a hot-pressed lithia-based core ceramic (IPS Empress 2); ES, a hot-pressed lithia-based core ceramic (Experimental); and GV, a glass veneer (IPS Empress2 body). Specimens were subjected to four-point flexure loading in 37 degrees C distilled water. Fractographic analysis was performed to determine the fracture origin (c) for calculation of fracture toughness (KIC). Weibull analysis of flexure strength (sigma) data was also performed. RESULTS: Differences in mean sigma and KIC were statistically significant for E1 and GV (p<0.05). These differences are associated with processing effects and composition. SIGNIFICANCE: The higher mean sigma and KIC values of E2 and ES core ceramics suggest potentially improved structural performance compared with E1 although the Weibull moduli of E1 and E2 are the same.     

Fracture toughness and hardness evaluation of three pressable all-ceramic dental materials

OBJECTIVES: This study evaluates the fracture toughness and hardness of three pressable all-ceramic materials: IPS-Empress, Empress 2 and an experimental ceramic material. METHODS: Fifteen discs and 15 bars per material were prepared. Fracture toughness was measured with two different techniques: indentation fracture and indentation strength. During the indentation fracture tests the hardness of each material was also measured. Statistical significance among groups of population was studied using one-way Anova and Tukey's multiple comparison tests. RESULTS: Fracture toughness results using the indentation strength technique (with three-point bending and biaxial flexure tests) were: IPS-Empress (1.39 (SD 0.3) and 1.32 (SD 0.3)); Empress 2 (3.14 (SD 0.5) and 2.50 (SD 0.3)) MPa x m(1/2); and the experimental ceramic (3.32 (SD 0.6) and 2.43 (SD 0.3)) MPa x m(1/2). The indentation fracture technique generated orthogonal cracks of different lengths for Empress 2 and the experimental ceramic, whether perpendicular or parallel to the lithium disilicate elongated crystals. Thus, two values were reported: Empress 2 (1.5 (SD 0.2) and 1.16 (SD 0.2)) MPa x am(1/2) and the experimental ceramic (1.67 (SD 0.3) and 1.15 (SD 0.15)) MPa x m(1/2). The IPS-Empress indentation fracture result was 1.26 (SD 0.1). The hardness results were: 6.6, 5.3 and 5.5 GPa for IPS-Empress, Empress 2 and the experimental ceramic, respectively. CONCLUSIONS: No significant differences in fracture toughness and hardness results were found between Empress 2 and the experimental ceramic (P>0.05 ANOVA). Both materials exhibited fracture toughness anisotropy following pressing. They demonstrated improved fracture toughness and reduced hardness compared with IPS-Empress P<0.05(ANOVA), which should be beneficial for clinical applications.     

Crack-healing during two-stage crystallization of biomedical lithium (di)silicate glass-ceramics

ObjectiveThe study is aimed to evaluate the two single commercially available two-step lithium-(di)silicate systems by analyzing their parent glass composition and studying the quantitative crystalline and glass phase evolution during the second stage heat-treatment. The mechanical repercussions of the crystallization firing were evaluated using strength and fracture toughness tests.MethodsXRF and ICP-OES were used to determine the oxide composition of the parent glasses in Suprinity PC (Vita Zahnfabrik) and IPS e.max CAD (Ivoclar-Vivadent). The crystalline phase of both materials was determined by quantitative XRD and the G-factor method in the partially and post-crystallization states. The oxide composition of the residual glass phase was derived by subtracting the chemistry of the crystalline phase fractions from the parent glass composition. Mechanical testing of biaxial flexural strength and fracture toughness were used to demonstrate how crack-like defects behave during crystallization.ResultsThe two tested lithium (di)silicate systems showed strong differences in oxide composition of the parent glass. This showed to influence the transformation of lithium metasilicate in lithium disilicate, with the former remaining in high vol.% fraction in the post-crystallization Suprinity PC. In IPS e.max CAD cristobalite precipitated at the surface during the second-heat treatment. Strength and fracture toughness tests revealed that crack in both materials, whether introduced by grinding or indentation, heal during the crystallization firing. Cristobalite seemed to have contributed to a surface strengthening effect in IPS e.max CAD.SignificanceAccurate crystalline phase quantification aids in the determination of the residual glass composition in dental glass-ceramics. For both systems crystallization firing induced healing of cracks generated by CAM grinding.     

A comparison of fracture strength of yttrium-oxide- partially-stabilized zirconia ceramic crowns with varying core thickness, shapes and veneer ceramics

The fracture strengths of stylized all-ceramic crowns manufactured using an yttrium-oxide-partially-stabilized (Y-TZP) zirconia ceramic core (Denzir) veneered with lithium disilicate glass-ceramics (IPS Empress 2 or IPS Eris) were evaluated. The Denzir cores were manufactured in two ways: either with different thickness in different parts of the restoration, called an 'adapted Denzir core'; or with a uniform core thickness of 0.5 mm. IPS Empress 2 all-ceramic crowns served as reference. There was no significant difference between the crowns with an 'adapted Denzir core' veneered with the two brands of glass-ceramics. No significant difference was seen between the crowns with a 0.5 mm Denzir core veneered with the two brands of glass-ceramics. The crowns with an 'adapted Denzir core' exhibited significantly higher values than those with a 0.5 mm Denzir core and than the IPS Empress 2 crowns used as reference. No significant differences were seen among the IPS Empress 2 crowns used as reference and the crowns with a 0.5 mm Denzir core. The mode of failure varied among the Empress 2 crowns and the crowns with a core of a Y-TZP zirconia ceramic. Long-term studies are necessary to assess the clinical performance of this restorative system.