INVESTIGATIONS ON THE FORMATION OF INITIAL CRACKS IN THERMAL BARRIER COATINGS PREPARED BY EB－PVD

This paper deals with the mechanism of the formation of initial cracks in the yttria partially stabilized zirconia thermal barrier coatings prepared by EB-PVD method.The microcracks were only recognized inside the ceramic top coat of the thermalcycled TBCs. SEM/EDS observations indicated that some special oxides exist in the area just below the cracks.It seems that the formation of the initial cracks can result from the oxidation stress as well as the thermal stress.

^(99m)Tc in the evaluation of microleakage of composite resin restorations with SonicFill^(TM).An in vitro experimental model

Introduction: The composite SonicFillTM (Kerr/Kavo) is indicated for posterior restorations, with a single increment up to 5 mm due to reduced polymerization shrinkage, thus reducing working time. Aim: Evaluation of marginal microleakage with SonicFillTM. Method and Materials: There were sectioned sixty noncarious human molars in the occluso-cervical direction. Class V cavities were prepared on each tooth with gingival margin walls in a standardized way. The specimens were divided into 4 groups: group 1—restored with SonicFillTM (Kerr/Kavo), group 2—restored with FiltekTM SupremeXTE (3M ESPE), group 3—the cavities were not restored;group 4—restored with SonicFillTM (Kerr/Kavo). In groups 1, 2 and 4 the enamel was conditioned with 37% orthophosphoric acid and applied the self-etch adhesive system Clear- fillTM SE BOND (Kuraray). The specimens were stored in distilled water at 37?C for 7 days. After, the specimens, were immersed in a solution of 99mTc-Pertechnetate and the radioactivity was assessed with a gamma camera. The nonparametric Kruskal-Wallis and Mann-Whitney test with Bonferroni correction at a significance level of 5% were used for the statistical analyses. Results: There are significant differences between the positive and negative control groups and between these and experimental groups (p TM and FiltekTM SupremeXTE. Conclusion: The new composite SonicFillTM and FiltekTM SupremeXTE showed no difference concerning dye penetration. The Sonic- FillTM restorative system showed no influence in concerning microleakage.

Effect of Thermocycle Aging on Color Stability of Monolithic Zirconia

Background: The color stability of dental restorative materials is important for long-term clinical success. Objectives: The objective of this study was to examine the effect of thermocycling on the color and translucency stability of monolithic zirconia. Materials and methods: A total of 80 disc-shaped specimens (1 cm diameter) were produced from monolithic zirconia material, Katana High Translucent (Kuraray Noritake Dental, Kurashiki, Japan). The specimens were prepared in four different thicknesses: 0.5 mm, 1 mm, 1.5 mm and 2 mm. Before thermocycling, color measurements of the specimens were made by a spectrophotometer (Spectro Shade TM MICRO;MHT Optic Research AG, Milan, Italy). After the thermal aging procedure, the color measurement was repeated. Data obtained from the study were analyzed with descriptive statistics, correlation analysis, one-way ANOVA and Tukey’s tests. Results: After thermocycling, the L*, a*, b* values decreased at all thicknesses. The maximum change in the L*, a* and b* values was observed in 0.5-mm-thick specimens, while the least change was observed in 2-mm-thick specimens. The amount of color change in the specimens after thermocycling was found to be the highest in 0.5-mm-thick specimens (ΔE = 0.91 ± 0.02), and the lowest in 2-mm-thick specimens (ΔE = 0.85 ± 0.01). While a statistically significant color change (ΔE) was observed in 0.5-mm-thick specimens (p < 0.05), a statistically insignificant color change (ΔE) was observed (p > 0.05) in 1-mm, 1.5-mm, and 2-mm-thick specimens. After thermocycling, the translucency parameter (TP) values decreased at all thicknesses. The highest change in the TP values was observed in 0.5-mm-thickspecimens (1.09 ± 0.03), while the lowest change was observed in 2-mm-thickspecimens (0.40 ± 0.04). While a statistically significant change in the TP values was observed in 0.5-mm-thick specimens (p < 0.05), there was a statistically insignificant change in the TP values of 1-mm, 1.5-mm and 2-mm-thick specimens (p > 0.05). Conclusion: Although the color and translucency values after thermocycling exhibited statistically significant changes in the 0.5 mm thickness group, a statistically significant difference was not observed in the other thickness groups.

模拟空间环境冷热循环作用下TC4合金的微观结构与性能(英文)

本文通过模拟空间环境中冷热循环实验条件,利用光学显微镜、X射线衍射仪、透射电子显微镜及显微硬度仪分析了低地球轨道冷热循环作用下TC4钛合金的微观结构状态和性能的演化行为.实验结果表明,随着循环次数的增加,样品的硬度迅速增加到最大值,在随后的冷热循环过程中样品出现了循环软化现象;冷热循环300次后,α和β相的界面出现大量孔洞,样品中的典型结构转变为尺寸较大的位错胞状亚结构,晶界容易成为应力集中的区域并萌生微裂纹;500次循环样品中的典型结构为位错胞演化而成的亚晶以及晶内的孪晶和割阶结构.本文详细讨论了低地球轨道冷热环境下TC4钛合金微观结构的演变规律和冷热疲劳之间的关系.

Influence of Aging and 2-hydroxyethyl-methacrylate Content on the Color Stability of Experimental 2-hydroxyethyl-methacrylate-added Dental Glass Ionomers

Color stability of dental resin modified glass ionomer （RMGI） has been a challenge to dentistry; therefore, systematic changes in 2-hydroxyethyl methacrylate （HEMA） content were performed experimentally to find an idea to enhance the color stability. Changes in color （△E＊ab） and color coordinates （△L＊, △a＊ and △b＊） of experimental 10-50 wt pct HEMA-added dental glass ionomers （HAGIs） and corresponding RMGIs were determined after 5000 cycles of thermocycling. Color changes of HAGIs were not influenced by the HEMA content while △L＊, △a＊ and △b＊ values were influenced by the HEMA content. Color stability of 30% or 40% HEMA-added HAGIs was not different from those of the commercial RMGIs. Since the influence of HEMA itself on the color stability of HAGIs was limited, compositional modification to increase the color stability of these materials should be developed.