Biological influence of some crown and bridge restorative materials finished and polished by different techniques

Fixed restorations should satisfy certain biologic requirements and they must not be injurious to the surrounding living tissues as pulp, periodontal ligament, alveolar bone and gingiva. It is best to terminate preparations above the gingival margin but for retention and esthetics considerations the margins of the fixed restorations could be placed subgingivally. In recent years, the biologic effects of dental restorative materials on the gingiva and periodontal tissues have been better appreciated. A rough surface restoration attracts and retains bacterial plaque and irritates the surrounding soft tissues which is injurious to the living supporting structure of the abutments.     

Effect of substrate surface polishing on galvannealing characteristics of a mild IF and an HSIF steel

Abstract

Mechanical properties and visual appearance of galvannealed steel sheets are strongly influenced by steel substrate surfaces before dipping into molten Zn. It has been known that oil contamination, iron fragments and surface enrichment of oxides deteriorate the Fe–Zn reaction and result in various harmful surface defects on the galvannealed coating. In order to prepare the optimal galvannealed coating for automotive exposed panels, the steel substrate surfaces were mechanically polished by SiO₂ polishing brushes.

The types of brush and pressure between the brush roll and strip are major factors for removing the appearance of visual defects on the surfaces of galvannealed coatings. The microstructure of the polished substrate, galvannealed coating and whiteness index on the surface of steel substrate were characterised by optical microscopy, scanning electron microscopy and colour difference meter.     

Magnification characteristics of fundus imaging systems

OBJECTIVE: To compare the magnification properties of 11 different fundus cameras (including 1 stereo fundus camera), a Rodenstock (infrared) scanning laser ophthalmoscope (SLO), the Heidelberg Laser Tomographic Scanner (LTS), and the Heidelberg Retina Tomograph (HRT). DESIGN: A cross-sectional study of the relationship between the true size of a fundus feature and its photographic-computer image in 14 different fundus imaging devices. This relationship was evaluated for each instrument using a model eye adjusted for axial ametropia between +11 diopter (D) and -14 D. To simulate refractive ametropia, the "crystalline lens" was removed to render the model eye aphakic, and the axial length was adjusted to give aphakic ametropia from emmetropia to +20 D. MAIN OUTCOME MEASURES: A correction factor (p) was calculated for each instrument, which can be used in calculations for determining true retinal size. RESULTS: The following were found to be of telecentric construction, Zeiss Oberkochen (WS240 Heidelberg), Zeiss Oberkochen (UK), Zeiss Oberkochen (Cologne), Nikon NF505, Kowa RCXV, SLO prototype (UK), LTS, and the HRT, and each exhibited a constant relationship between p and degree of ametropia of the model eye. The Canon CF6OU, Canon CF6OS, Canon CR4-45NM, Nidek 3-DX, Olympus GRCW, and Carl Zeiss Jena Retinophot were found not to be telecentric and exhibited a linear relationship between p and degree of ametropia of the model eye. For all instruments, p remained unchanged for axial and refractive ametropias of the same degree. CONCLUSIONS: The study has shown that not all fundus imaging systems are telecentric, so the use of a single magnification correction value may not be appropriate. These findings have important implications for the way in which true retinal size calculations are performed. Examples are given to show how the tabulated values of correction factors can be used for both telecentric and nontelecentric cameras in image size calculations.     

Surface topography and frictional characteristics of ceramic brackets

The surface topography and frictional characteristics of single crystal sapphire and polycrystalline alumina brackets were evaluated in both the dry and the wet state as a function of the four basic wire alloy compositions. On the premise that a particular combination of bracket, wire, and environment must be attained so that the efficiency and reproducibility of tooth movement is improved, a significant reduction in the coefficients of friction was sought. Viscometric measurements were used to show that the characteristics of saliva remained unchanged throughout the investigation. Scanning electron micrographs and laser specular reflection were studied to illustrate the general appearance and quantitative magnitude of roughnesses. Frictional measurements of couples in the dry, the wet, and again in the dry state were evaluated at five different normal loads. The outcomes of the virgin materials show that arch wire alloy, rather than bracket product type or surface roughness, influence the frictional characteristics the most and that titanium wires generally cause higher frictional resistances than either stainless steel or cobalt-chromium wires. Friction tests of specimens that were run multiple times suggest that couples comprised of nickel titanium arch wires against ceramic brackets may actually improve as a result of a break-in period.     

不同材料在不同应力状态下的磁记忆信号特征

磁记忆是力磁效应的一种表现,目前关于力磁效应的基本规律及机理研究还没有统一的定论。为了进一步对磁记忆效应的机理及不同材料不同应力状态下磁记忆信号特征进行试验性的研究,对不同铁磁材料(Q235,20号钢,45号钢)圆棒试件进行静载拉伸试验,分别测量某固定点处在线加载和在线卸载2种不同应力状态下的磁记忆信号。试验结果表明:3种不同材料在线加载时磁记忆信号各表现出了不同的力磁效应;在线卸载时测得的磁记忆信号更能有利地分析构件的应力阶段;弹性阶段时磁荷梯度GF变化幅度不大,接近屈服阶段时,磁荷梯度变化幅度变大,可以利用磁荷梯度对低碳钢材料应力定量评价。试验结果为磁记忆效应机理研究提供了一定的依据,也为金属磁记忆检测的定量检测提供了潜在可能性。     

不同块石配比充填体的强度特性研究

利用RMT-150C型液压伺服控制系统进行不同块石含量胶结充填体的室内单轴抗压试验,得到块石质量百分数为0时抗压强度值为3.800 MPa,30%时抗压强度值为4.090 MPa,40%时抗压强度值为2.729 MPa,50%时抗压强度值为3.333 MPa,抗压强度值随块石含量增加呈现先增后减再增的变化规律;分析4组应力-应变曲线峰值应力对应的应变可得,块石含量为0时峰值应力对应的应变在0.006附近,30%时峰值应力对应的应变在0.0075附近,40%时峰值应力对应的应变在0.010附近,50%时峰值应力对应的应变在0.0125附近.说明块石的增加有效提高了充填体的变形能力,但在一定程度上削减了充填体的支承能力.     

Repair of Cerec porcelain with seven different systems

Intra-oral repair of fractured porcelain is a challenging clinical necessity, because time, economics, as well as possible trauma to teeth, often contra-indicate replacement of the original restoration. The purpose of this study was to evaluate the bond strength of seven different porcelain repair systems used in combination with Cerec Vitablocs Mark II porcelain. The systems were Scotchbond Multi-Purpose (SMP), All-Bond 2 (AB), Optibond (OB), C&B Metabond (CB), Imperva Bond (IB), Silistor (S) and Mirage Bond (MB). When Mirage Bond was used, the porcelain was either etched with 9.6 percent hydrofluoric acid for 2 min (10 specimens = MB1) or with 4 percent APF gel for 2 min (10 specimens = MB2). The shear bond strengths (SBS) of all the products were determined using an Instron. The effects of the pretreatments on the porcelain with different systems were also examined in a SEM. Data were statistically analysed (Wilcoxon Sum of Rank Test). The mean SBS (MPa) of the products were: SMP = 22.6 +/- 6.5; AB = 17.1 +/- 4.1; OB = 17.1 +/- 2.3; CB = 25.8 +/- 4.2; IB = 18.3 +/- 5.2; S = 16.4 +/- 3.7; MB1 = 13.1 +/- 3.9 and MB2 = 6 +/- 2.1. CB and SMP were significantly stronger (p < 0.05) than all other products, with MB2 statistically weaker (p < 0.01) than the other groups. Most specimens showed cohesive fractures in the porcelain, except when MB was used with 4 percent APF gel, where all samples fractured at the adhesive interface. It can be concluded that all seven systems can be used to repair Cerec Porcelain, except possibly MB when used in conjunction with 4 percent APF etchant.     

金纳米粒子的不同制备方法体系研究

分别采用葡萄糖-柠檬酸钠溶液体系的热化学法和柠檬酸钠溶液体系的光化学法制备了Au纳米粒子,并对所制备的Au纳米粒子进行了UV-Vis吸收光谱和TEM表征。其结果表明,两种不同体系所制备的金纳米粒子粒径均较小,尺寸均匀,并呈球形,单分散分布,具有一定的应用价值。     

Production and some structural characteristics of ultrafine systems

Conclusions All the methods examined enable ultrafine materials to be produced, generally characterized by a crystallite size of 100–200 Å. X-ray diffraction spectra indicate that such systems have atomic crystal structures with short-range order and a limited long-range order extending over distances commensurable with the size of coherent-scattering regions.Translated from Poroshkovaya Metallurgiya, No. 9 (225), pp. 10–14, September, 1981.     

不同生物质还原氧化铁的特性

以木屑、玉米秸秆、咖啡废渣和水解木质素4种生物质为还原剂,采用TG-FTIR联用、XRD、SEM等方法分析了各物质的化学成分及官能团构成,研究了不同生物质中碳和氢对氧化铁的还原反应特性。研究表明,生物质还原氧化铁的作用由气体和固定碳决定,其中气基还原的特征温度为806~822 K,碳还原的特征温度为1 116~1 132 K。4种生物质中,碳还原氧化铁的能力由强到弱依次是木屑>水解木质素>咖啡废渣>玉米秸秆,氢还原能力大小则为玉米秸秆>咖啡废渣>木屑>水解木质素。     

Static and dynamic characteristics of fluid-filled esophageal manometry systems

Esophageal manometric systems with water-filled catheters have been characterized by the use of model experiments. The examined parameters have been: catheter dimension, catheter compliance, catheter resistance, pump type, pump compliance, and perfusion flow. Accurate static pressure measurements have been obtained for perfused systems independently of the investigated parameters. The dynamic characteristics vary with catheter diameter and perfusion flow. For catheters with low diameter, a narrow bandwidth is obtained for the investigated perfusion flows. The results have been expressed in terms of an electric model of the measurement system. Perfusion pumps with low compliance are recommended to improve the dynamic properties of the measurement system.     

Economic management estimate of different environmentally-friendly animal husbandry systems

This contribution compares conventional and ecological animal production systems. This financial analysis considers dairy farming and pig production and takes into account the individual options and aims of the farms. The profitability changing a conventional animal production system to an ecological system depends on many different parameters. A general statement with regard to all farms and farm systems is not possible. In addition to the farmers qualification, the marketing options, the location of the farm, the mode of operation and the financial situation when change to ecological production is envisaged determine prospects for success and profitability.