INAUGURAL ARTICLE by a Recently Elected Academy Member:From the Cover: Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

To maximize energy efficiency, gas turbine engines used in airplanes and for power generation operate at very high temperatures, even above the melting point of the metal alloys from which they are comprised. This feat is accomplished in part via the deposition of a multilayer, multicomponent thermal barrier coating (TBC), which lasts up to approximately 40,000 h before failing. Understanding failure mechanisms can aid in designing circumvention strategies. We review results of quantum mechanics calculations used to test hypotheses about impurities that harm TBCs and transition metal (TM) additives that render TBCs more robust. In particular, we discovered a number of roles that Pt and early TMs such as Hf and Y additives play in extending the lifetime of TBCs. Fundamental insight into the nature of the bonding created by such additives and its effect on high-temperature evolution of the TBCs led to design principles that can be used to create materials for even more efficient engines.     

Influence of Veneering Materials on the Marginal Fit and Fracture Resistance of an Alumina Core System

Purpose: This study was undertaken to assess the influence of three‐veneering materials on the marginal fit, fracture resistance, and failure pattern of In‐Ceram alumina crowns. Materials and Methods: Forty In‐Ceram cores were constructed and divided into four groups of ten each. Ten alumina cores were left unveneered, forming the first group for core testing, while the other 30 copings were divided into three groups depending on the veneering material used. The vertical marginal gaps of the alumina copings were measured before and after veneer placement at 16 sites using an optical microscope. The specimens were then loaded to fracture at a crosshead speed of 1 mm/min. Fractured specimens were examined, and the fracture patterns of the crowns were recorded. Selected specimens were examined using scanning electron microscope. Data were presented as means and standard deviation values. One‐way ANOVA was used to compare between mean gap areas and fracture resistance of the three materials. Duncan's post hoc test was used for pairwise comparison between the means when ANOVA test was significant. Results: Vitadur‐N‐veneered crowns showed statistically the highest mean vertical gaps, while no significant difference was evident between the marginal fits of Vitadur‐α‐ and VM7‐veneered crowns. Regarding the strength, a statistically significant decrease in fracture resistance of the cores was evident after veneering with Vitadur‐N; however, no significant change in mean fracture resistance value of Vitadur‐α‐ and VM7‐veneered crowns was evident compared to the alumina cores. VM7‐veneered crowns showed the highest fracture resistance values. Conclusions: Vitadur‐N‐veneered crowns showed the highest mean vertical gaps and the lowest mean fracture resistance values of the tested groups, while VM7‐veneered crowns combined the highest fracture resistance values and clinically acceptable margins. The best interface quality and finest ceramic texture were evident in case of VM7 material.     

Durability of Resin Cement Bond to Aluminium Oxide and Zirconia Ceramics after Air Abrasion and Laser Treatment

Purpose: The erbium laser has been introduced for cutting enamel and dentin and may have an application in the surface modification of high‐strength aluminum oxide and zirconia ceramics. The aim of this study was to evaluate the durability of the bond of conventional dual‐cured resin cements to Procera Al₂O₃ and zirconium oxide ceramics after surface treatment with air abrasion and erbium laser. Materials and Methods: One hundred twenty Al₂O₃ and 120 zirconia specimens measuring 3 × 3 × 0.7 mm³ were divided equally into three groups, and their surfaces treated as follows: either untreated (controls), air abraded with Al₂O₃ particles, or erbium‐laser‐treated at a power setting of 200 mJ. The surface of each specimen was then primed and bonded with one of two dual‐cured resin cements (either SCP‐100 Ceramic Primer and NAC‐100 or Monobond S and Variolink II) using a 1‐mm thick Tygon tube mold with a 0.75‐mm internal bore diameter. After 24 hours and 6 months of water storage at 37°C, a microshear bond strength test was performed at a crosshead speed of 1 mm/min. Surface morphology was examined using a confocal microscope, and failure modes were observed using an optical microscope. The data were analyzed using the Kaplan‐Meier nonparametric survival analysis. Results: In the case of zirconia, air abrasion and Erbium:yttrium‐aluminum‐garnet (Er:YAG) laser treatment of the ceramic surface resulted in a significant reduction in the bond strengths of both resin cements after 6 months water storage; however, when the zirconia surface was left untreated, the SCP‐100/NAC‐100 group did not significantly reduce in bond strength. In the case of alumina, no treatment, air abrasion and Er:YAG laser treatment of the surface led to no significant reduction in the bond strengths of the three SCP‐100/NAC‐100 groups after 6 months water storage, whereas all three Monobond S/Variolink II groups showed a significant reduction. Conclusion: Er:YAG laser treatment of the zirconia surface did not result in a durable resin cement/ceramic bond; however, a durable bond between a conventional dual‐cured resin cement and Procera All Ceram and Procera All Zirkon was formed using a ceramic primer containing the phosphate monomer, MDP, without any additional surface treatment.     

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目的探讨Crystaleye自动比色仪在玻璃渗透氧化铝全瓷冠修复中比色的临床效果。方法选择2009年3月至2010年3月于中国医科大学口腔医学院修复科就诊的前牙玻璃渗透氧化铝全瓷冠修复的患者119例(318颗患牙),随机分为对照组(157颗患牙)和试验组(161颗患牙),分别采用Vitapan 3D比色板和Crystaleye自动比色仪进行比色。修复后,用Crystaleye自动比色仪对各组修复体和比色参照的天然牙进行测色,计算每组修复体与天然牙的总色差(△E)和患者满意率。结果对照组和试验组的△E分别为(2.14±0.66)NBS、(1.78±0.52)NBS,差异有统计学意义(P<0.05)。对照组患者满意率为66.24%,试验组患者满意率为80.12%,差异有统计学意义(P<0.05)。结论使用Crystaleye自动比色仪能更好地指导玻璃渗透氧化铝全瓷冠的颜色复制,提高临床修复效果。     

Influence of contamination on resin bond strength to nano‐structured alumina‐coated zirconia ceramic

Zhang S, Kocjan A, Lehmann F, Kosma? T, Kern M. Influence of contamination on resin bond strength to nano‐structured alumina‐coated zirconia ceramic. Eur J Oral Sci 2010; 118: 396–403. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci The purpose of this study was to evaluate the influence of contamination and subsequent cleaning on the bond strength and durability of an adhesive resin to nano‐structured alumina‐coated zirconia ceramic. Zirconia ceramic disks were coated with nano‐structured alumina, utilizing the hydrolysis of aluminum nitride powder. After immersion in saliva or the use of a silicone disclosing agent, specimens were cleaned with phosphoric acid etching or with tap water rinsing only. Uncontaminated specimens served as controls. Plexiglas tubes filled with composite resin were bonded with a phosphate monomer [10‐methacryloxydecyl‐dihydrogenphosphate (MDP)]‐containing resin (Panavia 21). Subgroups of eight specimens each were stored in distilled water at 37°C, either for 3 d without thermal cycling (TC) or for 150 d with 37,500 thermal cycles from 5 to 55°C. The tensile bond strength (TBS) was determined using a universal testing machine at a crosshead speed of 2 mm min^?1. The topography of the debonded surface was scrutinized for fractographic features, utilizing both optical and scanning electron microscopy. The TBS to uncontaminated nano‐structured alumina‐coated zirconia ceramic was durable, while contamination significantly reduced the TBS. Phosphoric acid cleaning was effective in removal of saliva contamination from the coated bonding surface but was not effective in removal of the silicone disclosing agent. Nano‐structured alumina coating improves resin bonding to zirconia ceramic and eliminates the need for air‐abrasion before bonding.     

不同树脂粘接剂对渗透陶瓷粘接强度的影响

目的观察比较不同树脂粘接剂对氧化铝渗透陶瓷粘接剪切强度的效果。方法选择无龋坏的人离体磨牙40颗,处理后随机分为4组,每组10件。A组用Solobond Plus粘接剂+Bifix QM粘接剂,B组用Fu-turabond DC粘接剂+Bifix QM粘接剂,C组用Bifix SE自酸蚀树脂粘接剂,D组用Panavia F双重聚合型粘接材料。所有样本在37℃蒸馏水中储存24 h后进行测试,记录剪切强度值,用SAS 6.12统计软件对结果进行单因素方差分析。结果 Panavia F双重聚合型粘接材料组的剪切强度显著高于其他3组(P<0.01),Bifix SE自酸蚀树脂粘接剂组的剪切强度最小。结论 Panavia F双重聚合型粘接材料用于氧化铝渗透陶瓷可获得较好的粘接效果,值得在临床上推广。     

Morphological zeta-potential variation of nanoporous anodic alumina layers and cell adherence

Nanoscale surface modification of biomedical implant materials offers enhanced biological activity concerning protein adsorption and cell adherence. Nanoporous anodic alumina oxide (AAO) layers were prepared by electrochemical oxidation of thin Al-seed layers in 0.22 M C₂H₂O₄, applying anodization voltages of 20–60 V. The AAO layers are characterized by a mean pore diameter varying from 15 to 40 nm, a mean pore distance of 40–130 nm, a total porosity of ∼10% and a thickness of 560 ± 40 nm. Zeta potential and isoelectric point (iep) were derived from streaming potential measurements and correlated to the topology variation of the nanoporous AAO layers. With decreasing pore diameter a shift of iep from ∼7.9 (pore diameter 40 nm) to ∼6.7 (pore diameter 15 nm) was observed. Plain alumina layers, however, possess an iep of ∼9. Compared to the plain alumina surface an enhanced adherence and activity of hFOB cells was observed on the nanoporous AAO after 24 h culture with a maximum at a pore size of 40 nm. The topology-induced change of the electrochemical surface state may have a strong impact on protein adsorption as well as on cell adhesion, which offers a high potential for the development of bioactive AAO coatings on various biomaterial substrates.     

Structurally engineered anodic alumina nanotubes as nano-carriers for delivery of anticancer therapeutics

Here, we report a study on the biocompatibility, cell uptake and in vitro delivery of tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) by new nano-carriers called anodic alumina nanotubes (AANTs) for potential cancer therapy. AANTs were electrochemically engineered by a unique pulse anodization process, which enables precise control of the nanotube geometry, and used here as nano-carriers for drug delivery. In vitro cytotoxicity and cell uptake of AANTs was assessed using MDA-MB231-TXSA human breast cancer cells and mouse RAW 264.7 macrophage cells. AANTs exhibited excellent biocompatibility in both cell lines over a time course of five days even at a maximum concentration of AANTs of 100 μg mL⁻¹. Transmission electron microscopy and fluorescence microscopy confirmed a significant uptake of AANTs by RAW 264.7 cells and breast cancer cells. AANTs loaded with the pro-apoptotic protein Apo2L/TRAIL showed exceptional loading capacity (104 ± 14.4 μg mg⁻¹ of AANTs) and demonstrated significant decrease in viability of MDA-MB231-TXSA cancer cells due to apoptosis induction. These results demonstrate that AANTs are promising nano-carriers for drug delivery applications.     

The origin of nucleation and development of porous nanostructure of anodic alumina films

The galvanostatic growth of porous anodic alumina films during the initial transient stages and starting region of steady state was studied by chronopotentiometry, a suitably modelled mass balance method, a high field kinetic model for ions transport in solid oxide and SEM. The results postulate that the nucleation of pores towards the end of the first transient stage results from recrystallization of rare oxide lattice produced in metal|oxide interface, accommodated with Al lattice, to the surface of initially flat film forming nanocrystallites of denser oxide and crack-like holes nuclei of pores between crystallites. During the second transient stage the successive transformation nuclei → pockets → channel-like pores results from simultaneous continuing production of oxide at a slightly declining rate, gradual localization of charge transfer processes from the flat surface to their bottom, recrystallization of oxide in the barrier layer establishing finally a stable gradient of density rising to electrolyte and conversion of barrier layer from flat to close packed shell shaped units accommodating these changes. The enhanced recrystallisation and density rise towards the pore base and wall surface and the necessity for equilibration of stresses inside each barrier layer unit and between neighbouring units yield hemispherical barrier layer units, self-ordering of porous structure approaching the highest possible 2D hexagonal symmetry in finite surface domains and permanent growth of structure in steady state.     

Ion transport in nanocrystalline materials: a computer simulation study

The results of molecular dynamics simulations of ionic transport in nanostructured materials are presented. Two types of materials are considered, the single component nanostructured oxide, sodium β-alumina and the mixed phase composite LiI/Al₂O₃. In nanostructured β-alumina, the conductivity is observed to be considerably lower than in crystalline β-alumina. Blocking grain boundaries between the nanosized grains cause the reduction. In the case of the composite, a crystallite of LiI with (0 0 1) surface planes was sandwiched between α and γ-Al₂O₃, respectively. In both cases Li⁺-ions were observed to transfer from LiI to tetrahedral sites in the Al₂O₃ surface, α-alumina having the higher surface charge density. As a result, a defective region develops near the interface in the LiI and lithium transport along the surface can occur. The ions migrate through vacancy hopping in the defective regions in LiI. The defective region is only two Li⁺-layers thick. When the thickness of the LiI slab becomes comparable with the thickness of the defective region, the LiI becomes more disordered. The activation energy for Li⁺-diffusion decreases, but this is more than compensated for by a reduction in charge carriers.