The influence of simulated masticatory loading regimes on the bi-axial flexure strength and reliability of a Y-TZP dental ceramic

OBJECTIVES: The purpose of the current study was to examine the influence of simulated masticatory loading regimes, to which all-ceramic crown or bridge restorations will routinely be subjected during their service-life, on the performance of a yttria-stabilised tetragonal zirconia polycrystalline (Y-TZP) dental ceramic. METHODS: Ten sets of 30 Y-TZP ceramic discs (13 mm diameter, 1.48-1.54 mm thickness) supplied by the manufacturer were randomly selected. Six groups were loaded for 2000 cycles at 500 N (383-420 MPa), 700N (536-588 MPa) and 800 N (613-672 MPa) with three groups maintained dry and the remaining three groups loaded while immersed in water at 37+/-1 degrees C. A further two groups underwent extended simulated masticatory loading regimes at 80 N (61-67 MPa) for 10(4) and 10(5)cycles under dry conditions. The mean bi-axial flexure strengths, standard deviations and associated Weibull moduli (m) were determined. The surface hardness was also determined using the Vickers hardness indentation technique. RESULTS: No significant difference (P>0.05) was identified in the bi-axial flexure strength of the simulated masticatory loading regimes and the control specimens loaded dry or wet. A significant increase in m was identified for the Y-TZP specimens following loading while immersed in water (8.6+/-1.6, 8.5+/-1.6 and 10.3+/-1.9) compared with the control (7.1+/-1.3). However, the extended loading regime to 10(5)cycles resulted in a significant reduction in the m of the Y-TZP specimens (5.3+/-1.0) compared with the control. Localised areas of increased surface hardness were identified to occur directly beneath the spherical indenter. CONCLUSIONS: The occurrence of localised areas of increased surface hardness could be the result of either a transformation toughening mechanism or crushing and densification of the material beneath the indentor manifested as the formation of a surface layer of compressive stresses that counteracted the tensile field generated at the tip of a propagating crack which increased the Weibull modulus of the Y-TZP specimens. The reduced reliability of the Y-TZP specimens loaded to 80 N for 10(5)cycles was associated with the accumulation of subcritical damage as a result of the extended nature of loading.     

Influence of Type and Level of Water-Soluble Additives on Drug Release and Surface and Mechanical Properties of Surelease® Films

Ethylcellulose in combination with water-soluble additives has been used in the development of microporous membrane-coated dosage forms. In the present study, application of three types of water-soluble additives, namely polyethylene glycols (PEG 400, 3350, and 8000), maltodextrins (Maltrin M150, M100, and M040 in the order of lower to higher average polymer size and molecular weight; dextrose equivalence 16.9, 11.1, and 4.8, respectively), and xylitol, as porosity modifiers in the films of a commercially available aqueous ethylcellulose dispersion (Surelease/E-7-7060 plasticized with glyceryl tricaprylate/caprate) was investigated. The effect of type and level of these additives on drug release characteristics and surface and mechanical properties of the polymeric films was studied. Each additive was incorporated at 20 and 30% levels in the polymeric dispersion based on its solids content. Ibuprofen tablets were coated using the polymeric dispersion with and without additive at 3% w/w coat level in a fluid-bed equipment. The coated tablets were evaluated for their drug release rate, coat reflectivity (gloss), Brinell hardness, and elastic modulus. Differential scanning calorimetric analysis of the films was performed to determine the physico-chemical changes in the applied film-coats. The rate of drug release, hence film porosity, was observed to be dependent on the type and level of the additive added. The molecular weight of the additive and its concentration in the polymeric dispersion had significant influence on the rate of drug release, hardness, and elasticity of the film-coats.     

Influence of hardness on the bioavailability of silver to a freshwater snail after waterborne exposure to silver nitrate and silver nanoparticles

Abstract

The release of Ag nanoparticles (AgNPs) into the aquatic environment is likely, but the influence of water chemistry on their impacts and fate remains unclear. Here, we characterize the bioavailability of Ag from AgNO₃ and from AgNPs capped with polyvinylpyrrolidone (PVP AgNP) and thiolated polyethylene glycol (PEG AgNP) in the freshwater snail, Lymnaea stagnalis, after short waterborne exposures. Results showed that water hardness, AgNP capping agents, and metal speciation affected the uptake rate of Ag from AgNPs. Comparison of the results from organisms of similar weight showed that water hardness affected the uptake of Ag from AgNPs, but not that from AgNO₃. Transformation (dissolution and aggregation) of the AgNPs was also influenced by water hardness and the capping agent. Bioavailability of Ag from AgNPs was, in turn, correlated to these physical changes. Water hardness increased the aggregation of AgNPs, especially for PEG AgNPs, reducing the bioavailability of Ag from PEG AgNPs to a greater degree than from PVP AgNPs. Higher dissolved Ag concentrations were measured for the PVP AgNPs (15%) compared to PEG AgNPs (3%) in moderately hard water, enhancing Ag bioavailability of the former. Multiple drivers of bioavailability yielded differences in Ag influx between very hard and deionized water where the uptake rate constants (k_uw, l?g^?1?d^?1?±?SE) varied from 3.1?±?0.7 to 0.2?±?0.01 for PEG AgNPs and from 2.3?±?0.02 to 1.3?±?0.01 for PVP AgNPs. Modeling bioavailability of Ag from NPs revealed that Ag influx into L. stagnalis comprised uptake from the NPs themselves and from newly dissolved Ag.     

船舶反渗透海水淡化水的水质检测及卫生学分析

目的:分析船舶反渗透海水淡化水的水质,从卫生学探讨船舶反渗透淡化水作为饮用水长期饮用对船员健康的可能影响。方法:水质分析按照《生活饮用水标准检验方法》(GB/T5750-2006)进行,并比较船舶反渗透海水淡化水、港口直供水、舱贮饮用水的水质差异。结果:船舶反渗透海水淡化水中氟化物<0.01 mg/L,总硬度<1 mg/L,显著低于港口直供水和舱贮饮用水;同时硼为1.03 mg/L,超过《生活饮用水卫生标准》(GB5749-2006)限值的两倍。结论:从卫生学分析,长期饮用船舶反渗透海水淡化水对船员的健康可能有影响,建议适度增加船舶反渗透海水淡化水中氟、钙、镁等营养元素水平,同时进一步脱除硼,从而更好地保护船员的身心健康。     

北京市某区浅层自备井水总硬度的影响因素分析

目的 了解北京某区浅层自备水井中总硬度含量的影响因素.方法 选取北京某区5眼浅层自备井和1眼深层自来水厂水源井.分别于2004-2010年枯水期(4、5月)和丰水期(8、9月),在井口泵房采集井水水样,检测总硬度、pH值、氯化物、硫酸盐.结果 共采集自备井水样70件,总硬度合格36件,合格率仅为51.43%.不同年度间...     

Effects of low power red laser on induced-dental caries in rats

OBJECTIVE: The purpose of this study was to investigate the effects of low power red laser associated with acidulated phosphate fluoride on the development of induced-dental caries in rats. DESIGN: Dental caries were induced in molars of 40 rats divided into five groups: control group (CG), the teeth were not submitted to any treatment; laser group (LG), teeth were irradiated with a low power red laser (LPRL), power of 30 mW and dose of 5 J/cm(2); fluoride group (FG), teeth were treated with topical acidulated phosphate fluoride (APF) 1.23% applied for 4 min; laser+fluoride group (LFG), teeth were irradiated with LPRL followed by APF; fluoride+laser group (FLG), teeth were treated with APF followed by LPRL. The animals were killed after 48 days, and the first and second molars were extracted to analyze the caries lesion area, microhardness, and calcium and phosphorus ratio. RESULTS: There were no statistical differences among FG, LFG, and FLG regarding to caries area and microhardness, although the caries area were smaller in LFG. Ca/P ratio did not show significant differences among all groups. CONCLUSIONS: Although LPRL before APF application appeared to diminish the caries progression, LPRL did not present any additional benefit compared with acidulated phosphate fluoride on the prevention of induced-dental caries in rats.     

Burger Model as the Best Option for Modeling of Viscoelastic Behavior of Resists for Nanoimprint Lithography

In this study, Atomic Force Microscopy-based nanoindentation (AFM-NI) with diamond-like carbon (DLC) coated tip was used to analyze the mechanical response of poly(methyl methacrylate) (PMMA) thin films (thicknesses: 235 and 513 nm) on a silicon substrate. Then, Oliver and Pharr (OP) model was used to calculate hardness and Young’s modulus, while three different Static Linear Solid models were used to fit the creep curve and measure creep compliance, Young’s modulus, and viscosity. Values were compared with each other, and the best-suited method was suggested. The impact of four temperatures below the glass transition temperature and varied indentation depth on the mechanical properties has been analyzed. The results show high sensitivity on experiment parameters and there is a clear difference between thin and thick film. According to the requirements in the nanoimprint lithography (NIL), the ratio of hardness at demolding temperature to viscosity at molding temperature was introduced as a simple parameter for prediction of resist suitability for NIL. Finally, thinner PMMA film was tentatively attributed as more suitable for NIL.     

Effect of Laser Processing Parameters on Microstructure,Hardness and Tribology of NiCrCoFeCBSi/WC Coatings

In the present study, pulsed laser post-processing was applied to improve the properties of the thermally sprayed NiCrCoFeCBSi/40 wt.% WC coatings. The powder mix was deposited onto a mild steel substrate by flame spray method and then the as-sprayed coatings were processed by Nd:YAG laser. The peak power density applied was between 4.00 × 10⁶ and 5.71 × 10⁶ W/cm², and the laser operating speed ranged between 100 and 400 mm/min, providing processing in a melting mode. Scanning electron microscopy, energy dispersive spectroscopy, Knop hardness measurements, and “ball-on-disc” dry friction tests were applied to study the effect of the processing parameters on the geometry of laser pass and microstructure, hardness, and tribology of the processed layers. The results obtained revealed that pulsed laser processing provides a monolithic remelted coating layer with the microstructure of ultrafine, W-rich dendrites in Ni-based matrix, where size and distribution of W-rich dendrites periodically vary across remelted layer depth. The composition of W-rich dendrites can be attributed to a carbide of type (W, Cr, Ni, Fe)C. The cracks sensitivity of coatings was visibly reduced with the reduction of power density applied. The hardness of coatings was between ~1070 and ~1140 HK0.2 and correlated with microstructure size, being dependent on the processing parameters. The friction coefficient and wear rate of coatings during dry sliding were reduced by up to ~30% and up to ~2.4 times, respectively, after laser processing.     

Effect of Steel-Cutting Technology on Fatigue Strength of Steel Structures: Tests and Analyses

This paper presents the results of comparative fatigue tests carried out on steel S355J2N specimens cut out using different cutting methods, i.e., plasma cutting, water jet cutting, and oxyacetylene cutting. All the specimens were subjected to cyclic loading from which appropriate S-N curves were obtained. Furthermore, face-of-cut hardness and roughness measurements were carried out to determine the effect of the cutting method on the fatigue strength of the tested steel. The fatigue strength results were compared with the standard S-N fatigue curves. The fatigue strength of the specimens cut out with oxyacetylene was found to be higher than that of the specimens cut out with plasma even though the surface roughness after cutting with plasma was smaller than in the case of the other cutting technology. This was due to the significant effect of material hardening in the heat-affected zones. The test results indicate that, in comparison with the effect of the cutting technology, the surface condition of the specimens has a relatively small effect on their fatigue strength.