To review the use of a new resin-dentin bonding model called the macro-hybrid layer, to quantify resin uptake and matrix shrinkage during resin infiltration and solvent evaporation. A secondary ...purpose was to introduce the concept of ethanol-wet bonding where water-saturated acid-etched dentin is exchanged with ethanol to create ethanol-saturated dentin. Adhesive monomers seem to penetrate ethanol-saturated dentin more thoroughly than water-saturated dentin.
Abstract Objectives This study evaluated the kinetics of water uptake and percent conversion in neat versus ethanol-solvated resins that were formulated to be used as dental bonding agents. Methods ...Five methacrylate-based resins of known and increasing hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Resins were evaluated as neat bonding agents (100% resin) or they were solvated with absolute ethanol (95% resin/5% ethanol or 85% resin/15% ethanol). Specimens were prepared by dispensing the uncured resin into a circular mold (5.8 mm × 0.8 mm). Photo-activation was performed for 80 s. The water sorption/diffusion/solubility was gravimetrically evaluated, while the degree of conversion (DC) was calculated by Fourier-transform infrared spectroscopy. Results Water sorption increased with the hydrophilicity of the resin blends. In general, the solvated resins exhibited significantly higher water sorption, solubility and water diffusion coefficients when compared to their corresponding neat versions ( p < 0.05). The only exception was resin R1, the least hydrophilic resin, in which neat and solvated versions exhibited similar water sorption ( p > 0.05). Addition of ethanol increased the DC of all resins tested, especially of the least hydrophilic, R1 and R2 ( p < 0.05). Despite the increased DC of ethanol–solvated methacrylate-based resins, it occurs at the expense of an increase in their water sorption/diffusion and solubility values. Significance Negative effects of residual ethanol on water sorption/solubility appeared to be greater as the hydrophilicity of the resin blends increased. That is, the use of less hydrophilic resins in dental adhesives may create more reliable and durable bonds to dentin.
Objectives. This study examined the null hypothesis that there is no difference between the effect of a one versus two-layer applications of Prompt L-Pop (3M ESPE, Seefeld, Germany) to sound, abraded ...human coronal dentine.
Methods. In group I, the mixed adhesive was applied for 15
s, and light-cured for 10
s. In group II, after light-curing the first layer, the adhesive was re-applied and light-cured. Specimens bonded with a hybrid composite were sectioned into beams for microtensile bond strength evaluation. Additional teeth from each group were bonded similarly using a lining composite for transmission electron microscopy examination of the resin–dentine interfaces, and nanoleakage evaluation using ammoniacal silver nitrate.
Results. A significant difference (
p<0.001) was detected between microtensile bond strengths in the two groups. Stained, demineralized sections revealed 3–5
μm thick hybrid layers in both groups. An electron-lucent layer between 7 and 20
μm thick was present between the adhesive and the overlying composite. This layer was absent from the interfaces after removal with ethanol before composite placement. The use of a single application in group I resulted in the direct contact of the electron-lucent layer with the dentine surface and tubular orifices. In unstained, undemineralized sections used to evaluate nanoleakage, silver deposits were found mostly in the hybrid layer in group II, but throughout the entire adhesive layer in group I.
Conclusion. Bonding of this unfilled all-in-one adhesive to dentine may be improved by application of a second adhesive layer after light-curing the first layer. This ensures that the exposed dentine surface and dentinal tubules are coated with adhesive that is adequately polymerized.
Objectives. The aim of this study was to test the null hypothesis that the tensile properties of demineralized dentin are not influenced by the hydrogen bonding ability of anhydrous polar solvents.
...Methods. Dentin disks 0.5
mm thick were prepared from mid-coronal dentin of extracted, unerupted, human third molars. ‘I’ beam and hour-glass shaped specimens were prepared from the disks, the ends protected with nail varnish and the central regions completely demineralized in 0.5
M EDTA for 5 days. Ultimate tensile stress (UTS) and low-strain apparent modulus of elasticity (
E) were determined with the specimens immersed for 60
min in water, methanol, HEMA, acetone or air prior to testing in those same media. Apparent moduli of elasticity were measured on the same specimens in a repeated measures experimental design. The results were analyzed with a one-way ANOVA on ranks, followed by Dunn's test at
α=0.05. Regression analysis examined the relationship between UTS or
E and Hansen's solubility parameter for hydrogen bonding (
δ
h) of each solvent.
Results. The UTS of demineralized dentin in water, methanol, HEMA, acetone and air was 18(7), 29(7), 31(6), 41(13) and 146(27)
MPa,
x
̄
(
SD),
n=10. Low-strain
E for the same media were 11(7), 43(12), 79(21), 132(31) and 253(115)
MPa. Regression analysis of UTS vs
δ
h revealed a significant (
p<0.0005,
r=−0.69,
R
2=0.48) inverse, exponential relationship. A similar inverse relationship was obtained between low-strain
E vs
δ
h (
p<0.0001,
r=−0.93,
R
2=0.86).
Significance. The tensile properties of demineralized dentin are dependent on the hydrogen bonding ability of polar solvents (
δ
h). Solvents with low
δ
h values may permit new interpeptide H-bonding in collagen that increases its tensile properties. Solvents with high
δ
h values prevent the development of these new interpeptide H-bonds.
Successful fire exclusion in the 20th century has created severe fire problems across the West. Not every forest is at risk of uncharacteristically severe wildfire, but drier forests are in need of ...active management to mitigate fire hazard. We summarize a set of simple principles important to address in fuel reduction treatments: reduction of surface fuels, increasing the height to live crown, decreasing crown density, and retaining large trees of fire-resistant species. Thinning and prescribed fire can be useful tools to achieve these objectives. Low thinning will be more effective than crown or selection thinning, and management of surface fuels will increase the likelihood that the stand will survive a wildfire. Five empirical examples of such treatment are discussed: Hayfork fires, California, 1987; Tyee fire, Washington, 1994; Megram fire, California, 1999; Hayman fire, Colorado, 2002; and the Cone fire, California, 2002. Applying treatments at an appropriate landscape scale will be critical to the success of fuel reduction treatments in reducing wildfire losses in Western forests.
Permeability of demineralized dentin to HEMA Pashley, D.H.; Zhang, Y.; Agee, K.A. ...
Dental materials,
2000, 2000-Jan, 2000-1-00, 20000101, Letnik:
16, Številka:
1
Journal Article
Recenzirano
Objectives: The objectives of this study were to develop a macromodel of the demineralized layer of dentin that is formed after acid-etching, and to determine if the amount of HEMA uptake was ...responsive to air drying. The hypothesis that was tested was that HEMA uptake by demineralized dentin depends upon the degree of expansion of the collagen fibril network.
Methods: Dentin cubes (2×2×2
mm) were prepared in coronal dentin from extracted unerupted human third molars. They were incubated in 100% HEMA for up to 1000
min and then removed and blotted free of excess adherent HEMA. The HEMA taken up by each cube was extracted in 2
ml of water for 1
hr with shaking. This was repeated and the extracts combined. HEMA was quantitated spectrophometrically. The dentin cubes were then demineralized in 0.5
M EDTA for 10
days and the HEMA uptake remeasured at 1, 10, 100 and 1000
min. Then the cubes were air-dried and the HEMA uptake remeasured. After re-expanding the specimens in water, the cubes were stiffened in ascending concentrations of acetone of 100%, then allowed to air dry again in a more expanded state, and HEMA uptake was remeasured. Finally, after rehydration, the dentin cubes were “acid-etched” for 1 or 10
min with 37
wt% phosphoric acid and HEMA uptake remeasured.
Results: Before demineralization, the dentin took up little HEMA (ca. 4.8×10
−7
moles min
−3) compared to after demineralization when the uptake for 10, 100 and 1000
min was 27.4, 43.8 and 51.4×10
−3
moles mm
−3, respectively. Acid etching for 1 or 10
min had no effect on HEMA uptake. Air drying produced a 72% volumetric shrinkage but a 97% reduction in uptake. When the demineralized matrix was stiffened in acetone prior to air-drying, the volumetric shrinkage was only 27% and the HEMA uptake only fell 16% compared to the wet, fully expanded condition.
Significance: The results support the hypothesis that the uptake of HEMA by demineralized dentin depends on the degree of expansion of the dentin matrix.
Managing Forests and Fire in Changing Climates Stephens, S. L.; Agee, J. K.; Fulé, P. Z. ...
Science (American Association for the Advancement of Science),
10/2013, Letnik:
342, Številka:
6154
Journal Article
Recenzirano
With projected climate change, we expect to face much more forest fire in the coming decades. Policy-makers are challenged not to categorize all fires as destructive to ecosystems simply because they ...have long flame lengths and kill most of the trees within the fire boundary. Ecological context matters: In some ecosystems, high-severity regimes are appropriate, but climate change may modify these fire regimes and ecosystems as well. Some undesirable impacts may be avoided or reduced through global strategies, as well as distinct strategies based on a forest's historical fire regime.
Random-Phase Approximation Methods Chen, Guo P; Voora, Vamsee K; Agee, Matthew M ...
Annual review of physical chemistry,
05/2017, Letnik:
68, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Random-phase approximation (RPA) methods are rapidly emerging as cost-effective validation tools for semilocal density functional computations. We present the theoretical background of RPA in an ...intuitive rather than formal fashion, focusing on the physical picture of screening and simple diagrammatic analysis. A new decomposition of the RPA correlation energy into plasmonic modes leads to an appealing visualization of electron correlation in terms of charge density fluctuations. Recent developments in the areas of beyond-RPA methods, RPA correlation potentials, and efficient algorithms for RPA energy and property calculations are reviewed. The ability of RPA to approximately capture static correlation in molecules is quantified by an analysis of RPA natural occupation numbers. We illustrate the use of RPA methods in applications to small-gap systems such as open-shell
d
- and
f
-element compounds, radicals, and weakly bound complexes, where semilocal density functional results exhibit strong functional dependence.
Our experience with the Sauve-Kapandji procedure for reconstruction of the rheumatoid distal radioulnar joint is reported. Twenty-one wrists in 17 patients were followed for an average of 39 months ...postoperatively. Average range of motion at follow-up evaluation was pronation to 78 degrees and supination to 86 degrees. X-ray films demonstrated that significant ulnarward and palmarward translocation of the carpus was prevented. The Sauve-Kapandji procedure provides a stable ulnar side support in the rheumatoid wrist with distal radioulnar degeneration.
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