pH dependence of uranyl retention in a quartz/solution system: an XPS study.

We have investigated the pH dependence of U(VI) retention in quartz/10(-4) M uranyl solution systems, under conditions favoring formation of polynuclear aqueous species and of colloids of amorphous schoepite as U(VI) solubility-limiting phases. X-ray photoelectron spectroscopy was used to gain insights into the coordination environments of sorbed/precipitated uranyl ions in the centrifuged quartz samples. The U4f XPS spectra made it possible to identify unambiguously the presence of two uranyl components. A high binding energy component, whose relative proportion increases with pH, exhibits the U4f lines characteristic of a reference synthetic metaschoepite. Such a high binding energy component is interpreted as a component having a U(VI) oxide hydrate character, either as polynuclear surface oligomers and/or as amorphous schoepite-like (surface) precipitates. Its pH dependence suggests that a binding of polynuclear species at quartz surfaces and/or a formation of amorphous schoepite-like (surface) precipitates is favored when the proportion of aqueous polynuclear species increases. A second surface component exhibits binding energies for the U4f core levels at values significantly lower (DeltaE(b)=1.2 eV) than for metaschoepite, evidencing uranyl ions in a distinct coordination environment. Such a low binding energy component may be attributed to monomeric uranyl surface complexes on the basis of published EXAFS data. Such a hypothesis is supported by a major contribution of the low binding energy component to the U4f XPS spectra of reference samples for uranyl sorbed on quartz from very acidic 10(-3) M uranyl solutions where UO(2)(2+) ions predominate.

Analysis of sealing vs tensile bond strength of eight adhesive restorative material systems.

PURPOSE: Using a simulated perfusion system, the intent was to determine: 1) the sealing ability of eight restorative materials (five composite resins and three compomers) used together with their corresponding dentin bonding systems, 2) their tensile bond strength, and 3) the correlation (if any) between both parameters. MATERIALS AND METHODS: Permeability in crown segments from sound human third molars (n = 140) subjected to simulated perfusion (32 cm of distilled water) was measured before and after restoring with each material, and the percentage of decrease in permeability (PPD) was recorded. Specimens were later subjected to tensile tests to determine the tensile bond strength (TBS) of the interface. Finally, parameters were analyzed for correlation. RESULTS: For the eight adhesive systems, the percentage of reduction in permeability was relatively high [mean in %, (SD)]: F2000 93.6 (5.7), SB1 88.6 (11.3), SSC 86.0 (5.7), PB20 81.1 (15.9), COM 77.5 (10.8), OPTS 75.3 (20.6), DYR 73.7 (12.7), SSPR 65.5 (19.8). TBS values were relatively low [mean (SD)], in MPa: F2000 1.8 (0.7), SB1 4.9 (1.4), SSC 2.6 (1.4), PB20 4.3 (1.2), COM 2.4 (1.1), OPTS 4.5 (1.7), DYR 1.6 (0.6), SSPR 4.2 (1.5). We could not demonstrate any statistically significant correlation between both parameters for these results (maximum significance [F2000]: r = 0.39, p = 0.206). CONCLUSION: No material completely ceased to filtrate through the interface. The low TBS values were probably due to the large size of adhesive areas. No significant correlation was found between PPD and TBS for the materials tested. There was a statistically significant relationship (r2 = 0.063, p = 0.018) between TBS and TBA (total bonded area), described by the equation TBS = 5.9 - 0.03.TBA.

Sealing and dentin bond strengths of adhesive systems.

The objectives of this research were (1) to analyze the variations of the permeability of dentin after restoration with two polyacid-modified resin composites (Compoglass, Dyract) and four single-bottle adhesives (Prime & Bond 2.0, Syntac Single Component, OptiBond Solo, and Single Bond--Scotch Bond 1 in Europe--immediately (approximately 1 hour) after insertion. A perfusion system with distilled water was used at a pressure of 32.5 cm of water; (2) to study the bond strength of their interfaces; and (3) to find the correlation, if any, between both parameters. None of the materials used produced a complete cessation in fluid filtration. Tensile bond strengths were very low (maximum: P&B = 3.96 MPa) probably because of the very large bonding surfaces used (mean bonded surface area = 88.8 mm2). No significant correlation was found between tensile bond strength and the sealing ability for any material.

[Evaluation in experimental animals of a mathematical model of foreseeing variations in values of stable glycosylated hemoglobin]. / Valutazione sull'animale da esperimento di un modello matematico per la previsione delle variazioni dei valori di emoglobina glicosilata stabile.

Assay of glycosylated hemoglobin provides reliable information on metabolic control in diabetes mellitus over a period of about 90 days. This is why it is currently used as a parameter of blood glucose control in diabetic patients. However, at present little is known about the kinetics of stable glycosylated hemoglobin variations as a result of circadian changes in blood glucose level. The authors describe a mathematical model which allows to foresee glycosylated hemoglobin variability as a result of alterations of blood glucose equilibrium.