New X-ray powder diffraction data and Rietveld refinement for Gd2O3 monodispersed fine spherical particles

Nominally pure Gd2O3 C-form structure from basic carbonate fine spherical particles and its differences concerning the XRD data among literature patterns using Rietveld method is reported. Gd2O3: Eu3+ from basic carbonate and Gd2O3 from oxalate were also investigated. All samples, except the one from oxalate precursor, are narrow sized, 100-200 nm. Only non-doped Gd2O3 from basic carbonate presents XRD data with smaller d(hkl) values than the literature ones. From Rietveld refinement, non-doped Gd2O3 from basic carbonate has the smallest crystallite size and from oxalate shows the greatest one. Also, the unit cell parameters indicate a plan contraction of the Gd2O3 from basic carbonate. The presence of Eu3+ increases crystallite size when basic carbonate precursor is used to prepare Gd2O3 and avoids plan contraction. The structural differences observed among Gd2O3 samples obtained are related to the type of precursor and to the presence or not of doping ion. (C) 2003 Elsevier B.V. (USA). All rights reserved.

Temperature rise in cavities prepared by high and low torque handpieces and Er : YAG laser

Objective The aim of this study was to compare intrapulpal temperature increases produced by a high-speed high-torque (speed-increasing) handpiece, a high-speed low-torque handpiece (air-turbine) and an Er: YAG (Erbium: Yttrium-Aluminum-Garnet) laser. Subject and methods Thirty bovine incisors were reduced to a dentine thickness of 2.0 mm. Class V preparations were prepared to a depth of 1.5 mm, measured with a caliper or by a mark on the burs. A thermocouple was placed inside the pulp chamber to determine temperature increases (C). Analysis was performed on the following groups (n = 10) treated with: G1, low-torque handpiece; G2, high-torque handpiece; and G3, Er: YAG laser (2.94 mu m at 250 mJ/4 Hz), all with water cooling. The temperature increases were recorded with a computer linked to the thermocouples. Results The data were submitted to ANOVA and Tukey statistical test. The average temperature rises were: 1.92 +/- 0.80 degrees C for G1, 1.34 +/- 0.86 degrees C for G2, and 0.75 +/- 0.39 degrees C for G3. There were significant statistical differences among the groups (p = 0.095). All the groups tested did not have a change of temperature that exceeds the threshold of 5.5 degrees C. Conclusion Temperature response to the low and high torque handpieces seemed to be similar, however the Er: YAG laser generated a lower temperature rise.

Spherical particles of phenolic resin treated with iron oxide

This paper describes the preparation and characterization of phenolic resins' thermospheres covered by a magnetic phase of iron oxide. The thermospheres were prepared by allowing phenol and formaldehyde to react under dispersion polymerization conditions and the iron oxide phase was incorporated in situ onto the phenolic resin particles by adding concentrated NH3 to FeCl2 in DMSO. This reaction was conducted at 70 degrees C under nitrogen atmosphere in a controlled temperature vessel, and the modified resin was isolated and dried in vacuo. Both pure and modified resins were characterized by DRX, TG- DTA, and MEV/ EDX. The modified particles were attracted by a magnetic field, indicating the fixation of magnetic iron oxide. No diffraction peaks were observed in DRX analysis; thermal analysis ( DTA) of both pure and modified resins presented exothermic events between 300 and 680 degrees C, and 300 and 570 degrees C, respectively, indicating the microstructure of the resin was modified after the treatment. Thermogravimetric analysis ( TGA) of the pure resin registered a 2.0% residue, compared to 8.0% for the modified resin. These residues correspond to about 7.0% of fixed iron oxide. MEV/ EDX analyses confirm the modification of the resins by the process of fixing iron oxide.

Non-leachable highly luminescent ordered mesoporous SiO2 spherical particles

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preparation and characterization of uniform, spherical particles of Y2O2S and Y2O2S:Eu

The preparation of spherical Y2O2S and Y2O2S:Eu particles using a solid-gas reaction of monodispersed precursors with elemental sulfur vapor under an argon atmosphere has been investigated. The precursors, undoped and doped yttrium basic carbonates, are synthesized by aging a stock solution containing the respective cation chloride and urea at 82-84 °C. Y2O2S and Y2O2S:Eu were characterized in terms of their composition, crystallinity and morphology by chemical analysis, X-ray powder diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The Eu-doped oxysulfide was also characterized by atomic absorption spectrophotometry and luminescence spectroscopy. The spherical morphology of oxysulfide products and of basic carbonate precursors suggests a topotatic inter-relationship between both compounds.

Preparation and characterization of spherical yttrium iron garnet via coprecipitation

The purpose of this work is to obtain spherical particles yttrium iron garnet (YIG) by coprecipitation technique. The spherical particles were obtained from either nitrate or chloride salt solutions by controlling the precipitation medium. Different agents of dispersion such as PVP and ammonium iron sulfate were used to optimize the shape and size of YIG. Samples were characterized by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The results show that the samples phase transition takes place at 850°C (orthorhombic phase) and at 1200°C (cubic phase). Spherical shape particles, with diameter of around 0.5 μm, present magnetization values close to the bulk value (26 emu g -1). © 2001 Elsevier Science B.V. All rights reserved.

Evaluation of marginal microleakage in Class II cavities: Effect of microhybrid, flowable, and compactable resins

Objective: The goal of the present study was to evaluate the microleakage on the cementum/dentin and enamel surfaces in Class II restorations, using different kinds of resin composite (microhybrid, flowable, and compactable). Method and materials: Forty human caries-free molars were extracted and selected. Eighty Class II standardized cavities were made in the cervical wall at the cementoenamel junction (CEJ) and at the mesial and distal surfaces. The teeth were divided into four groups: G1 - adhesive system + microhybrid resin composite Z100; G2 - adhesive system + compactable resin composite Prodigy Condensable; G3 - adhesive system + flowable resin composite Revolution + Z100 resin composite; G4 - adhesive system + Revolution fluid resin + compactable resin composite Prodigy Condensable. The adhesive system used in this study was Scotchbond Multi-Purpose Plus. The specimens were thermocycled in baths of 5°C and 55°C for 1,000 cycles and immersed in 50% silver nitrate solution. The specimens then were sectioned and evaluated on degree of dye penetration. Results: The results were evaluated using the nonparametric Kruskall-Wallis test, which showed a statistically significant difference between groups G1 and G4, G2 and G4, and G3 and G4. Conclusions: None of the materials was able to eliminate the marginal microleakage at the cervical wall; the application of a low-viscosity resin composite combined with a compactable resin composite significantly decreased the microleakage.

Cutting characteristics of dental diamond burs made with CVD technology

The aim of this study was to determine the cutting ability of chemical vapor deposition (CVD) diamond burs coupled to an ultrasonic dental unit handpiece for minimally invasive cavity preparation. One standard cavity was prepared on the mesial and distal surfaces of 40 extracted human third molars either with cylindrical or with spherical CVD burs. The cutting ability was compared regarding type of substrate (enamel and dentin) and direction of handpiece motion. The morphological characteristics, width and depth of the cavities were analyzed and measured using scanning electron micrographs. Statistical analysis using the Kruskal-Wallis test (p < 0.05) revealed that the width and depth of the cavities were significantly greater when they were prepared on dentin. Wider cavities were prepared when the cylindrical CVD bur was used, and deeper cavities resulted from preparation with the spherical CVD bur. The direction of handpiece motion did not influence the size of the cavities, and the CVD burs produced precise and conservative cutting.

The Dirac-Hestenes equation for spherical symmetric potentials in the spherical and Cartesian gauges

In this paper, using the apparatus of the Clifford bundle formalism, we show how straightforwardly solve in Minkowski space-time the Dirac-Hestenes equation - which is an appropriate representative in the Clifford bundle of differential forms of the usual Dirac equation - by separation of variables for the case of a potential having spherical symmetry in the Cartesian and spherical gauges. We show that, contrary to what is expected at a first sight, the solution of the Dirac-Hestenes equation in both gauges has exactly the same mathematical difficulty. © World Scientific Publishing Company.

Biocompatibility of resin-based dental materials applied as liners in deep cavities prepared in human teeth

Background: Since only a few data have been published concerning the effects of resinous dental materials on the pulp-dentin complex, the aim of this study was to evaluate the biocompatibility of resin-based materials applied as liners in deep cavities prepared in duman teeth. Methods: After preparing class V cavities, the following dental materials were applied on the axial walls: group 1, Vitrebond™ (VIT; 3M ESPE); group 2, Ultra-Blend® Plus™ (UBP; Untradent); and group 3, Clearfil™ SE Bond (CSEB; Kuraray). In group 4 (control), the hard-setting calcium hydroxide cement Dycal (CH; Caulk/Dentsply) was used. The teeth extracted at 7 days or between 30 and 85 days after the clinical procedures were processed for histological evaluation. Results: For all the experimental and control groups, most of specimens exhibited no pulpal response or slight inflammatory reaction associated with slight tissue disorganization at 7-day period. Moderate inflammatory pulpal response occurred only in one tooth (RDT = 262 μm) of group 3 in which transdentinal diffusion of resin components was observed. Conclusion: The resin-based dental cements VIT and UBP as well as the bonding agent CSEB presented acceptable biocompatibility when applied in deep cavities prepared in sound human teeth. © 2006 Wiley Periodicals, Inc.

Study of the potential of irregular shaped bodies and orbits around a non-spherical body

In the present work we show the expressions of the gravitational potential of homogeneous bodies with non-spherical three-dimensional shapes in order to study the trajectories around these bodies. The potentials of a prolate and an oblate ellipsoids with different values of semi-major axis are presented. Their results are validated with a test using a spherical body in order to guarantee the approximation of any body as a polyhedral model of the body. With these expressions we study trajectories of a point of mass around the three-dimensional bodies and the results indicated that there is a group of orbits around those bodies and the polyhedral form of the object does work very well. Copyright IAF/IAA. All rights reserved.

Analytical model for heterogeneous crystallization kinetics of spherical glass particles

An analytical model developed to describe the crystallization kinetics of spherical glass particles has been derived in this work. A continuous phase transition from three-dimensional (3D)-like to 1D-like crystal growth has been considered and a procedure for the quantitative evaluation of the critical time for this 3D-1D transition is proposed. This model also allows straightforward determination of the density of surface nucleation sites on glass powders using differential scanning calorimetry data obtained under different thermal conditions. © 2009 The American Ceramic Society.

Repair of bone cavities in dog's mandible filled with inorganic bovine bone and bioactive glass associated with platelet rich plasma

The aim of this study was to evaluate the effect of platelet rich plasma (PRP) associated to bovine inorganic bone (Bio-Oss®; Geistlich) or bioactive glass (Bio-Gran®; Orthovita, Implant Innovations) on bone healing. Bone cavities were prepared in both sides of the mandible of 4 adult male dogs. The cavities were divided into 4 groups according to the filling material as follows: control, PRP, PRP/Bio-Oss, PRP/Bio-Gran. The animals were sacrificed after 120 days and histological and histomorphometrical analysis was performed. The control group showed 80.6% of bone formation in the longitudinal sections at 6 mm depth and 83.7% at 13 mm depth. The transverse sections displayed 74.2% at both 6 and 13 mm depths. The PRP group showed 21.1% of bone formation in the longitudinal sections at 6 mm depth, and 23.1% at 13 mm depth. The transverse sections presented 28.98% of bone formation at 6 mm depth and 41.2% at 13 mm depth. The PRP/Bio-Gran group showed 25.1% of bone formation in the longitudinal sections at 6 mm depth and 30.4% at 13 mm depth. In the transverse sections, the bone formation was 43.0% at 6 mm depth and 39.7% at 13 mm depth. The PRP/Bio-Oss group showed 35.5% of bone formation in the longitudinal sections at 6 mm depth and 42% at 13 mm depth. In the transversal sections, the bone formation was 26.8% and 31.2% at the depths of 6 and 13 mm, respectively. PRP alone or associated with bovine inorganic bone or bioglass had no significant effect in bone healing.

Cellular decomposition of quaternionic spherical space forms

We obtain an explicit cellular decomposition of the quaternionic spherical space forms, manifolds of positive constant curvature that are factors of an odd sphere by a free orthogonal action of a generalized quaternionic group. The cellular structure gives and explicit description of the associated cellular chain complex of modules over the integral group ring of the fundamental group. As an application we compute the Whitehead torsion of these spaces for any representation of the fundamental group. © 2012 Springer Science+Business Media B.V.