Fracture strength of bovine incisors after intra-radicular treatment with MTA in an experimental immature tooth model

Aim To evaluate, using an experimental immature tooth model, the fracture resistance of bovine incisors submitted to different reinforcement treatments with mineral trioxide aggregate (MTA).Methodology An immature tooth model was created by sectioning the coronal and apical portions of 40 bovine incisors 8 mm above and 12 mm below the cementoenamel junction. The root canals were irrigated with 1.0% sodium hypochlorite. They were enlarged both coronally and apically using number 703 carbide burs (ISO: 500-104-168-007-021) and their internal diameter was standardized to 2.1 mm. The specimens were assigned to four groups (n = 10): GI-control (without filling); GII-apical MTA plug + filling with gutta-percha and endodontic sealer; GIII-filling with MTA; GIV-apical MTA plug + filling with MTA + metallic post (Reforpost I). A polyether impression material was used to simulate the periodontal ligament. The specimens were submitted to a compressive load at a crosshead speed of 0.5 mm min(-1) in a servo-hydraulic universal testing machine (MTS 810) applied at 45 degrees to the long axis of the tooth until failure. Data were submitted to statistical analysis by the Kruskal-Wallis test at 5% significance level.Results GIV presented the highest fracture resistance (32.7N) and differed significantly from the other groups (P < 0.05). No statistically difference was found between GII (16.6N) and GIII (23.4N) (P > 0.05). GIII had a significantly higher fracture resistance than GI (P < 0.05).Conclusions the use of MTA + metallic post as an intra-radicular reinforcement treatment increased the resistance to fracture of weakened bovine teeth in an experimental immature tooth model.

Persistence and effectiveness of pyrethroids in plastic strips against Varroa jacobsoni (Acari : Varroidae) and mite resistance in a mediterranean area

An apiary trial was conducted in 1997 in Sardinia, Italy, to verify the effectiveness of fluvalinate in polyvinyl chloride strips and flumethrin in polyethylene strips against Varroa jacobsoni Oudemans. Two indices to evaluate the efficacy of the treatments were adopted: percentage change in mite infestation of worker-sealed brood cells considering only treated hives and percentage change in mite mortality, and the natural variation in mite populations recorded in control hives during the trial. All acaricide treatments reduced the level of mite infestation of both sealed brood and adult bees. However, their effectiveness was slightly reduced in comparison to previous studies because of mite resistance phenomena. Portions of polyethylene strips of flumethrin from treated hives were sampled weekly to determine acaricide persistence using gas chromatography. After 4 wk, a slight reduction (approximate to9%) of the active ingredient content was observed, A laboratory bioassay also was performed to establish the resistance of adult female mites to fluvalinate, Mites were sampled from the experimental apiary and from various Sardinian apiaries which had primarily been subjected to fluvalinate applications in plastic strips or wood inserts for years. Mite resistance varied from 0 to 96%, depending on the acaricide management adopted, the lowest resistance level occurred in an apiary where pyrethroids had never been used, whereas the highest level occurred in an apiary with intensive use of fluvalinate in wood inserts.

Femtosecond nonlinear optical properties of tellurite glasses

The third-order nonlinear optical properties of tellurite glasses with different compositions were investigated in the femtosecond regime at 810 nm. Using the I-scan technique, positive nonlinear refractive indices of similar to 10(-15) cm(2)/W were measured. The authors also determined that nonlinear absorption was negligible for all studied samples. This result, added to their good chemical stability, indicates that tellurite glasses are promising materials for ultrafast photonic applications. (c) 2006 American Institute of Physics.

Atributos físicos do solo e produtividade do milho sob sistemas de manejo e adubações

No-tillage system is an efficient technique in control of soil erosion, when compared with conventional tillage, however, some studies indicate higher compaction under no-tillage, mainly in the surface layer. Strategies that increase the organic matter content, as crop rotation and organic fertilization, can be used to solve the soil compaction. The aim of this study was to evaluate the effect of soil managements (crop succession and crop rotation) and fertilization (organic, mineral and organic-mineral) in the physical properties of the soil, under no-tillage system, from 2006 to 2008. The evaluations were carried out in February 2007, after the summer corn harvest, and in September 2008, after the winter corn harvest. Crop rotation decreased the soil density and soil resistance to penetration and increased the macroporosity and total porosity. The use of organic sources of fertilization did not affect any of the physical attributes of soil. The yield of summer corn was highest in succession crop and mineral fertilization, however, in the winter, there was no difference between the soil managements and among the fertilizations.

Preparation, characterization and spectroscopy of the europium diphenylphosphinate complex

The purpose of this work is to study the preparation and spectroscopic behavior of the europium diphenylphosphinate complex -Eu(DPP)3. Elemental and thermogravimetric analysis, powder X-ray diffractometry, and infrared spectroscopy were applied to characterize the formula of the final product and the sixfold coordination of the Eu3+ ion. Excitation and emission spectra have been recorded at liquid nitrogen and room temperatures. The 5D0→7F2 transition intensity decreases when T decreases in comparison to the 5D0→7F1 transition intensity. Molecular mechanic calculations were developed in order to obtain the spatial coordinates of the Eu3+ and ligand ions. The simple overlap model was used to calculate the total splitting of the 5D0→7F1 transition, 5D0→7F0/5D 0→7F2 ntensity ratio and the intensity parameters, Ωλ (λ=2 and 4). Good agreements between theoretical predictions and experimental results have been obtained with g=2/3 as the effective charge and α=0.8×10-24 cm3 as the isotropic polarizability of the oxygen. © 1998 Elsevier Science S.A.

A comparison of molar root canal preparation using stainless-steel and nickel-titanium instruments

Fifty-four extracted human mandibular molars were embedded and sectioned at two levels. The reassembled mesial root canals were prepared with stainless-steel hand K-files (Flexofiles) and either Nitiflex or Mity nickel-titanium hand K-files using a push-pull anticurvature filing technique. Each of the three experimental groups contained 36 mesial canals randomly distributed. Superimposed pre- and postinstrumentation cross-sectional root images were magnified using a stereomicroscope and transferred to a computer for measurement and statistical analysis. The direction and extent of canal center movement were evaluated. At the apical level, the groups produced no significant difference of direction of canal center movement. In cervical sections, all groups tended to move in a distolingual direction. The three groups, however, produced no significant difference in the cervical sections in the extent of canal center movement. In apical sections, Nitiflex produced the least canal center movement. Copyright © 1999 by The American Association of Endodontists.

Genetic variability of Brazilian strains of the Microcystis aeruginosa complex (Cyanobacteria/Cyanophyceae) using the phycocyanin intergenic spacer and flanking regions (cpcBA)

The genetic and morphological variability among 15 Brazilian strains of Microcystis aeruginosa (Kütz.) Kütz. collected from four locations was examined and compared with several reference strains of M. aeruginosa, M. viridis (A. Br.) Lemm. and M. wesenbergii (Kom.) Kom. in Kondr. Brazilian strains were classified by morphological features and by comparison of the nucleotide sequences of the cpcBA intergenic spacer and flanking regions. Our results indicate that Brazilian strains classified as M. aeruginosa are phylogenetically diverse compared with reference strains of M. aeruginosa and that the current taxonomy underestimates genetic diversity within M. aeruginosa. The data also demonstrate that morphological criteria alone are inadequate to characterize Microcystis species. Although colonial characters were shown to vary considerably in culture, some genetic lineages demonstrated consistent cellular diameter ranges, indicating that cell size has value as a taxonomic character. The detection of six M. aeruginosa genotypes in a single water body indicates that morphological approaches can also seriously underestimate the diversity of Microcystis bloom populations.

Progress on holographic techniques to study photo-chemical reactions in solid state

In this paper it is presented recent developments in the heterodyne detection holographic techniques for studding photosensitive materials. The actual state of the technique allows simultaneous and independent measurement of the refractive index and of the absorption coefficient changes in photosensitive materials and their use to self-stabilize the fringe pattern. The modeling of the measured signal together with the fringe stabilization allow the long term-fitting of the optical properties and the study the photosensitive materials close to the saturation.

Effect of thermal treatments on tensile strength of commercially cast pure titanium and Ti-6Al-4V alloys

Heating titanium structures is assumed to relieve tensions induced by the casting process as well as possibly optimizing some mechanical properties. The aim of this investigation was to evaluate the effect of thermal treatments on tensile strength of commercially pure titanium (CP Ti) and Ti-6Al-4V alloy. Thirty dumbbell rods, with diameters of 3.0 mm at the central segment and lengths of 42 mm, were cast for each metal using the Rematitan System. CP Ti and Ti-6Al-4V specimens were randomly divided into three groups of ten: a control group that received no thermal treatment and two test groups. One (T1) was heated at 750°C for 2 h and the other (T2) was annealed at 955°C for 1 h and aged at 620°C for 2 h. Tensile strength was measured with a universal testing machine (MTS model 810). Tensile strength means and standard deviations were statistically compared using a Kruskal-Wallis test at a α = 0.05 significance level. No statistically significant differences in tensile strength were observed among CP Ti groups. For the Ti-6Al-4V alloy, the control and T1 groups revealed statistically higher tensile strengths when compared to the T2 group, with no significant difference between the control and T1 groups. © 2005 Springer Science + Business Media, Inc.

Gravity and the quantum: Are they reconcilable?

General relativity and quantum mechanics are not consistent with each other. This conflict stems from the very fundamental principles on which these theories are grounded. General relativity, on one hand, is based on the equivalence principle, whose strong version establishes the local equivalence between gravitation and inertia. Quantum mechanics, on the other hand, is fundamentally based on the uncertainty principle, which is essentially nonlocal. This difference precludes the existence of a quantum version of the strong equivalence principle, and consequently of a quantum version of general relativity. Furthermore, there are compelling experimental evidences that a quantum object in the presence of a gravitational field violates the weak equivalence principle. Now it so happens that, in addition to general relativity, gravitation has an alternative, though equivalent, description, given by teleparallel gravity, a gauge theory for the translation group. In this theory torsion, instead of curvature, is assumed to represent the gravitational field. These two descriptions lead to the same classical results, but are conceptually different. In general relativity, curvature geometrizes the interaction while torsion, in teleparallel gravity, acts as a force, similar to the Lorentz force of electrodynamics. Because of this peculiar property, teleparallel gravity describes the gravitational interaction without requiring any of the equivalence principle versions. The replacement of general relativity by teleparallel gravity may, in consequence, lead to a conceptual reconciliation of gravitation with quantum mechanics. © 2006 American Institute of Physics.

Effect of the association of nystatin with a tissue conditioner on its ultimate tensile strength

Purpose: This study evaluated the ultimate tensile strength of a tissue conditioner without nystatin incorporation (GI - control group) and the same tissue conditioner modified by the addition of nystatin in two concentrations: GII - 500,000 International Units (U) and GIII - 1,000,000 U, in which each milligram of the medicament corresponded to 6079 U. Materials and Methods: Dumbbell-shaped specimens (N = 7) with a central cross-sectional area of 33 × 6 × 3 mm were produced for the three experimental groups. After polymerization following manufacturer's instructions, specimens were immersed in distilled water at 37°C for either 24 hours or 7 days and then tested in tension in the MTS 810 at 40 mm/minute. Data were analyzed by two-way ANOVA followed by Tukey's test, at 95% level of confidence. Results: The means (force-grams (gf) ± standard deviation) of the ultimate tensile strength were: GI - 634.29 ± 122.80; GII - 561.92 ± 133.56; and GIII - 547.30 ± 73.47 for 24-hour storage, and GI - 536.68 ± 54.71; GII - 467.50 ± 143.51; and GIII - 500.62 ± 159.76 for 7-day storage. There were no statistically significant differences among the three experimental groups (p > 0.05). The ultimate tensile strength means of all experimental groups after 7 days were significantly lower than those observed after 24 hours (p = 0.04). Conclusions: The results of this study suggest that the addition of nystatin into the tissue conditioner investigated in concentrations below 1,000,000 U did not affect its ultimate tensile strength. Copyright © 2006 by The American College of Prosthodontists.

A multicommuted flow-based system for hydrogen peroxide determination by chemiluminescence detection using a photodiode

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow-cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III). The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2-210 μmol l-1 H2O2 with a LD of 1.8 μmol l-1 H2O2 and coefficient of variations smaller than 0.8% for 1.0×10-5 mol l-1 and 6.8×10-5 mol l-1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 μg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved. Copyright © Taylor & Francis Group, LLC.

Influence of the final temperature of investment healting on the tensile strength and Vickers hardness of CP TI and TI-6AL-4V alloy

The aim of the work was to evaluate the influence of the temperature of investment healting on the tensile strength and Vickers hardness of CP Ti and Ti-6Al-4V alloy casting. Were obtained for the tensile strength test dumbbell rods that were invested in the Rematitan Plus investment and casting in the Discovery machine cast. Thirty specimens were obtained, fiftten to the CP Titanium and fifteen to the Ti-6Al-4V alloy, five samples to each an of the three temperatures of investment: 430°C (control group), 480°C and 530°C. The tensile test was measured by means of a universal testing machine, MTS model 810, at a strain of 1.0 mm/min. After the tensile strenght test the specimens were secctioned, embedded and polished to hardness measurements, using a Vickers tester, Micromet 2100. The means values to tensile tests to the temperatures 430°C, 480 and 530: CP Ti (486.1 - 501.16 - 498.14 -mean 495.30 MPa) and Ti-6Al-4V alloy (961.33 - 958.26 - 1005.80 - mean 975.13 MPa) while for the Vickers hardness the values were (198.06, 197.85, 202.58 - mean 199.50) and (352.95, 339.36, 344.76 - mean 345.69), respectively. The values were submitted to Analysis of Variance (ANOVA) and Tukey' s Test that indicate differences significant only between the materials, but not between the temperature, for both the materias. It was conclued that increase of the temperature of investment its not chance the tensile strength and the Vickers hardness of the CP Titanium and Ti-6Al-4V alloy.

Tensile bond strength of self-etching versus total-etching adhesive systems under different dentinal substrate conditions

The use of acid etchants to produce surface demineralization and collagen network exposure, allowing adhesive monomers interdiffusion and consequently the formation of a hybrid layer, has been considered the most efficient mechanism of dentin bonding. The aim of this study was to compare the tensile bond strength to dentin of three adhesive systems, two self-etching ones (Clearfil SE Bond - CSEB and One Up Bond F - OUBF) and one total-etching one (Single Bond - SB), under three dentinal substrate conditions (wet, dry and re-wet). Ninety human, freshly extracted third molars were sectioned at the occlusal surface to remove enamel and to form a flat dentin wall. The specimens were restored with composite resin (Filtek Z250) and submitted to tensile bond strength testing (TBS) in an MTS 810. The data were submitted to two-way ANOVA and Tukey's test (p = 0.05). Wet dentin presented the highest TBS values for SB and CSEB. Dry dentin and re-wet produced significantly lower TBS values when using SB. OUBF was not affected by the different conditions of the dentin substrate, producing similar TBS values regardless of the surface pretreatments.