Maxillary canine-first premolar transposition - Restoring normal tooth order with segmented mechanics

Tooth transpositions present at a relatively low incidence in the world population and primarily affect maxillary canines and premolars. Treatment of this disturbance should take into account aspects such as facial pattern, age, malocclusion, tooth-size discrepancy, stage of eruption, and magnitude of the transposition. Mechanics for correction should be entirely individualized, reducing the risks and adverse effects. Practitioners often select simpler options, indicating extraction of permanent teeth, which is an irreversible procedure that may bring about damages to the patient. This study presents a case report and treatment of unilateral transposition of maxillary canine and premolar with repositioning of affected teeth to their respective normal positions.

Analytical procedure for total mercury determination in fishes and shrimps by chronopotentiometric stripping analysis at gold film electrodes after microwave digestion

A method for the total mercury determination in fish and shrimps employing chronopotentiometric stripping analysis on gold film electrodes is described. Fish and shrimp tissues were digested using a microwave oven equipped with closed vessels. We developed a microwave heating program which decomposed all the samples employing diluted nitric acid and hydrogen peroxide. The proposed method was validated by analyzing a certified reference material and then applied for different fish species from fresh water and seawater acquired in local markets of São Paulo city, Brazil. The Brazilian legislation establishes 0.5 and 1 mg per kilogram of fish as upper limit of mercury for omnivorous and predator species, respectively. Except for blue shark tissues, the mercury content was situated below 0.5 mu g g(-1) for all the analyzed samples. The detection limit of the proposed method was calculated as 5 ng g(-1) of sample utilizing 5 minutes of electrodeposition (+300 mV vs. Ag/AgCl) on the gold electrode. (c) 2006 Elsevier Ltd. All rights reserved.

Epitaxial growth of LiNbO3 thin films in a microwave oven

Oriented LiNbO3 thin films were prepared using a polymeric precursor solution deposited on (0001) sapphire substrate by spin coating and crystallized in a microwave oven. Crystallization of the films was carried out in a domestic microwave oven. The influence of this type of heat treatment on the film orientation was analyzed by X-ray diffraction and electron channeling patterns, which revealed epitaxial growth of films crystallized at 550 and 650 degreesC for 10 min. A microstructural study indicated that the films treated at temperatures below 600 degreesC were homogeneous and dense, and the optical properties confirmed the good quality of these films. (C) 2003 Elsevier B.V. B.V. All rights reserved.

The effect of polymerization cycles on porosity of microwave-processed denture base resin

Statement of problem. Although most of the physical properties of denture base resin polymerized by microwave energy have been shown to be similar to resins polymerized by the conventional heat polymerization method, the presence of porosity is a problem.Purpose. This study evaluated the effect of different microwave polymerization cycles on the porosity of a denture base resin designed for microwave polymerization.Material and methods. Thirty-two rectangular resin specimens (65 X 40 X 5 mm) were divided into 3 experimental groups (A, B, and C; Onda-Cryl, microwave-polymerized resin) and I control group (T; Classico, heat-polymerized resin), according to the following polymerization cycles: (A) 500 W for 3 minutes, (B) 90 W for 13 minutes + 500 W for 90 seconds, (C) 320 W for 3 minutes + 0 W for 4 minutes + 720 W for 3 minutes, and (T) 74degreesC for 9 hours. Porosity was calculated by measurement of the specimen volume before and after its immersion in water. Data were analyzed using 1-way analysis of variance (alpha = .05).Results. The mean values and SDs of the percent mean porosity were: A = 1.05% +/- 0.28%, B = 0.91% +/- 0.15%, C = 0.88% +/- 0.23%, T = 0.93% +/- 0.23%. No significant differences were found in mean porosity among the groups evaluated.Conclusion. Within the limitations of this study, a denture base resin specifically designed for microwave Polymerization tested was not affected by different polymerization cycles. Porosity was similar to the conventional heat-polymerized denture base resin tested.

Spectrophotometric determination of formaldehyde with chromotropic acid in phosphoric acid medium assisted by microwave oven

In the present study. a spectrophotometric method for the determination of formaldehyde by using chromotropic acid was devised. in which the use of potentially hazardous and corrosive concentrated sulfuric acid was eliminated and advantageously C replaced by a mixture of H, concentrated H3PO4 and H2O2. The reaction between formaldehyde and chromotropic acid (CA) in a cone phosphoric acid medium was accelerate by irradiating the mixture with microwave energy for 35 s (1100 W), producing a violetred compound (lambda(max)=570 nm). Beer's Law is obeyed in a concentration range of 0.8-4.8 mg 1(-1) of formaldehyde with a good correlation coefficient (r = 0.9968). The proposed method was applied in the analysis of formaldehyde in commercial disinfectants. Recoveries were within 98.0-100.4%, with standard deviations ranging from 0.03 to 0.13%. (C) 2003 Elsevier B.V All rights reserved.

Ferroelectric and piezoelectric properties of bismuth titanate thin films grown on different bottom electrodes by soft chemical solution and microwave annealing

Bismuth titanate (Bi4Ti3O12, BIT) films were evaluated for use as lead-free piezoelectric thin films in micro-electromechanical systems. The films were grown by the polymeric precursor method on LaNiO3/SiO2/Si (1 0 0) (LNO), RuO2/SiO2/Si (1 0 0) (RuO2) and Pt/Ti/SiO2/Si (1 0 0) (Pt) bottom electrodes in a microwave furnace at 700 degrees C for 10 min. The domain structure was investigated by piezoresponse force microscopy (PFM). Although the converse piezoelectric coefficient, d(33), regardless of bottom electrode is around (similar to 40 pm/V), those over RuO2 and LNO exhibit better ferroelectric properties, higher remanent polarization (15 and 10 mu C/cm(2)), lower drive voltages (2.6 and 1.3 V) and are fatigue-free. The experimental results demonstrated that the combination of the polymeric precursor method assisted with a microwave furnace is a promising technique to obtain films with good qualities for applications in ferroelectric and piezoelectric devices. (c) 2006 Elsevier Ltd. All rights reserved.

Residual monomer of reline acrylic resins - Effect of water-bath and microwave post-polymerization treatments

Objectives. This study compared the residual monomer (RM) in four hard chair-side reline resins (Duraliner II-D, Kooliner-K, Tokuso Rebase Fast-TRF and Ufi Gel hard-UGH) and one heat-polymerized denture base resin (Lucitone 550-L), which was processed using two polymerization cycles (short-LS and long-LL). It was also investigated the effect of two after polymerization treatments on this RM content.Methods. Specimens (n = 18) of each material were produced following the manufacturers' instructions and then divided into three groups. Group I specimens were left untreated (GI-control). Specimens of group II (GII) were given post-polymerization treatment by microwave irradiation. In group III (GIII), specimens were submitted to immersion in water at 55 degrees C (reline resins-10 min; denture base resin L-60min). The RM was analyzed using high performance liquid chromatography (HPLC) and expressed as a percentage of RM. Data were analyzed by two-way ANOVA followed by Tukey's test (alpha = 0.05).Results. Comparing control specimens, statistical differences were found among all materials (p < 0.05), and the results can be arranged as K (1.52%) > D (0.85%) > UGH (0.45%) > LL (0.24%) > TRF (0.14%) > LS (0.08%). Immersion in hot water (GIII) promoted a significant (p < 0.05) reduction in the RM for all materials evaluated compared to control (GI), with the exception of LL specimens. Materials K, UGH and TRF exhibited significantly (p < 0.05) lower values of RM after microwave irradiation (GII) than in the control specimens.Significance. The reduction in RM promoted by water-bath and microwave post-polymerization treatments could improve the mechanical properties and biocompatibility of the relining and denture base materials. (c) 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Microwave synthesis of YAG : Eu by sol-gel methodology

Yttrium-aluminum oxides are interesting compounds and they have been extensively used as host for lasers and phosphors, due to their stable physical and chemical properties. The fabrication of yttrium-aluminum garnet (YAG) has been investigated thoroughly. Single-crystal YAG is expensive and to produce it a new way has been investigated. This process consists of modifying the methodology of reagents mixture and the process of heating them. The microwave irradiation is used to heat-treat the oxide mixture. The traditional synthesis of YAG powders occurs through the reaction of aluminum and yttrium powders at high temperatures. With this work we investigated the preparation of YAG by non-hydrolytic sol-gel route as an alternative methodology to obtain yttrium-aluminum matrix from inorganic precursors (yttrium and aluminum chloride). The preparation of the gel was carried out in an oven-dried glassware. The AlCl3, YCl3 and ethanol were reacted in reflux under argon atmosphere. Europium III chloride was added as a structural probe. The powder was dried and heat-treated in modified microwaves. The samples were pre-treated at 50 and 800 C during I h and then heated in microwaves for 30 s, 2 and 4 min. The formation process and structure of the powders were studied by means of X-ray diffraction (XRD), photoluminescence (PL) and transmission electronic microscopy (TEM). XRD presents only picks corresponding to the YAG phase and confirmed by TEM. PL date showed that the YAG phase was formed in 2 min with the samples pre-treated at 50 C. For the samples pretreated at 800 degrees C, the YAG phase appears in 30s. The excitation spectra present a maximum of 394 nm corresponding to the L-5(6) level and emission spectra of Eu III ion present bands characteristic transitions arising from the D-5(0) -> F-7(J) (J= 1, 2, 3, 4) monifolds excited at their maximum. The magnetic dipole D-5(0) -> F-7(1) transition presents more intensity than the electric dipole D-5(0) -> F-7(2) transition. This methodology showed efficiency in obtaining YAG phase. (c) 2006 Elsevier B.V. All rights reserved.

Localized mechanics of dentin self-etching adhesive system

The bond strength of composite resins (CRs) to dentin is influenced by the interfacial microstructure of the hybrid layer (HL) and the resin tags (TAG). The contemporary self-etching primer adhesive systems overcame the inconvenient of the etch-and-rinse protocol. Studies, however, have demonstrated that HL thickness and TAG length vary according to the wetting time and additional use of acid-etching prior to self-etching primers. This study investigated the localized stress distribution in the HL and the dentin/adhesive interface. Two HL thicknesses (3 or 6 mu m), two TAG lengths (13 or 17 mu m) and two loading conditions (perpendicular and oblique-25 degrees) were investigated by the finite element (FE) analysis. Five two-dimensional FE models (M) of a dentin specimen restored with CR (38 x 64 mu m) were constructed: M1 - no HL and no TAG; M2 - 3 mu m of HL and 13 mu m of TAG; M3 - 3 mu m of HL and 17 mu m of TAG; M4 - 6 mu m of HL and 13 mu m of TAG; and M5 - 6 mu m of HL and 17 mu m of TAG. Two distributed loadings (L) (20N) were applied on CR surface: L1 - perpendicular, and L2 - oblique (25 degrees). Fixed interfacial conditions were assigned on the border of the dentin specimen. Ansys 10.0 (Ansys (R), Houston, PA, USA) software was used to calculate the stress fields. The peak of von Mises (sigma(vM)) and maximum principal stress (sigma(max)) was higher in L2 than in L1. Microstructures (HL and TAG) had no effect on local stresses for L1. Decreasing HL decreased sigma(vM) and sigma(max) in all structures for L2, but the TAG length had influence only on the peributular dentin. The thickness of HL had more influence on the sigma(vM) and sigma(max) than TAG length. The peritubular dentin and its adjacent structures showed the highest sigma(vM) and sigma(max), mainly in the oblique loading.

Renormalization in non-relativistic quantum mechanics

The importance and usefulness of renormalization are emphasized in non-relativistic quantum mechanics. The momentum space treatment of both two-body bound state and scattering problems involving some potentials singular at the origin exhibits ultraviolet divergence. The use of renormalization techniques in these problems leads to finite converged results for both the exact and perturbative solutions. The renormalization procedure is carried out for the quantum two-body problem in different partial waves for a minimal potential possessing only the threshold behaviour and no form factors. The renormalized perturbative and exact solutions for this problem are found to be consistent with each other. The useful role of the renormalization group equations for this problem is also pointed out.

Effect of the heat flux direction on electrical properties of SrBi2Nb2O9 thin films crystallized using a microwave oven

Ferroelectric SrBi2Nb2O9 (SBN) thin films were prepared by the polymeric precursors method and deposited by spin coating onto Pt/Ti/SiO2/Si substrate and crystallized using a domestic microwave oven. It was studied the influence of the heat flux direction and the duration of the thermal treatment on the films crystallization. An element with high dielectric loss, a SiC susceptor, was used to absorb the microwave energy and transfers the heat to the film. Influence of the susceptor position to the sample crystallization was verified, the susceptor was, placed or below the substrate or above the film. The SBN perovskite phase was observed after a thermal treatment at 700 degreesC for 10 min when the susceptor was placed below the substrate and for 30 min when the susceptor was placed above the film. Electrical measurements revealed that the film crystallized at 700 degreesC for 10 min, with the susceptor placed below the film, presented dielectric constant, dielectric loss, remanent polarization and coercive field of, 67, 0.011, 4.2 muC/cm(2) and 27.5 kV/cm, respectively. When the films were crystallized at 700 degreesC for 30 min, with the susceptor placed above the film, the dielectric constant was 115 and the dissipation factor was around of 0.033, remanent polarization and coercive field were 10.8 muC/cm(2) and 170 kV/cm, respectively. (C) 2003 Elsevier B.V. All rights reserved.

Generalized point interactions in one-dimensional quantum mechanics

There is a four-parameter family of point interactions in one-dimensional quantum mechanics. They represent all possible self-adjoint extensions of the kinetic energy operator. If time-reversal invariance is imposed, the number of parameters is reduced to three. One of these point interactions is the familiar delta function potential but the other generalized ones do not seem to be widely known. We present a pedestrian approach to this subject and comment on a recent controversy in the literature concerning the so-called delta' interaction. We emphasize that there is little resemblance between the delta' interaction and what its name suggests.