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OBJECTIVE: To evaluate the effects of 5 kinds of base materials on the stress distribution and deflection in amalgam- restored teeth. METHODS: A computerized two-dimensional finite-element of the tooth model first molar was established. Various dental cements with a thickness of 0.5 mm and amalgam restorations with thickness of 2 mm in the prepared cavity were simulated and subjected to microhardness test (load=45 kg). The stresses and deflections along the cavity wall interface were analyzed by finite-element method. RESULTS: High stress and deflection occurred mainly at the line angle of the cavity, this could be magnified by using cements with lower elasticity modulus. The maximum compressive stress at the line angle induced by common ZOE or Ca(HO)(2) was increased 3.3 times or 2 times and deflections increased by 40% and 25% respectively that by Zinc phosphate and glass ionomer. CONCLUSION: Modulus elasticity of cement plays an important role in affecting the fracture strength of the amalgam restored tooth. The lower the elasticity modulus, the higher the stresses and deflections induced in the dentine. From the point of mechanical property, zinc phosphate is one of the best dental cements.
Hydromedusan jellyfish swim by rhythmic pulsation of their mesogleal bells. A single swimming muscle contracts to create thrust by ejecting water from the subumbrellar cavity. At the end of the contraction, energy stored in the deformation of the mesogleal bell powers the refilling stage, during which water is sucked back into the subumbrellar cavity. The mesoglea is a mucopolysaccharide gel reinforced with radially oriented fibres made primarily of a protein homologous to mammalian fibrillin. Most of the energy required to power the refill stroke is thought to be stored by stretching these fibres. The elastic modulus of similar fibrillin-rich fibres has been measured in other systems and found to be in the range of 0.2 to 1.1 MPa. In this paper, we measured the diameters of the fibres, their density throughout the bell, and the mechanical behaviour of the mesoglea, both in isolated samples and in an intact bell preparation. Using this information, we calculated the stiffness of the fibres of the hydromedusa Polyorchis penicillatus, which we found to be approximately 0.9 MPa, similar in magnitude to other species. This value is two orders of magnitude more compliant than the stiffness of the component fibrillin microfibrils previously reported. We show that the structure of the radial fibres can be modelled as a parallel fibre-reinforced composite and reconcile the stiffness difference by reinterpreting the previously reported data. We separate the contributions to the bell elasticity of the fibres and mesogleal matrix and calculate the energy storage capacity of the fibres using the calculated value of their stiffness and measured densities and diameters. We conclude that there is enough energy potential in the fibres alone to account for the energy required to refill the subumbrellar cavity.
The elasticity modulus E parallel in the membrane plane is frequency-independent in the range of 5--10 c.p.s. At room temperature E parallel 6-10(8) dn/cm2, at 4 degrees C E parallel depends strongly upon the degree of deformation-relative membrane surface change delta S/S, E parallel falls from 2-10(9) dn/cm2 if delta S/S = 0.1% down to 6-10(8) dn/cm2 if delta S/S = 1%. This property of E parallel explains the ability of mechanoreceptor membranes to produce a reaction if small stimulii are applied and to oppose the destruction if the latter are large.
Electrical and optical changes were measured in bovine sternomandibularis and porcine sternocephalicus strips tested sinusoidally in a rigorometer up to 3 h postmortem. Rigor development was detected by decreased muscle elongation, decreased stress-strain hysteresis area, and increased elastic modulus. Elastic modulus was affected by loading rate (r = .98, P < .005) from loading rates of 3.6 to 13.3 kPa/s. Capacitance decreased and resistance increased at 120 Hz, 1 kHz, and 10 kHz as rigor developed. Sometimes changes were irregular at one frequency but steady at another. The most consistent electrical predictors of rigor development were capacitance at 120 Hz and resistance at 10 kHz. Electrical impedance changed as muscle strips were stretched in the rigorometer, so that dimensional effects could be a source of error if testing causes muscle contraction. The dominant fiber-optic reflectance changes during rigor development were increases toward 400 nm and decreases toward 700 nm, although transient increases were sometimes detected toward 700 nm. Optical changes generally were later than electrical changes. All these complex changes are an obstacle to the early prediction of pH-dependent aspects of meat quality from electrical and optical measurements.
Several recent studies have shown that cells respond to the elastic modulus and elasticity gradients on soft substrates. However, traditional macroscale methods for measuring elastic modulus cannot resolve elastic gradients or differences between the macroscale and microscale elastic modulus of layered tissues. Here, we present a technique for measurement of the microscale elastic modulus of soft, hydrated gels and tissues. This technique requires less equipment than equivalent atomic force microscopy (AFM) and can easily measure larger samples with high adhesiveness. We validate this technique by measuring the microscale modulus of a hydrogel with elasticity that does not depend on measurement scale. We show that the elastic modulus measured using microindentation correlates with measurements using AFM and the macroscale tensile modulus. We verified the ability of this technique to characterize a hydrogel with an elastic gradient of 2.2 kPa/mm across 19 mm and to measure the microscale elastic modulus of the endothelial side of human greater saphenous vein, which is an order of magnitude less than the whole vein macroscale modulus. This simple, inexpensive system allows the measurement of the spatial organization of microscale elastic properties of fully hydrated, soft gels and tissues as a routine laboratory technique.
A comparative investigation of multicomponent thin films based on the systems Ti-Ca-C-O-(N), Ti-Zr-C-O-(N), Ti-Si-Zr-O-(N) and Ti-Nb-C-(N) is presented. TiC(0.5) + 10%CaO, TiC0.5 + 20%CaO, TiC0.5 + 10%ZrO2, TiC0.5 + 20%ZrO2, Ti5Si3 + 10%ZrO2, TiC0.5 + 10%Nb2C and TiC0.5 + 30%Nb2C composite targets were manufactured by means of self-propagating high-temperature synthesis, followed by DC magnetron sputtering in an atmosphere of argon or in a gaseous mixture of argon and nitrogen. The films were characterized in terms of their structure, chemical composition, surface topography, hardness, elastic modulus, elastic recovery, surface charge, friction coefficient, and wear rate. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments. In vitro studies involved the investigation of the proliferation of Rat-1 fibroblasts and IAR-2 epithelial cells on the tested films, morphometric analysis and actin cytoskeleton staining of the cells cultivated on the films. In vivo studies were fulfilled by subcutaneous implantation of Teflon plates coated with the tested films in mice and analysis of the population of cells on the surfaces. The films deposited under optimal conditions showed high hardness in the range of 30-37 GPa, significant reduced Young's modulus, low friction coefficient down to 0.1-0.2 and low wear rate in comparison with conventional magnetron-sputtered TiC and TiN films. The surface of all films was negatively charged with an outstanding shift between the Ar and Ar + N2 Zeta potential curves that reaches 5 mV at the highest pH values. We did not detect statistically significant differences in the attachment, spreading and cell shape of cultured IAR-2 and Rat-1 cells on the Ti-Ca-C-O-(N), Ti-Zr-C-O-(N) (TiC0.5 + 10%ZrO2 target), Ti-Si-Zr-O-(N) films and the uncoated substrata. The adhesion and proliferation of cultured cells in vitro was perfect at all investigated films. Assessment of the population of cells covering on the Teflon plates coated with the Ti-Ca-C-O-(N) and Ti-Zr-C-O-(N) films after 16 weeks of subcutaneous implantation revealed the high biocompatibility level of tested films and absence of inflammatory reactions in mice. Contrary, the epitheliocytes and fibroblasts cultivated on the Ti-Zr-C-O-(N) (TiC0.5 + 20%ZrO2 target) and Ti-Nb-C-(N) films had disturbing actin cytoskeleton.
Cholinergic synaptic vesicles from Torpedo californica have been probed with the atomic force microscope in aqueous buffers to map and measure their elastic properties. Elastic properties were mapped with a new atomic force microscope technique known as force mapping. Force mapping of vesicles showed that the centers of the vesicles are harder or stiffer than the peripheral areas in the three buffers that were investigated. These were an isoosmotic buffer, a hypoosmotic buffer, and an isoosmotic buffer with 5 mM CaCl2 added. The hardness of the vesicular centers was quantified by calculation of the elastic modulus. Elastic moduli were in the range of 2-13 x 10(5) Pa. Vesicular centers were hardest in calcium-containing buffer and softest in isoosmotic buffer. Hypotheses are presented for the composition and function of the hard centers.
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RBC membrane shear elastic modulus and membrane viscosity are two important indexes reflecting RBC membrane viscoelasticity. Their variation was investigated in this study after rabbits were radiated with 60Co. With a new ektacytometer, we measured the small deformation index (DId) and the half-time of deformation relaxation (t0.5) of RBC in flow field then we calculated RBC membrane shear elastic modulus and membrane viscosity. We found that the value of RBC membrane shear elastic modulus and membrane viscosity continuously increased from 0 to 16th day then continuously decreased and tended to be stable on 60th day or so. The reason may lie in the variation of proportion of new and old RBC in blood and variation of microconformation of RBC membrane after rabbits were radiated with 60Co.
Values of modulus of elasticity of cell walls and strength level of cells Escherichia coli cultivated in the carbon, nitrogen and phosphorus deficient media or incubated in the magnesium-free medium were determined. Elastic modulus of cells grown in the magnesium-free medium was by two order of magnitude lower than that of the control cells. Elastic modulus of cells cultivated in the nitrogen and carbon deficient media was by one and two orders of magnitude lower than in the control cells whereas strength level was by 1.15 and 1.39 times higher, respectively. Elastic modulus of cells grown in the phosphorus deficient medium remained undetermined and strength level of those cells proved to be the lowest (0.9 of the control).
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The present study measured the diametral compressive strength, flexural strength, and modulus of elasticity of composite resins used in inlay/onlay systems. The effect of additional curing also was determined. SR-Isosit material had the highest diametral compressive strength, and SR-Isosit-Dentin material had the lowest flexural strength. The SR-Isosit composite resins had lowest elastic modulus and Estilux posterior C VS resin the highest. A negative correlation was found between diametral compressive strength and elastic modulus of the materials. It was concluded that the additional curing of Brilliant resin did not result in improved mechanical properties. For Estilux resin, additional curing increased flexural strength and modulus of elasticity.
Custom impression trays are necessary for accurate impressions in fixed prosthodontics when using polysulfide impression materials. These custom impression trays are needed to provide for a uniform thickness of impression material to minimize distortion. Custom impression trays have historically been made from acrylic resin. New materials have been developed as alternatives to acrylic resin, and this study evaluates one product currently available that is composed of polycaprolaitone. This study evaluates the modulus of elasticity of polycaprolaitone as compared with acrylic resin, and also evaluates the amount of permanent deformation of the new material when placed under a load. The elastic modulus of polycaprolaitone was tested using three-point bending of specimens placed in a universal mechanical test system. The elastic modulus of the new material was found to be significantly lower than that of acrylic resin. The next test evaluated the amount of permanent deformation of the polycaprolatione material when specimens approximating the shape and size of custom impression trays were placed under a load. These trays were placed in a universal mechanical test system and differing loads were placed on them. Results showed that although the trays deformed at relatively low loads, all deformation was fully recovered within a clinically insignificant period of time (less than 30 seconds). From these experiments it was concluded that although the polycaprolaitone material has a lower modulus of elasticity and will deform under relatively low loads, the material recovers completely, and thus the deformation would not interfere with the clinical performance of polycaprolaitone as a custom tray material.
BACKGROUND: We re-examine the adequacy of an albino (hairless) mouse dorsal distally based skin flap model by determining elastic modulus and by assessing viability after application of rapid intermittent stretch to facilitate wound closure. MATERIAL/METHODS: Modulus of elasticity was determined with materials testing. Viability was accessed by laser Doppler flowmetry and by quantifying marginal tissue necrosis (mm2) at 5 days. Effective length gained and tension relieved were measured by subjecting flaps to simple undermining plus 3-10 g of initial tension (linear stretch) using a skin hook. Immediate hemispherical stretch was applied with an implanted subcutaneous silicone balloon (Rapid Intraoperative Tissue Expansion or RITE) at 1 or 2 cycles of 3-8 min and 6-12 ml for each cycle. Flaps subjected to simple and extensive undermining with or without application of initial linear stretch served as postoperative controls. RESULTS: The elastic modulus of 9.85 (1.02) N/mm2 approximated the skin of the human face. Flowmetry demonstrated that all flaps were adequately perfused. Stretching significantly decreased flap tension and increased flap length over simple undermining alone. It drastically improved flap viability by provoking a 50-75% decline in 5-day necrosis. The benefits were dependent upon the initial linear tension applied, but independent of the timing, cycling, and volume selected for RITE and the flap dimensions at closure. CONCLUSIONS: Results demonstrate that the albino (hairless) mouse dorsal distally based skin flap is a reliable model for studying wound closure and that rapid intermittent stretching in this model facilitates closure and wound healing.
Because of the existence of large reserves, the production of heavy oils is presently the object of much interest. Some heavy oil reservoirs show anomalous behavior in primary production, with rates of production better than predicted. In Canada and Venezuela some heavy oils are produced in the form of "bubbly" oil, which is stable for several hours in open vessels. These crude oils are therefore commonly called "foamy oils". Since the presence of bubbles could be responsible for an enhanced rate of production, a better knowledge of the properties of the gas-oil interface is desirable. We have experimentally studied the effect of concentration of asphaltenes and resins on static and dynamic properties of oil-air interfaces and also on bulk viscosity. The experiments include surface tension measurements using the pendant-drop method, surface viscosity by the oscillating-drop method, foamability by continuous gas injection, and film lifetime. All the experiments were performed using resins and asphaltenes in toluene solutions at 20 degrees C. At first asphaltenes enhance foamability and film lifetime. All the experiments performed showed a change in regime for asphaltene concentrations around 10% by weight, possibly due to clustering. At the studied concentrations, the adsorption process at the air-oil interface is not diffusion controlled but rather involves a reorganization of asphaltene molecules in a network structure. The formation of a solid skin is well identified by the increase of the elastic modulus. This elastic modulus is also an important property for foam stability, since a rigid interface limits bubble rupture. The interface rigidity at long times decreases with increases in resin fraction, which could decrease foam stability as well as emulsion stability. Copyright 2001 Academic Press.
OBJECTIVES: This investigation is to understand the role of free water in the dentinal tubules on the mechanical integrity of bulk dentine. METHODS: Three different experiments were conducted in this study. In experiment 1, three-dimensional models of dentine with gradient elastic modulus, homogenous elastic modulus, and with and without hydrostatic pressure were simulated using the finite element method. Static compressive loads of 15, 50 and 100 N were applied and the distribution of the principal stresses, von Mises stresses, and strains in loading direction were determined. In experiment 2, experimental compression testing of fully hydrated and partially dehydrated dentine (21 degrees C for 72 h) was conducted using a Universal testing machine. In experiment 3, Fourier transform infrared spectroscopic analysis of hydrated and partially dehydrated dentine was carried out. RESULTS: The finite element analysis revealed that the dentine model with simulated hydrostatic pressure displayed residual tensile stresses and strains in the inner region adjacent to the root canal. When external compressive loads were applied to the model, the residual stresses and strains counteracted the applied loads. Similarly the hydrated specimens subjected to experimental compression loads showed greater toughness when compared to the partially dehydrated specimens. The stress at fracture was significantly higher in partially dehydrated specimens (p=0.014), while the strain at fracture was significantly higher in hydrated dentine specimens (p=0.037). SIGNIFICANCE: These experiments highlighted the distinct role of free water in the dentinal tubules and hydrostatic pressure on the stress-strain distribution within the bulk dentine.