An improved technique for dental alloy etching with a potentiostatic device

Since a good retention of direct bonded retainers onto abutment teeth is the primary requirement for the fabrication of etched fixed partial dentures, successful formation of a micromechanical retentive architecture on the bonding surface is one of the most important procedures. For creating such a retentive dendritic pattern on nonprecious metal, a 2-electrode electrolytic method has been used. This equipment consists of a low-voltage DC power supply and two electrodes, namely, a working and a counter one. However, the current and voltage should be monitored during the entire processing time and the etching area must be pre-estimated. A potentiostat has been used to automatically stabilize the voltage across the working electrode and reference electrode by adjusting the current, as commonly employed in electro-chemical technology. A 3-electrode corrosion device originally developed for laboratory research was adapted for dental retainer etching in this study. The results revealed that the etching of dental nonprecious metal (Ni-Cr-Be alloy) could successfully be performed by using the system with a potentiostat. Moreover, the working potential was found to be approximately 1.3 volts by taking the midpoint between the breakdown and the critical potentials for passivation on the potentiostatic anode polarization curves. The optimal exposure time has been found to be in a range of 3 to 5 minutes and 4 minutes to be ideal as determined by SEM microphotographic observation which showed a uniform dendritic pattern with regular lattice form of alternating ridges and valleys.(ABSTRACT TRUNCATED AT 250 WORDS)     

Shear bond strength between different materials bonded with two resin cements

doi: 10.1111/j.1741‐2358.2011.00565.x
Shear bond strength between different materials bonded with two resin cements Background: The aim of this study was to compare the shear bond strength between Ni–Cr alloy specimens bonded to air‐abraded Ni–Cr, bur‐abraded Ni–Cr, etched ceramic and etched enamel substrates using the resin cements RelyX ARC or Enforce. Materials and methods: Ni–Cr specimens were made and sandblasted with Al₂O₃ airborne‐particles. Disc‐shaped patterns were made for each of the four experimental substrates: Ni–Cr treated with Al₂O₃ airborne‐particles, Ni–Cr treated with diamond bur abrasion, etched enamel and etched ceramic. Results: Significant differences in shear bond strength were found between the different materials and luting agents evaluated. The Ni–Cr alloy cylinders bonded to Ni–Cr surfaces sandblasted with 50 μm Al₂O₃ particles and bonded with Enforce achieved the highest bond strength when compared with other substrates (28.9 MPa, p < 0.05). Bur‐abraded metal discs had lowest values, regardless the cement used (2.9 and 6.9 MPa for RelyX and Enforce, respectively). Etched enamel and etched ceramic had similar shear bond strengths within cement groups and performed better when RelyX was used. Conclusions: Bonding Ni–Cr to Ni–Cr and ceramic may result in similar and higher bond strength when compared to Ni–Cr/enamel bonding. For metal/metal bonding, higher shear bond strength was achieved with resin cement Enforce, and for metal/ceramic and metal/enamel bonding, RelyX had higher results.     

Building Interfacial Nanostructures by Size-Controlled Chemical Etching

Development of soft chemical processes for the synthesis of interfacial architectures with well-defined structural nano-motifs organized over large areas in two dimensions is an important branch of nanotechnology. The present study deals with the fabrication of gold nanostructures using size-selective chemical etching of continuous gold films on glass support with titanium and chromium adhesive layers. In this process, which is called self-passivated surface etching, a gold film is etched in the presence of citric acid, resulting in gold nanostructures adhering to the metal support. The size-controlled chemical dissolution of gold is driven by a competing reaction between self-organized passivation of surface nano-motifs by citric acid shells and soft etching by a nonoxidative composition containing hydrochloric acid and hydrogen peroxide in water. According to these results, the presence of a chemically stable adhesive layer (titanium), citric acid in solution, and agitation are critical factors to be considered. However, the nature of the adhesive layer is the most influential factor. The following technique presents a simple method for the rapid fabrication of a nanostructured gold substrate that has the ability to support both propagating and localized surface plasmon resonances simultaneously.     

The effect of oxygen and humidity on charged particle registration in organic foils

The number and diameter of microscopically visible alpha-particle tracks which can be etched in the surface of sensitive plastic foils such as cellulose triacetate are increased by the presence of oxygen. Pre- or posttreatment of foils with water or humid air increases the etching speed but not the foils' sensitivity. Treatment of foils with diluted H202 increases the sensitivity slightly, but the etching speed considerably. Some parameters of the oxygen/humidity effect are described; its possible consequences for the interpretation of the latent track formation process and its practical applications are discussed briefly.     

Running wheel choice by Syrian hamsters

The present study investigated the preference of male and female Syrian hamsters, Mesocricetus auratus, for different types of running wheels. Hamsters were placed individually in sets of multiple cages linked by tunnels, each cage with a different running wheel. The number of wheel revolutions in each cage was tallied daily over 40 days. The hamsters did not express a preference when offered a choice of a running surface made of metal rods spaced 9 mm apart and a similar running surface covered in plastic mesh to prevent the possible slippage of feet between the rods. The hamsters did express a clear preference for larger wheels (35 versus 23 cm diameter), and for completely circular wheels over truncated ones. They neither favoured nor rejected wheels with small obstacles along the running surface. In all experiments, preferences were more strongly expressed by males than by females. Running wheels for hamsters may be improved by enlarging their diameter (to the standards often used for rats, if practically possible) and by ensuring good footing on the running surface (a space no larger than 9 mm between evenly spaced rods seems sufficient to achieve this, at least in large wheels and for hamsters older than 55 days). Installing obstacles along the running surface does not appear to make the wheel more interesting to hamsters.     

预酸蚀乳牙牙本质对自酸蚀粘接系统粘接强度的影响

目的:探讨预酸蚀乳牙牙本质对自酸蚀粘接系统粘接强度的影响。方法:随机选取28颗健康乳磨牙,磨除颊舌面釉质,暴露牙本质粘接面,沿近远中向劈开形成56个样本,随机分为7组(n=8)。直接涂布组(A1组,A2组和A3组)分别涂布AdperTM Easy One(AEO),Xeno-V(XV)和OptiBond All In One(AIO)三种自酸蚀粘接剂,预酸蚀组(B1组,B2组和B3组)在涂布三种自酸蚀粘接剂前先使用35%磷酸酸蚀乳牙牙本质15 s,对照组(C组)使用Prime&Bond NTTM(NT)全酸蚀粘接剂,每个样本用Z350复合树脂堆砌成直径为3 mm的树脂小柱,通过剪切试验测试剪切粘接强度,并通过扫描电子显微镜观察断裂表面形态。结果:B1组,B2组的剪切粘接强度值明显高于A1组,A2组(P<0.001);B3组与A3组的剪切粘接强度值比较无明显差别(P=0.94)。A2组的剪切粘接强度值低于C组(P<0.05);B1组的剪切粘接强度值明显高于C组(P<0.001)。扫描电镜观察结果显示各组试件断裂面形态多为牙本质和复合树脂界面破坏。直接涂布组(A1组,A2组和A3组)断裂多发生在混合层的底部,树脂突较少且低于小管口。B1组和B2组试件断裂面可见多数牙本质小管被树脂突填满,断裂多发生在混合层的中上部。B3组试件断裂面可见牙本质小管空虚,树脂突较少。结论:预酸蚀乳牙牙本质可以提高AEO,XV两种自酸蚀粘接剂的剪切粘接强度。自酸蚀粘接剂处理乳牙牙本质可以达到全酸蚀粘接剂处理的粘接强度,但应用自酸蚀粘接剂前预酸蚀乳牙牙本质可以获得更高的粘接强度。     

RECONSTRUCTION OF THE FEEDING APPARATUS IN PLOEOTIA COSTATA (EUGLENOPHYTA) AND ITS RELATIONSHIP TO OTHER EUGLENOID FEEDING APPARATUSES

The ultrastructure of the feeding apparatus in Ploeotia costata Farmer and Triemer was determined and compared to other euglenoid feeding apparatuses. The feeding apparatus opened subapically onto the ventral surface and extended nearly the entire length of the cell. It consisted of four parts at the anterior surface: a comb, cytostome/pocket, vanes, and supporting rods. The comb was a multilayered structure of three horizontal microtubular rows encased in cement and formed the dorsal lip of the apparatus. The cytostome/pocket was located between the comb and the supporting rods, tapered into the cell as the cytopharynx and was surrounded by five vanes. The electron-opaque vanes extended the entire length of the feeding apparatus and were lined with microtubules for most of their length. Finally, two cement supporting rods that were joined by a crosspiece at the anterior end formed the ventral lip. The rods separated briefly before merging with the vanes. As the merged rods and vanes descended into the cell, they gradually narrowed and terminated. Comparisons of the feeding apparatus with Ploeotia vitrea, Diplonema ambulator, Lentomonas applanatum, and other euglenoids have led to the conclusion that the Type II feeding apparatus is found only in Ploeotia species.     

Multifunctional coating films by layer-by-layer deposition of cellulose and chitin nanofibrils

An environmentally benign surface modification process for plastic films was demonstrated by fabricating composite coatings through layer-by-layer assembly with green solid materials: aqueous dispersions of two kinds of crystalline polysaccharide nanofibrils. Anionic cellulose nanofibrils were obtained by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation of native cellulose, while cationic β-chitin nanofibrils were prepared by the protonation of squid pen chitin. Uniform layer depositions, driven by electrostatic attraction and enhanced by hydrogen bonding, were observed on silicon wafers and then reproduced onto poly(ethylene terephthalate) films. Contact angle measurements and dyeing tests on the resulting films revealed their hydrophilic nature and the sorption of both charged and uncharged substances. Antireflection properties were also confirmed via the light transmittance measurements. As might be presumed from all these properties, this composite coating exhibited its unique behavior largely due to its structure, which was distinct from both those of nanofibril cast films and polymer films.     

Mechanical Expansion of Steel Tubing as a Solution to Leaky Wellbores

Wellbore cement, a procedural component of wellbore completion operations, primarily provides zonal isolation and mechanical support of the metal pipe (casing), and protects metal components from corrosive fluids. These are essential for uncompromised wellbore integrity. Cements can undergo multiple forms of failure, such as debonding at the cement/rock and cement/metal interfaces, fracturing, and defects within the cement matrix. Failures and defects within the cement will ultimately lead to fluid migration, resulting in inter-zonal fluid migration and premature well abandonment. Currently, there are over 1.8 million operating wells worldwide and over one third of these wells have leak related problems defined as Sustained Casing Pressure (SCP)¹. The focus of this research was to develop an experimental setup at bench-scale to explore the effect of mechanical manipulation of wellbore casing-cement composite samples as a potential technology for the remediation of gas leaks. The experimental methodology utilized in this study enabled formation of an impermeable seal at the pipe/cement interface in a simulated wellbore system. Successful nitrogen gas flow-through measurements demonstrated that an existing microannulus was sealed at laboratory experimental conditions and fluid flow prevented by mechanical manipulation of the metal/cement composite sample. Furthermore, this methodology can be applied not only for the remediation of leaky wellbores, but also in plugging and abandonment procedures as well as wellbore completions technology, and potentially preventing negative impacts of wellbores on subsurface and surface environments.     

Control of Glass–Metal Composite Optical Nonlinearity via Nanostructuring

We perform theoretical study of the nonlinear transmission and nonlinear diffraction in nanogratings etched at the surface of copper- and silver-based glass–metal composites. By assuming low metal concentration in the glass matrix, we employ Maxwell Garnett approach to obtain refractive index and absorption coefficient, while the optical nonlinearity of the composite is described using anharmonic oscillator model. We demonstrate that both nonlinear refraction and nonlinear absorption contribute to the light-induced transmittance of the nanostructured slab of the copper-based composite. In particular, in contrast to the silver-based composite, the nonlinear refraction modifies considerably the wavelength dependence of the light-induced transmission change in the copper copper-based composite.

     

Wild capuchins (Cebus capucinus) fail to use tools in an experimental field study

From September through November 2000 we conducted an experimental field study of tool use in a group of 15 wild white-faced capuchins (Cebus capucinus) in Costa Rica. The problem presented to the capuchins involved the use of wooden dowels as probes to obtain a food reward (two bananas) located inside a clear Plexiglas box. Specifically, the task required the capuchins to manually insert a dowel into any of six holes drilled into the box in order to push the bananas off a shelf. The banana could then be retrieved through a large opening at the bottom of the box. The capuchins visited the tool-use platform 702 times over the course of 55 consecutive days and under several experimental conditions. During the first 21 days of the study, they explored the box but made no attempt to touch or pick up the dowels. Even after we placed the dowels in the holes, the capuchins only occasionally manipulated them. Overall, the results indicate that the capuchins did not use a tool to solve this novel foraging problem.     

Bilayer reconstitution of voltage-dependent ion channels using a microfabricated silicon chip

Painted bilayers containing reconstituted ion channels serve as a well defined model system for electrophysiological investigations of channel structure and function. Horizontally oriented bilayers with easy solution access to both sides were obtained by painting a phospholipid:decane mixture across a cylindrical pore etched into a 200-microm thick silicon wafer. Silanization of the SiO(2) layer produced a hydrophobic surface that promoted the adhesion of the lipid mixture. Standard lithographic techniques and anisotropic deep-reactive ion etching were used to create pores with diameters from 50 to 200 microm. The cylindrical structure of the pore in the partition and the surface treatment resulted in stable bilayers. These were used to reconstitute Maxi K channels in the 100- and 200-microm diameter pores. The electrophysiological characteristics of bilayers suspended in microchips were comparable with that of other bilayer preparations. The horizontal orientation and good voltage clamping properties make the microchip bilayer method an excellent system to study the electrical properties of reconstituted membrane proteins simultaneously with optical probes.     

Er,Cr:YSGG激光切割对牙体与充填物粘结力影响的研究

本文用 1千牛电液疲劳实验机检测充填材料与牙面之间的粘结力 ,发现 :在牙釉质组中 ,酸蚀组、6瓦激光切割组及 6瓦激光切割联合酸蚀组抗剪切粘结强度无显著性差异 (P >0 .0 5) ;在牙本质组中 ,酸蚀组、4瓦激光切割组及 4瓦激光切割联合酸蚀组抗剪切粘结强度也无显著性差异 (P >0 .0 5)。并通过SEM观察激光处理后牙体表面结构的变化 ,发现激光切割后牙釉质表面不平呈层状 ,无玷污层 ,釉柱未见破坏 ;牙本质小管开放 ,表面无玷污层 ,达到酸蚀的效果。因此Er,Cr :YSGG激光切割牙体硬组织具有传统钻切割与酸蚀刻的联合作用 ,可以代替传统的酸蚀方法。     

Experimental field study of problem-solving using tools in free-ranging capuchins (Sapajus nigritus, formerly Cebus nigritus)

Some populations of capuchins are reported to use tools to solve foraging problems in the wild. In most cases, this involves the act of pounding and digging. The use of probing tools by wild capuchins is considerably less common. Here we report on the results of an experimental field study conducted in southern Brazil designed to examine the ability of wild black-horned capuchins (Sapajus nigritus) to use a wooden dowel as a lever or a probe to obtain an embedded food reward. A group of eight capuchins was presented with two experimental platforms, each housing a clear Plexiglas box containing two bananas on a shelf and four inserted dowels. Depending on the conditions of the experiment, the capuchins were required either to pull (Condition I) or push (Conditions II and III) the dowels, in order to dislodge the food reward from the shelf so that it could be manually retrieved. In Condition I, four individuals spontaneously solved the foraging problem by pulling the dowels in 25% (72/291) of visits. In Conditions II and III, however, no capuchin successfully pushed the dowels forward to obtain the food reward. During these latter two experimental conditions, the capuchins continued to pull the dowels (41/151 or 27% of visits), even though this behavior did not result in foraging success. The results of these field experiments are consistent with an identical study conducted on wild Cebus capucinus in Costa Rica, and suggest that when using an external object as a probe to solve a foraging problem, individual capuchins were able to rapidly learn an association between the tool and the food reward, but failed to understand exactly how the tool functioned in accomplishing the task. The results also suggest that once a capuchin learned to solve this tool-mediated foraging problem, the individual persisted in using the same solution even in the face of repeated failure (slow rate of learning extinction).     

Effects of Mechanical and Chemical Pretreatments of Zirconia or Fiber Posts on Resin Cement Bonding

The bonding strength between resin cement and posts is important for post and core restorations. An important method of improving the bonding strength is the use of various surface pretreatments of the post. In this study, the surfaces of zirconia (fiber) posts were treated by mechanical and/or chemical methods such as sandblasting and silanization. The bonding strength between the zirconia (fiber) post and the resin cement was measured by a push-out method after thermocycling based on the adhesion to Panavia F 2.0 resin cement. The zirconia and fiber posts exhibited different bonding strengths after sandblasting and/or silanization because of the different strengths and chemical structures. The zirconia post showed a high bonding strength of up to 17.1 MPa after a combined treatment of sandblasting and silanization because of the rough surface and covalent bonds at the interface. This effect was also enhanced by using 1,2-bis(trimethoxysilyl)ethane for the formation of a flexible layer at the interface. In contrast, a high bonding strength of 13.9 MPa was obtained for the fiber post treated by silane agents because the sandblasting treatment resulted in damage to the fiber post, as observed by scanning electron microscopy. The results indicated that the improvement in the bonding strength between the post and the resin cement could be controlled by different chemical and/or mechanical treatments. Enhanced bonding strength depended on covalent bonding and the surface roughness. A zirconia post with high bonding strength could potentially be used for the restoration of teeth in the future.     

Potential for total nitrogen removal by combining vertical flow and horizontal flow constructed wetlands: A full-scale experiment study

To improve total nitrogen removal, a full-scale experimental study was conducted on a hybrid constructed wetlands plant designed for 100 person equivalents. The plant was composed of a first stage of vertical filters (fed with raw wastewater), followed by a second stage of horizontal filters. It was monitored over one year, measuring hydraulic conditions, physico-chemical conditions, gas emission, oxygen levels in the gas phase as well as regular treatment performance by 24-h composite samples. Different vertical filter configurations (media depth, intermediate and passive aeration system) were tested as well as two horizontal filter designs. Nitrogen removal is discussed in terms of the efficiency of each stage in relation to the season and the load applied. This study indicates limits for systems configuration and suggests some design avenues for hybrid systems to reach high and regular levels of nitrogen removal with reasonable surface area per person.     

Micro/nanoscale well and channel fabrication on organic polymer substrates via a combination of photochemical and alkaline hydrolysis etchings

With the utilization of photomasks, micro/nanoscale wells and channels with depths ranging from nanometers to several micrometers were fabricated on a poly(ethylene terephthalate) (PET) surface by a simple combination of photochemical and alkaline hydrolysis etching. The PET surface region could be directly and photochemically etched by UV light and N,N-dimethylformamide (DMF) to create 125-350 nm etching depths (step 1). In step 2, the depth could be further enlarged to 250-1400 nm by potassium hydroxide (KOH) developing. More importantly, when this combination etching was repeated with the same photomask, the depth increased with increasing etching times. For instance, the depth reached approximately 6 microm after a series of three combination etchings. The cross-sectional shape of the final structure was trapezoidal with smooth corners. No obvious widening effect in lateral size was observed after one combination etching, whereas the top width of the microfabricated channels was enlarged from 50 microm (the designed feature of the photomask used) to 100 microm after two or three combination etchings. Even more interesting was that step 1 resulted in the formation of a kind of aminated surface in the channel (6.5% amine content), but when step 2 was conducted, the aminated surface was erased. This process could be reversibly carried out by repeating step 1 (amination) and step 2 (erasing). Electrostatical self-assembly of an antibody, fluorescein isothiocyanate-labeled immunoglobulin G (FITC-IgG, goat anti-rabbit), was achieved on the aminated surface of the etched channels, which demonstrated that by this combination strategy, micro/nanoscale channels or wells featuring tunable depths and functional channel surfaces could be readily fabricated. Undoubtedly, these functionalized channels or wells onto organic substrates could provide a potential platform for microchips toward various functions such as microarrays, heterogeneous immunoassays, biosensors, concentrations, filtrations, and microanalysis.     

Visualization of mitochondrial coupling factor F1(ATPase) by freeze-drying.

It is known that the negatively stained preparations of inner mitochondrial membrane display characteristic approximately 9 nm F1 (ATPase) knobs projecting from the matrix surface. Freeze-etch studies have reported the absence of such knobs from the "etched" surface of the inner mitochondrial membranes. We have demonstrated their presence on the surface of SMP (submitochondrial particles) prepared by freeze-drying for transmission electron microscopy. This identification has been substantiated by comparison with freeze-dried TU particles (trypsin-urea treated SMP) that are devoid of F1 (ATPase). It has been suggested that a layer of water molecules is strongly adsorbed to the surface of SMP and does not sublime during normal freeze-"etching."     

Effect of Support Material on the Development of Microbial Fixed Films Converting Acetic Acid to Methane*

A study of the development of methanogenic fixed films on pieces of polyvinyl chloride plastic, etched glass and baked clay showed that support material markedly affected the rate of attachment and growth of bacteria converting acetic acid to methane. Film development, as indicated by the rate of acetate conversion to methane and carbon dioxide, was threefold faster on fired clay than on either PVC plastic or etched glass. Scanning electron micrographs showed that the film of bacteria attached to clay was thick and uniform, while the film attached to PVC plastic was thin although still uniform. Attachment to etched glass was spotty. The characteristics of clay which made it a superior support appeared to be its rough, porous surface which offered attachment sites to the micro-organisms and the presence of minerals in the clay, particularly iron which is known to stimulate methanogenesis and growth.     

A procedure for SEM of complex shoot structures applied to the inflorescence of snapdragon (Antirrhinum)

Summary An indirect procedure for the scanning electron microscopy of living complex shoot structures, e.g., an inflorescence tip, employs the polymerization of a dental impression plastic. Application of the plastic to exposed surfaces during prolonged dissection minimizes desiccation. The resulting complex mould is everted so that recesses representing surface detail can be filled with molten epoxy polymer. The mould is then allowed to revert to its original configuration; it is now filled with epoxy. After the epoxy hardens, the resulting cast is sputter-coated and imaged. Intricate structures up to 1 mm in dimension can be imaged with all components, e.g., flowers on an inflorescence, in situ.