Polymerization shrinkage: effects of boundary conditions and filling technique of resin composite restorations

Objective: To evaluate the linear polymerization shrinkage (LPS) and the effect of polymerization shrinkage of a resin composite and resin-dentin bond strength under different boundary conditions and filling techniques.Methods: Two cavities (4 x 4 x 2 MM) were prepared in bovine incisors (n = 30). The teeth were divided into three groups, according to boundary conditions: In group TE, the total-etch technique was used. In group EE, only enamel was conditioned, and in group NE, none of the watts of the cavities were conditioned. A two-step adhesive system was applied to all cavities. The resin composite was inserted in one (B) or three increments (1), and tight-cured with 600 mW/cm(2) (80 s). The LPS (%) was measured in the top-bottom direction, by placing a probe in contact with resin composite during curing. Enamel and total mean gap widths were measured (400 x) in three slices obtained after sectioning the restorations. Then, the slices were sectioned again, either to obtain sticks from the adhesive interface from the bottom of the cavity or to obtain resin composite sticks (0.8 mm(2)) to be tested for tensile strength (Kratos machine, 0.5 mm/min). The data was subjected to a two-way repeated measures ANOVA and Tukey's test for comparison of the means (alpha = 0.05).Results: the highest percentage of LPS was found for the TE when bulk fitted, and the lowest percentage of LPS was found in the Hand NE when incrementally fitted. The resin dentin bond strength was higher and the total mean gap width was tower for TE group; no significant effect was detected for the main factor fitting techniques. No difference was detected for the tensile strength of resin composite among the experimental groups.Conclusions: the filling technique is not able to minimize effects of the polymerization shrinkage, and bonding to the cavity watts is necessary to assure reduced mean gap width and high bond strength values. (C) 2004 Elsevier Ltd. All rights reserved.

Tibial segmental bone defect treated with bone plate and cage filled with either xenogeneic composite or autologous cortical bone graft

Tibia segmental defect healing in sheep were clinically, radiographically and histologically evaluated. Twelve young sheep aged four to five months were divided into two groups, G1 and G2. A 3.5 cm long segmental defect was created in the right tibial diaphysis with maintenance of the periosteum. The bone defects in both groups were stabilized with a bone plate combined with a titanium cage. In G1 the cage was filled with pieces of autologous cortical bone graft. In G2 it was filled with a composite biomaterial which consisted of inorganic bovine bone, demineralized bovine bone, a pool of bovine bone morphogenetic proteins bound to absorbable ultra-thin powdered hydroxyapatiteand bone-derived denaturized collagen. Except for one G1 animal, all of them showed normal limb function 60 days after surgery. Radiographic examination showed initial formation of periosteal callus in both groups at osteo-tomy sites, over the plate or cage 15 days postoperatively. At 60 and 90 days callus remodeling occurred. Histological and morphometric analysis at 90 days after surgery showed that the quantity of implanted materials in G1 and G2 were similar, and the quantity of new bone formation was less (p = 0.0048) and more immature in G1 than G2, occupying 51 +/- 3.46% and 62 +/- 6.26% of the cage space, respectively. These results suggest that the composite biomaterial tested was a good alternative to autologous cartical bone graft in this experimental ovine tibial defect. However, additional evaluation is warranted prior to its clinical usage.

Effect of calcium ions on rat osseous plate alkaline phosphatase activity

Rat osseous plate alkaline phosphatase is a metalloenzyme with two binding sites for Zn2+ (sites I and III) and one for Mg2+ (site II). This enzyme is stimulated synergistically by Zn2+ and Mg2+ (Ciancaglini et al., 1992) and also by Mn2+ (Leone et al., 1995) and Co2+ (Ciancaglini et al., 1995). This study was aimed to investigate the modulation of enzyme activity by Ca2+. In the absence of Zn2+ and Mg2+, Ca2+ had no effects on the activity of Chelex-treated, Polidocanol-solubilized enzyme. However, in the presence of 10 mu M MgCl2, increasing concentration of Ca2+ were inhibitory, suggesting the displacement of Mg2+ from the magnesium-reconstituted enzyme. For calcium-reconstituted enzyme, Zn2+ concentrations Zip to 0.1 mu M were stimulatory, increasing specific activity from 130 U/mg to about 240 U/mg with a K-0.5 = 8.5 nM. Above 0.1 mu M Zn2+ exerted a strong inhibitory effect and concentrations of Ca2+ up to I mM were not enough to counteract this inhibition, indicating that Ca2+ was easily displaced by Zn2+. At fixed concentrations of Ca2+, increasing concentrations of Mg2+ increased the enzyme specific activity from 472 U/mg to about 547 U/mg, but K-0.5 values were significantly affected (from 4.4 mu M to 38.0 mu M). The synergistic effects observed for the activity of Ca2+ plus magnesium-reconstituted enzyme, suggested that these two ions bind to the different sites. A model to explain the effect of Ca2+ on the activity of the enzyme is presented. (C) 1997 Elsevier B.V.

OSSEOUS PLATE ALKALINE-PHOSPHATASE IS ANCHORED BY GPI

Alkaline phosphatase activity was released up to 100% from the membrane by using 0.1 U of phosphatidylinositol-specific phospholipase C from B. thuringiensis. The Mr of solubilized enzyme was 145,000 by Sephacryl S-300 gel filtration and 66,000 by SDS-PAGE, suggesting a dimeric structure. Solubilization of the membrane-bound enzyme with phospholipase C did not destroy its ability to hydrolyze p-nitrophenyl phosphate (PNPP) (264.3 mu mol min(-1) mg(-1)), ATP (42.0 mu mol min(-1) mg(-1)) and pyrophosphate (28.4 mu mol min(-1) mg(-1)). The hydrolysis of ATP and PNPP by solubilized enzyme exhibited ''Michaelian'' kinetics with K-0.5 = 70 and 979 mu M, respectively. For pyrophosphate, K-0.5 was 128 mu M and site-site interactions were observed (n = 1.4). Magnesium ions were stimulatory (K-d = 1.5 mM) but zinc ions were powerful non-competitive inhibitors (K-d = 6.2 mu M) of solubilized enzyme. Treatment of solubilized alkaline phosphatase with Chellex 100 reduced the original PNPPase activity to 5%. Cobalt (K-0.5 = 10.1 mu M), magnesium (K-0.5 = 29.5 mu M) and manganese ions (K-0.5 = 5 mu M) restored the activity of the apoenzyme with positive cooperativity, suggesting that phosphatidylinositol-specific phospholipase C-solubilized alkaline phosphatase is a metalloenzyme. The stimulation of the apoenzyme by calcium ions (K-0.5 = 653 mu M) was lower than that observed for the other ions (26%) and exhibited site-site interactions (n = 0.7). Zinc ions had no effect on the apoenzyme of the solubilized enzyme.

Temperature dependence of fractal dimension of grain boundary region in SnO2 based ceramics

Fractal dimensions of grain boundary region in doped SnO2 ceramics were determined based on previously derived fractal model. This model considers fractal dimension as a measure of homogeneity of distribution of charge carriers. Application of the derived fractal model enables calculation of fractal dimension using results of impedance spectroscopy. The model was verified by experimentally determined temperature dependence of the fractal dimension of SnO2 ceramics. Obtained results confirm that the non-Debye response of the grain boundary region is connected with distribution of defects and consequently with a homogeneity of a distribution of the charge carriers. Also, it was found that C-T-1 function has maximum at temperature at which the change in dominant type of defects takes place. This effect could be considered as a third-order transition.

Exact boundary control for the wave equation in a polyhedral time-dependent domain

We establish exact boundary controllability for the wave equation in a polyhedral domain where a part of the boundary moves slowly with constant speed in a small interval of time. The control on the moving part of the boundary is given by the conormal derivative associated with the wave operator while in the fixed part the control is of Neuman type. For initial state H-1 x L-2 we obtain controls in L-2. (C) 1999 Elsevier B.V. Ltd. All rights reserved.

Linear analysis of building floor structures by a BEM formulation based on Reissner's theory

In this work, the plate bending formulation of the boundary element method (BEM) based on the Reissner's hypothesis is extended to the analysis of zoned plates in order to model a building floor structure. In the proposed formulation each sub-region defines a beam or a slab and depending on the way the sub-regions are represented, one can have two different types of analysis. In the simple bending problem all sub-regions are defined by their middle surface. on the other hand, for the coupled stretching-bending problem all sub-regions are referred to a chosen reference surface, therefore eccentricity effects are taken into account. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composed structure as a single body. The bending and stretching values defined on the interfaces are approximated along the beam width, reducing therefore the number of degrees of freedom. Then, in the proposed model the set of equations is written in terms of the problem values on the beam axis and on the external boundary without beams. Finally some numerical examples are presented to show the accuracy of the proposed model.

Ferroelectric state analysis in grain boundary of Na0.85Li0.15NbO3 ceramic

The electric and dielectric properties of the grain boundary of Na0.85Li0.15NbO3 lead-free ferroelectric-semiconductor perovskite were investigated. The impedance spectroscopy was carried out as a function of a thermal cycle. The sodium lithium niobate was synthesized by a chemical route based on the evaporation method. Dense ceramic, relative density of 97%, was prepared at 1423 K for 2 h in air atmosphere. ac measurements were carried out in the frequency range of 5 Hz-13 MHz and from 673 to 1023 K. Theoretical adjust of the impedance data was performed to deriving the electric parameters of the grain boundary. The electric conductivity follows the Arrhenius law, with activation energy values equal to 1.55 and 1.54 eV for heating and cooling cycle, respectively. The nonferroelectric state of the grain boundary and its correlation with symmetry are discussed in the temperature domain. (C) 2003 American Institute of Physics.

KINETIC-PROPERTIES OF OSSEOUS PLATE ALKALINE-PHOSPHATASE FROM DIABETIC RATS

1. Increased levels of bone alkaline phosphatase activity were observed in diabetic rats. These animals exhibited impaired bone development without concomitant alterations of the sequence of cellular transformations.2. Alkaline phosphatase activity was delayed in diabetic rats but the kinetic parameters for the hydrolysis of p-Nitrophenylphosphate (PNPP) were virtually the same observed for controls (N = 1.2 and K0.5 = 43 muM).3. Alkaline phosphatase from diabetic rats had a better affinity (K0.5 = 38 muM) for magnesium ions than controls (K0.5 = 9 1 muM).4. Zinc ions affected alkaline phosphatase activity from control and diabetic rats in the same way (K0.5 = 10 muM).

Formation of beta-nickel hydroxide plate-like structures under mild conditions and their optical properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Optimal control problem for deflection plate with crack

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A BEM formulation based on Reissner's theory to perform simple bending analysis of plates reinforced by rectangular beams

In this work, the plate bending formulation of the boundary element method (BEM), based on the Reissner's hypothesis, is extended to the analysis of plates reinforced by rectangular beams. This composed structure is modelled by a zoned plate, being the beams represented by narrow sub-regions with larger thickness. The integral equations are derived by applying the weighted residual method to each sub-region, and summing them to get the equation for the whole plate. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composed structure as a single body. In order to decrease the number of degrees of freedom, some approximations are considered for both displacements and tractions along the beam width. The accuracy of the proposed model is illustrated by simple examples whose exact solution are known as well as by more complex examples whose numerical results are compared with a well-known finite element code.

Fine structure of the boundary tissue of the seminiferous tubuli of the vampire bat (Desmodus rotundus, G.; Microchiroptera).

Structurally the boundary tissue of the vampire bat seminiferous tubuli showed 2 to 5 layers of connective tissue in which elongated contractile cells and lamellar and/or fibrillar collagen were noticed. This boundary tissue forms the seminiferous tubular lamina propria. Its structure was more complex around the seminiferous tubuli near the Capsula testicularis than between the adjacent and contiguous tubuli into the testicular lobuli. The whole ultrastructural organization of the seminiferous lamina propria was described here.

Numerical simulation of viscous three-dimensional flow over aerospace vehicles using Euler/boundary-layer zonal approach

This paper presents a viscous three-dimensional simulations coupling Euler and boundary layer codes for calculating flows over arbitrary surfaces. The governing equations are written in a general non orthogonal coordinate system. The Levy-Lees transformation generalized to three-dimensional flows is utilized. The inviscid properties are obtained from the Euler equations using the Beam and Warming implicit approximate factorization scheme. The resulting equations are discretized and approximated by a two-point fmitedifference numerical scheme. The code developed is validated and applied to the simulation of the flowfield over aerospace vehicle configurations. The results present good correlation with the available data.

Approximate solution for non-Darcy transient film condensation in a porous medium

The problem of non-darcian transient film condensation adjacent to a vertical flat plate embedded in a porous medium has been considered. The governing equation for the boundary layer thickness was obtained by an integral method and solved approximately by the method of integral relations. It is shown that the results are in good agreement with those obtained exactly by the method of characteristics.