A clinical trial of light cure acrylic resin for orthodontic use.
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OBJECTIVE: To ascertain whether or not the less porous surface associated with visible light cure appliances and the absence of free monomer had any measurable affect upon mucosal erythema, and to assess the durability of such appliances in a clinical context. DESIGN: A prospective randomized trial of visible light cure (Triad VLC) and autopolymerizing (Orthoresin) acrylic resin used as orthodontic base plate materials. SETTING: University Dental Hospital and School. SUBJECTS: Fifty subjects from a consecutively enrolled sample of 69 (19 drop outs) for removable appliance therapy (23 VLC, 27 AP). OUTCOME MEASURES: Erythema meter scores and appliance breakages. RESULTS: No statistical difference in mucosal erythema between the two materials was found. Fifty-two per cent of VLC appliances broke during a 6-month period, as opposed to 7 per cent of AP appliances. CONCLUSIONS: VLC appears to have no clinically beneficial effect on the oral mucosa compared with AP. VLC appliances are currently not sufficiently durable to make them a viable alternative to AP appliances. (+info)
Behavior of fibroblasts on a porous hyaluronic acid incorporated collagen matrix.
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A hyaluronic acid (HA) incorporated porous collagen matrix was fabricated at -70 degrees C by lyophilization. The HA incorporated collagen matrix showed increased pore size in comparison with collagen matrix. Biodegradability and mechanical properties of matrices were controllable by varying the ultraviolet (UV) irradiation time for cross-linking collagen molecules. Addition of HA to collagen matrix did not effect ultimate tensile stress after UV irradiation. HA incorporated collagen matrices demonstrated a higher resistance against the collagenase degradation than collagen matrix. In an in vitro investigation of cellular behavior using dermal fibroblasts on the porous matrix, HA incorporated collagen matrix induced increased dermal fibroblast migration and proliferation in comparison with collagen matrix. These results suggest that the HA incorporated collagen porous matrix assumes to enhance dermal fibroblast adaptation and regenerative potential. (+info)
Modelling the hydrodynamic resistance of bordered pits.
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Previous studies of the hydrodynamics of plant stems have shown that resistance to flow through bordered pits on the side walls of tracheids makes up a significant proportion of their total resistance, and that this proportion increases with tracheid diameter. This suggests a possible reason why tracheids with a diameter above around 100 microm have failed to evolve. This possibility has been investigated by obtaining an estimate for the resistance of a single pit, and incorporating it into analytical models of tracheid resistance and wood resistivity. The hydrodynamic resistance of the bordered pits of Tsuga canadensis was investigated using large-scale physical models. The importance of individual components of the pit were investigated by comparing the resistance of models with different pore sizes in their pit membrane, and with or without the torus and border. The estimate for the resistance of a real bordered pit was 1.70x10(15) Pa s m(-3). Resistance of pits varied with morphology as might be predicted; the resistance was inversely proportional to the pore size to the power of 0.715; removing the torus reduced resistance by 28%, while removal of the torus and border together reduced it by 72%. It was estimated that in a 'typical tracheid' pit resistance should account for 29% of the total. Incorporating the results into the model for the resistivity of wood showed that resistivity should fall as tracheid diameter increases. However, to minimize resistance wider tracheids would also need to be proportionally much longer. It is suggested that the diameter of tracheids in conifers is limited by upper limits to cell length or cell volume. This limitation is avoided by angiosperms because they can digest away the ends of their cells to produce long, wide vessels composed of many short cells. (+info)
Release from or through a wax matrix system. III. Basic properties of release through the wax matrix layer.
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Release property of reservoir device matrix tablet was examined. Wax matrix layer was prepared from physical mixture of lactose and hydrogenated castor oil to obtain basic release properties. Release process showed zero order kinetics in a steady state after a given lag times, and could be divided into two stages. The first stage was the formation process of water channel by dissolving the soluble component in the wax matrix layer. The lag time was considered to be the time required forming water channel and the time begun to release drug through the wax matrix layer at the same time. The lag time obtained by applying the square root law equation was well connected with the amount of matrix layer and mixed weight fraction of component in matrix layer. The second stage was the zero order release process of drug in the reservoir through the wax matrix layer. The release rate constants were calculated by taking into accounts of the thickness of matrix layer and permeability coefficient, and were well connected with the amount of matrix layer and mixed weight fraction of component. Also it was suggested that the tortuosity of matrix layer could be expressed by a function of the porosity defined by the mixed weight fraction. (+info)
Structure and development of stomata on the primary root of Ceratonia siliqua L.
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Stomata of various sizes are produced on the primary root of Ceratonia siliqua L. Most are generated during embryogenesis, prior to seed desiccation. They can be detected on the dry embryo in a wide zone just above the root tip. Initially, large stomata are formed. These have the ability to induce divisions of their neighbouring cells, creating particular cell patterns around them. Later, small perigenous stomata are generated. As the root grows following seed germination, the stomatal zone overlaps with that of the root hairs. Although root stomata of C. siliqua undergo a structural differentiation that seems almost identical to that of the elliptical stomata formed on leaves, they are unable to move and remain permanently open. Polarizing microscopy of fully differentiated stomata and young stomata at the stage of stomatal pore formation revealed deposition of radial cellulose microfibril systems on their periclinal walls. However, these systems were less developed than those on leaf stomata, a feature that might be responsible for their inactivity. Besides, plastids of the root guard cells (GCs) do not differentiate into chloroplasts but function solely as amyloplasts. Root stomata have a short life span. During rapid and intense root growth, GCs cannot keep pace with the elongation of their neighbouring rhizodermal cells. They therefore split in their mid-region, transversely to the stoma axis. The two parts of the transversely torn stoma are dragged apart and a large opening is formed on the root surface, just above the substomatal cavity. The root stomata, together with these openings, may facilitate increased gaseous exchange during respiration and/or an increased transfer of some nutrients and water in the rapidly growing primary root. (+info)
The pore density in the inner wall endothelium of Schlemm's canal of glaucomatous eyes.
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PURPOSE: In a prior study, it has been reported that glaucomatous eyes have a significantly lower density of pores in the inner wall of Schlemm's canal than do normal eyes. However, in that study the glaucomatous eyes were fixed at much lower flow rates than the normal eyes, and that is now known to affect inner wall pore density. The objective of the current study was to compare the inner wall's pore density in glaucomatous and normal eyes, accounting for the effects of fixation conditions. METHODS: Outflow facility was measured in enucleated glaucomatous human eyes. Eyes were fixed under constant flow conditions, microdissected to expose the inner wall of Schlemm's canal, and prepared for scanning electron microscopy (SEM). The density and diameter of the two subpopulations of pores in the inner wall, intracellular and intercellular (or "border") pores, were measured. Data were compared with those in previous studies of normal eyes. RESULTS: As previously reported, pore density decreased with increasing postmortem time and increased with increasing volume of fixative passed through the outflow pathway and with increasing fixation time. Linear regression analysis indicated that glaucomatous eyes had less than one fifth the number of pores than normal eyes have, after accounting for the influence of volume of fixative perfused through the eyes (835 pores/mm(2) in normal eyes versus 160 pores/mm(2) in glaucomatous eyes). A nonlinear regression of pore density versus fixative volume produced a pore density at zero fixative volume that was not statistically different from zero. If true, this implies that all (or nearly all) inner wall pores observed by SEM are fixation artifacts. The density of intracellular pores and the diameter of these pores correlated with the density and diameter of the border pores, respectively. CONCLUSIONS: Inner wall pores are reduced in glaucomatous eyes. If pores are physiological structures, the elevated intraocular pressure characteristic of glaucoma may be explained by decreased porosity of the inner wall endothelium. Both border and intracellular pores seem to be induced in a similar fashion by fixation. The unlikely possibility that all inner wall pores are fixation-induced cannot be excluded. If so, a fundamental reassessment of the mechanism by which aqueous humor crosses the inner wall endothelium is necessary. (+info)
Rate of increase of osmolality determines osmotic tolerance of mouse inner medullary epithelial cells.
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Renal inner medullary cells survive and function despite interstitial osmolality of 600-1,700 mosmol/kgH(2)O or more. In contrast, much smaller changes kill cells in tissue culture. Using mouse inner medullary epithelial cells at passage 2, we defined factors that might account for the difference. Most of the factors that we tested, including addition of hormones (insulin-like growth factor I, epidermal growth factor, or deamino-8-D-arginine vasopressin), growth on porous supports, and presence of matrix proteins (collagen I, collagen IV, fibronectin, laminin, or fibrillar collagen I), have no significant effect. However, the time course of the change makes a major difference. When osmolality is increased from 640 to 1,640 mosmol/kgH(2)O by addition of NaCl and urea in a single step, only 30% of cells survive for 24 h. However, when the same increase is made linearly over 20 h, 89% of the cells remain viable 24 h later. We conclude that gradual changes in osmolality, e.g., in vivo, allow cells to survive much greater changes than do the step changes routinely used in cell culture experiments. (+info)
Use of infrared thermography for monitoring stomatal closure in the field: application to grapevine.
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This paper reviews and discusses strategies for the use of thermal imaging for studies of stomatal conductance in the field and compares techniques for image collection and analysis. Measurements were taken under a range of environmental conditions and on sunlit and shaded canopies to illustrate the variability of temperatures and derived stress indices. A simple procedure is presented for correcting for calibration drift within the images from the low-cost thermal imager used (SnapShot 225, Infrared Solutions, Inc.). The use of wet and dry reference surfaces as thresholds to eliminate the inclusion of non-leaf material in the analysis of canopy temperature is discussed. An index that is proportional to stomatal conductance was compared with stomatal measurements with a porometer. The advantages and disadvantages of a possible new approach to the use of thermal imagery for the detection of stomatal closure in grapevine canopies, based on an analysis of the temperature of shaded leaves, rather than sunlit leaves, are discussed. Evidence is presented that the temperature of reference surfaces exposed within the canopy can be affected by the canopy water status. (+info)