Teflon Matrix Research Articles

INFLUÊNCIA DE DIFERENTES UNIDADES POLIMERIZADORAS NA RESISTÊNCIA DE UNIÃO AO CISALHAMENTO ENTRE DIFERENTES METAIS E UMA RESINA INDIRETA

Purpose: To evaluate the effect of different polymerization units on the shear bond strength between different metals and a laboratorial resin. Method: Sixty metallic cylinders were obtained (5mm x 4mm), thirty in commercially pure titanium (CpTi) and thirty in gold-palladium alloy (Au-Pd), which were sandblasted (Al2O3 110µm, 20s, 2,9 bar) before the resin application. Two layers of opaque (Sinfony Opaque) were applied with a brush and with the assistance of the teflon matrix, the esthetic veneering resin was applied on the metallic cylinders. The opaque and veneering resin were polymerized at different polymerized, according to experimental groups: GrA1 – CpTi + Visio Beta (3M ESPE/EUA); GrA2 – CpTi + Powerlux (EDG, Brazil); GrA3 – CpTi + Strobolux (EDG, Brasil); GrB1 – Au-Pd + Visio Beta; GrB2 – Au-Pd + Powerlux; GrB3 – Au-Pd + Strobolux. The specimens were submitted to shear test in a universal testing machine (model DL/1000-EMIC) with a 500kg load cell (0,5 mm/min). The data (MPa) were submitted to the analysis of variance (ANOVA) and tukey’s test (5%). Results: The means and standard deviations obtained were (MPa): GrA1: 6.1±1.9; GrA2: 5.6±1.4; GrA3: 5.5±2.5; GrB1: 9.4±2.5; GrB2: 7.4±2; GrB3: 8.2±3.1. Only the principal factor “metal” (p=0.0001 0.05) did not influenced the bond strength between resin and metal (VisioBeta= 7,8 MPa; Powerlux=6,6 MPa; Strobolux=6,8 MPa). Conclusion: The Au-Pd alloys promote higher bond strength to sinfony indirect resin compared to Ticp, regardless the polymerized unit used. Descriptors: shear bond strength; commercially pure titanium; Au-Pd alloy; indirect resin; polymerized unit.

In vitro comparison of the radiopacity of cavity lining materials with human dental structures

Aim:To compare the optical densities (OD) of calcium hydroxide (CH) and glass ionomer cement with the same thicknesses of the dental structures.Materials and Methods:Eighteen specimens of each material, with thicknesses of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm were made in a Teflon matrix. To compare the radiopacity of the materials with the dental structures, dental cuts of the first molars, increasing in thickness from 0.5 to 3.0 mm, were obtained. To standardize the radiographs, a transparent acrylic matrix (Standardizing Device) was developed and used. Thirty radiographs were taken, five for each tested material.Results:Statistical analysis (Two-way ANOVA - Bonferroni, P < 0.05) demonstrated that when the materials were compared, there was statistically significant difference between the ODs, only for the thickness of 1.0 mm (P < 0.05).Conclusion:The thickness of the material contributed to its radiopacity, and these materials had to be used in a thickness between 1.5 and 2.0 mm.

Flexural Strength of Glass‐Infiltrated Zirconia/Alumina‐Based Ceramics and Feldspathic Veneering Porcelains

To compare the flexural strength of two glass-infiltrated high-strength ceramics and two veneering glass-ceramics. Four ceramic materials were tested: two glass-infiltrated high-strength ceramics used as framework in metal-free restorations [In-Ceram Zirconia IZ (Gr1) and In-Ceram Alumina IA (Gr2)], and two glass-ceramics used as veneering material in metal-free restorations [Vita VM7 (Gr3) and Vitadur-alpha (Gr4)]. Bar specimens (25 x 5 x 2 mm3) made from core ceramics, alumina, and zirconia/alumina composites were prepared and applied to a silicone mold, which rested on a base from a gypsum die material. The IZ and IA specimens were partially sintered in an In-Ceram furnace according to the firing cycle of each material, and then were infiltrated with a low-viscosity glass to yield bar specimens of high density and strength. The Vita VM7 and Vitadur-alpha specimens were made from veneering materials, by vibration of slurry porcelain powder and condensation into a two-part brass Teflon matrix (25 x 5 x 2 mm3). Excess water was removed with absorbent paper. The veneering ceramic specimens were then removed from the matrix and were fired as recommended by the manufacturer. Another ceramic application and sintering were performed to compensate the contraction of the feldspar ceramic. The bar specimens were then tested in a three-point bending test. The core materials (Gr1: 436.1 +/- 54.8; Gr2: 419.4 +/- 83.8) presented significantly higher flexural strength (MPa) than the veneer ceramics (Gr3: 63.5 +/- 9.9; Gr4: 57.8 +/- 12.7). In-Ceram Alumina and Zirconia were similar statistically and more resistant than VM7 and Vitadur-alpha.

Controlled reduction of size of Ag nanoparticles embedded in teflon matrix by MeV ion irradiation

MeV ion irradiation of Ag-Teflon nanocomposite (NC) films, which were synthesized by co-sputtering, was studied in this work. Irradiation of these NC thin films with 100MeV Ag8+ ions at fluences from 3×1011 to 1×1012ions/cm2 resulted in the reduction of size of Ag NPs as evident by the increase in width of plasmon absorption band and red shift in plasmon absorption peak. TEM results confirmed the decrease in size of NPs by the changes evident from the particle size distribution, which emphasize the role of ion beams in nano-engineering. This article reports the possibility of reduction in size and size distribution in controlled fashion by swift heavy ion irradiation.

CME Information Neutropenia: overview and current therapies

Dental porcelain restorations are subject to biological failures related to secondary caries and periodontal disease leading to prosthesis replacement.The purpose of this in vitro study was to explore the microbiological and mechanical properties of dental porcelain incorporated with different percentages of silver vanadate (β-AgVO3) through microbiological analysis, roughness tests, and the Vickers microhardness test.IPS InLine porcelain specimens were made by using a cylindrical Teflon matrix in the dimensions of 8×2 mm. For the control group, the porcelain was manipulated according to the manufacturer's instructions. The groups incorporating the nanomaterial were prepared with 2.5%, 5%, and 10% of β-AgVO3, which was added proportionally by mass to the porcelain powder. In vitro microbiologic analysis, roughness tests, and the Vickers microhardness test were performed.Against Streptococcus mutans, the control group showed no inhibition halo (0 mm). All groups with AgVO3 showed a zone of inhibition, the highest for the group with 10% (30 mm) and then the groups with 2.5% (9 mm) and 5% (17 mm). For Vickers microhardness, no statistically significant difference (P<.05) was observed between the evaluated groups. The group with 10% of AgVO3 had the highest mean roughness and was statistically different (P<.001) from the other groups.Adding β-AgVO3 to dental porcelain demonstrated antimicrobial effectiveness at all concentrations (2.5%, 5%, and 10%), with no effect on Vickers microhardness. The 10% group had higher roughness than the other groups.

Effects of cleaning agents on bond strength to dentin

The cleaning of cavity walls aims to improve adhesive restorative procedures and longevity of restorations. This study has compared the effect of three cleaning agents--sodium bicarbonate jet (Profi II, Dabi Atlante, São Paulo, Brazil); pumice paste plus a biologic detergent (Tergestesim, Probem, São Paulo, Brazil); air water spray--on the bond strength between dentin and two different adhesive systems: Clearfil SE Bond (Kuraray, Kioto, Japan) and Scotchbond Multi-Purpose Plus (3M-ESPE, São Paulo, Brazil). Six groups (n: 10) of dental fragments obtained from young adult extracted teeth were prepared, and each one received one of the listed surface cleaning techniques. After the adhesive application, a cone-shaped test body was built with AP-X (Kuraray, Kioto, Japan) or Z100 (3M-ESPE, São Paulo, Brazil) composite resins, using a Teflon matrix. The specimens were tested for tensile bond strength after one-week storage in distilled water at 37 degrees C. Two pairs of fractured specimens of each group were randomly chosen and processed for scanning electron microscopy (SEM) analysis. ANOVA test of the bond strength values showed no statistical differences among the cleaning agents and neither between their interactions with the bonding systems. Upon SEM analysis, most surfaces showed mixed fractures of adhesive and cohesive failures in bonding resin to dentin. Based on statistical and SEM analysis, it was concluded that the cleaning agents studied did not interfere with the bond strength of the adhesive systems used to dentin.

Detonation in an aluminum-Teflon mixture

Detonation in an aluminum-fluoroplastic-4 (Teflon) mixture is studied experimentally. To increase reactivity, the initial mixture is pretreated in a mechanochemical activator. As a result, a mechanically activated composite is obtained in the form of thin aluminum layers in a Teflon matrix. The action of a shock wave on a composite sample initiates the steady detonation regime, in which the initial and final substances are in the condensed state. Depending on the percentage composition and density of the mixture, the detonation velocity varies from 700 to 1300 m/s for the speed of sound below 100 m/s in the initial composition. The steady detonation velocity changes insignificantly when sample pores are filled with helium instead of air. The results prove that it is possible in principle to reach the steady detonation regime in reactive condensed mixtures forming final reaction products in the solid state.

Comparison of chemical composition of packable resin composites by scanning electron microscopy

the purpose of this study was to compare the chemical composition of four different shades (incisal/extra-light, A2, A3 and B3) of two packable resin composites (SOLITAIRE®, and PRODIGY CONDENSABLE TM). the specimens measured 4mm in diameter and 4mm in thickness. Five specimens were made for each shade of the materials. They were light cured for 40 seconds at a power of 600mW/cm². Subsequently, the specimens were removed from the plates and ground to powder and then pressed into holes measuring 4mm in diameter in a Teflon matrix, using the plates of the same material as base and cover. Specimens were evaluated under SEM with an x-ray detector for the spectroscopic test by energy dispersing. the chemical components found in both materials were practically the same, but in different proportions. Carbon, Oxygen, Aluminum, Silica, Fluoride and Barium were found. the chemical composition of each same material varied according to each shade analyzed.

Evaluation of the shear bond strength of the union between two CoCr-alloys and a dental ceramic

Based on the importance of the integrity of the metal/ceramic interface, the purpose of this work was to evaluate the shear bond strength of the metal-ceramic union of two Co-Cr alloys (Wirobond C, Bego; Remanium 2000, Dentaurum) combined with Omega 900 ceramic (Vita Zahnfabrik). Eleven cylindrical matrixes were made for each alloy, and the metallic portion was obtained with the lost wax casting technique with standardized waxing of 4mm of height and of 4mm of diameter. The ceramic was applied according to the manufacturer's recommendations with the aid of a teflon matrix that allowed its dimension to be standardized in the same size as the metallic portion. The specimens were submitted to the shear bond test in an universal testing machine (EMIC), with the aid of a device developed for such intention, and constant speed of 0.5mm/min. The mean resistance was 48.387MPa for Wirobond C alloy, with standard deviation of 17.718, and 55.956MPa for Remanium 2000, with standard deviation of 17.198. No statistically significant difference was observed between the shear strength of the two metal-ceramic alloys.

On the aggregation process of ceramic LiSn2P3O12 particles embedded in Teflon matrix

Composites having ceramic LiSn2P3O12 particles, that are Li+ ion conductor, and Teflon, that is an insulating polymer and works as binder, have been prepared in a wide compositional range (from 8 to 74% by volume of LiSn2P3O12). Their microstructure, as followed by Scanning Electron Microscopy, has been analyzed to understand the aggregation process of the ceramic particles. For low LiSn2P3O12 contents (below 30% by volume) some particles lay isolated and some aggregated in clusters (isolated clusters) both being surrounded by Teflon. For higher LiSn2P3O12 contents the isolated clusters grow and transform into clusters that are developed along the composite bulk (extended clusters); the latter clusters accounts for the ionic conductivity, which is discussed in terms of a percolation model. The shape and size of both types of clusters are analyzed as the LiSn2P3O12 content increases. The aggregation process here described could work in other composites made from mixing and compacting particles of a ceramic and a polymer.

Statistical studies on the light output and energy resolution of small LSO single crystals with different surface treatments combined with various reflector materials

The optimization of light output and energy resolution of scintillators is of special interest for the development of high resolution and high sensitivity PET. The aim of this work is to obtain statistically reliable results concerning optimal surface treatment of scintillation crystals and the selection of reflector material. For this purpose, raw, mechanically polished and etched LSO crystals (size 2×2×10 mm 3) were combined with various reflector materials (Teflon tape, Teflon matrix, BaSO 4) and exposed to a 22Na source. In order to ensure the statistical reliability of the results, groups of 10 LSO crystals each were measured for all combinations of surface treatment and reflector material. Using no reflector material the light output increased up to 551±35% by mechanical polishing the surface compared to 100±5% for raw crystals. Etching the surface increased the light output to 441±29%. The untreated crystals had an energy resolution of 24.6±4.0%. By mechanical polishing the surface it was possible to achieve an energy resolution of 13.2±0.8%, by etching of 14.8±0.7%. In combination with BaSO 4 as reflector material the maximum increase of light output has been established to 932±57% for mechanically polished and 895±61% for etched crystals. The combination with BaSO 4 also caused the best improvement of the energy resolution up to 11.6±0.2% for mechanically polished and 12.2±0.3% for etched crystals. Relating to the light output there was no significant statistical difference between the two surface treatments in combination with BaSO 4. In contrast to this, the statistical results of the energy resolution have shown the combination of mechanical polishing and BaSO 4 as the optimum.

Experimental Dentin-Based Approaches to Tissue Regeneration in Vital Pulp Therapy

The potential direct induction of odontoblastlike cell differentiation at the surface of implanted dentin matrix has been tested in a series of capping experiments. Pieces of Teflon (control) or autogenous dentin matrix were placed in contact with the wound surface at a conventional capping situation, or at the dentinal base of the cavity at a distance from the exposed pulp periphery. Tissue responses were studied by light microscopy after periods of 2 and 4 weeks. Partial degradation of the dentin matrix implants was seen. Formation of atubular calcified matrix, occasionally followed by tubular reparative dentin, was consistently detected in association with dentinal particles. The area between the traumatized dental pulp periphery and the capping material had been occupied by a well-vascularized tissue, regardless of the capping material and postoperative time period. Traces of calcified matrix were detected along the cut dentinal walls. The present data indicate that dentin matrix is limited in its ability to directly induce odontoblastlike cell differentiation and reparative dentin formation at the surface of mechanically exposed pulp of mature teeth. Furthermore, it seems that the traumatized mature pulp maintains the ability to grow, while a calcifying potential could be expressed by this growing part of the pulp core.

Graphite-teflon composite bienzyme electrodes for the determination of cholesterol in reversed micelles. Application to food samples.

A bienzyme amperometric composite biosensor for the determination of free and total cholesterol in food samples is reported. Cholesterol oxidase and horseradish peroxidase, together with potassium ferrocyanide as a mediator, are incorporated into a graphite-70% Teflon matrix. The compatibility of this biosensor design with predominantly nonaqueous media allows the use of reversed micelles as working medium. The reversed micelles are formed with ethyl acetate as continuous phase (in which cholesterol is soluble), a 4% final concentration of 0.05 mol L(-1) phosphate buffer solution, pH 7.4, as dispersed phase, and 0.1 mol L(-1) AOT as emulsifying agent. Studies on the repeatability of the amperometric response obtained at +0.10 V, with and without regeneration of the electrode surface by polishing, on the useful lifetime of one single biosensor and on the reproducibility in the fabrication of different pellets illustrate the robustness of the biosensor design. Determination of free and total cholesterol in food samples such as butter, lard, and egg yoke was carried out, and the obtained results were advantageously compared with those provided by using a commercial Boehringer test kit.

Influence of disinfectant solutions on the tensile bond strength of a fourth generation dentin bonding agent

The purpose of the present study was to evaluate the influence of different disinfectant solutions on the tensile bond strength of a fourth generation dentin bonding agent. Forty non carious human molars were selected. Teeth were embedded in acrylic resin and ground until the exposure of a flat superficial dentin surface. Teeth were randomly divided in 4 groups and treated as follows: Group 1 - 2.5% NaOCl for 40 seconds; Group 2 - 2% chlorhexidine for 40 seconds; Group 3 - 1.23% acidulated fluoride for 4 minutes; and Group 4 - control (without disinfectant solution). Following treatments, Scotchbond Multipurpose Plus® (3M) was used according to the manufacturer’s instructions. After that, the test specimens were built with composite resin (Z100®-3M), using a standard Teflon matrix. The specimens were stored in distilled water for 24 hours at a temperature of 37ºC. The tensile strength test was performed using a Mini Instrom testing machine. The mean values obtained for each group, in MPa, were: Group 1 - 7.37 (± 2.51); Group 2 - 11.25 (± 4.65); Group 3 - 9.80 (± 3.11); and Group 4 - 10.96 (± 3.37). The results were submitted to statistical analysis using the ANOVA test, and no statistical significant differences among the groups were found. It can be concluded that the different disinfectant substances used in this research do not adversely affect dentin adhesion.

Development of a bienzymic graphite–Teflon composite electrode for the determination of hypoxanthine in fish

A bienzymic amperometric graphite–Teflon composite biosensor, in which xanthine oxidase and peroxidase, together with the mediator ferrocene, are incorporated into the electrode matrix, was developed for the determination of hypoxanthine in fish samples. These biosensors were fabricated by simple physical inclusion of the enzymes and the mediator in the bulk of the graphite–Teflon matrix. A Teflon content of 60%, a working potential of 0.00 V, a temperature of 30 ± 1 °C and a pH of 7.4 were selected as the optimum working conditions. The composite bioelectrode operated over long periods owing to the renewability of its surface by polishing. Reproducible amperometric responses were achieved with different electrodes fabricated from different composite matrices, and no significant loss of the enzyme activity was observed after more than 6 months of storage at 4 °C. A detection limit for hypoxanthine of 9.0 × 10–8 mol l–1 was obtained by amperometry in stirred solutions. An interference study of different substances which may be present in samples together with hypoxanthine demonstrated very good selectivity for the determination of this analyte. The bienzymic composite biosensor was applied to the determination of hypoxanthine in sardine muscle tissue, and the method was validated by comparing the results with those obtained by applying a recommended reference method.

Graphite−Poly(tetrafluoroethylene) Composite Enzyme Electrodes as Suitable Biosensors in Predominantly Nonaqueous Media

The performance of a graphite-poly(tetrafluoroethylene) Teflon composite amperometric ferrocyanide-mediated peroxidase electrode in a predominantly nonaqueous medium such as reversed micelles is discussed and compared with the behavior in a medium formed by acetonitrile/water. The composite electrode was constructed by purely physical entrapment of both the enzyme and the mediator into the bulk of the graphite-Teflon matrix with no need of covalent attachments. This biosensor responded rapidly to the changes in the concentration of both hydrogen peroxide and 2-butanone peroxide in reversed micelles formed with ethyl acetate, 0.1 mol L(-)(1) dioctyl sulfosuccinate as the surfactant, and a 4% phosphate buffer (pH 7.4) as the dispersed phase. The electrode showed a long-term operation due to the renewability of its surface. Moreover, reproducible responses were obtained with different electrodes fabricated from different composite matrixes. No significant loss of the enzyme activity was observed after four months of dry storage at 4 °C of the composite electrode. Limits of detection of 2.1 × 10(-)(7) and 3.5 × 10(-)(7) mol L(-)(1) were obtained for H(2)O(2) and 2-butanone peroxide, respectively. The possibility of using this biocomposite electrode in flowing systems, using the reversed micelles as the carrier, has been demonstrated. The kinetic of the enzymatic reaction was faster in a 90:10 acetonitrile/phosphate buffer medium than in reversed micelles, which can be attributed to the higher water content present in the former medium. A similar stability of the biosensor and a slightly better sensitivity for peroxides was observed in the acetonitrile/water mixture when compared with reversed micelles. Finally, the electrode also performed well in the flow injection mode.

The Influence of Binders on Interfacial Failure in Sapphire Fiber-reinforced NiAl Composites

The influence of organic binders on fiber/matrix bonding during the powder metallurgy fabrication of sapphire fiber-reinforced NiAl matrix composites (sapphire/NiAl) was investigated. One composite panel was fabricated using a poly(methyl methacrylate) (PMMA) fiber binder and a teflon matrix powder binder; another panel was fabricated by binderless powder metallurgy consolidation. The effect of the binders on fiber/matrix bonding was evaluated by fiber push-out testing from room temperature to 900 °C. Examination of mating fiber and matrix-trough fracture surfaces by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) revealed differences in interfacial morphology and chemistry, depending on the use of binders in fabrication. The primary difference between the two composites was the much higher concentration of carbon at the fiber/matrix interface in sapphire/NiAl fabricated with binders. This carbon residue from binder burnout prevented clean contact between the sapphire fiber and NiAl matrix surfaces, resulting in a weak, thermomechanically clamped fiber/matrix interface, in contrast to the stronger, less temperature dependent, interfacial bonding observed without binders.

Beta particle attenuation characteristics of CaSO4.

The beta particle mass attenuation coefficient for CaSO4 in a Teflon matrix has been estimated by two methods: an experiment using collimated sources and a collimated gas flow proportional counter and simulations using the EGS4 Monte Carlo code. The attenuation coefficient has been cast in the general form of mu/rho = aE(-b), where E is the maximum beta particle energy and a and b are fitting parameters. The a and b parameters are given as a function of the atomic number of the material.

Mini features

DuPont in Europe has introduced chemical‐ and creep‐resistant machined finished parts and stock shapes in “Zymaxx”, a high temperature Teflon matrix with a specially treated high aspect ratio carbon fibre reinforcement.

Considerations on the calibration of small thermoluminescent dosimeters used for measurement of beta particle absorbed doses in liquid environments.

An investigation has been carried out on the factors which affect the absolute calibration of thermoluminescent dosimeters (TLDs) used in beta particle absorbed dose evaluations. Four effects on light output (LO) were considered: decay of detector sensitivity with time, finite TLD volume, dose linearity, and energy dependence. Most important of these was the decay of LO with time in culture medium, muscle tissue, and gels. This permanent loss of sensitivity was as large as an order of magnitude over a 21-day interval for the nominally 20-microns-thick disc-shaped CaSO4(Dy) TLDs in gel. Associated leaching of the dosimeter crystals out of the Teflon matrix was observed using scanning electron microscopy. Large channels leading from the outside environment into the TLDs were identified using SEM images. A possibility of batch dependence of fading was indicated. The second most important effect was the apparent reduction of light output due to finite size and increased specific gravity of the dosimeter (volume effect). We estimated this term by calculations as 10% in standard "mini" rods for beta particles from 90Y, but nearly a factor of 3 for 131I beta particles in the same geometry. No significant nonlinearity of the log (light output) with log (absorbed dose) over the range 0.05-20.00 Gy was discovered. Energy dependence of the LO was found to be not detectable, within measurement errors, over the range of 0.60-6.0 MeV mean energy electrons. With careful understanding of these effects, calibration via gel phantom would appear to be an acceptable strategy for mini TLDs used in beta absorbed dose evaluations in media.(ABSTRACT TRUNCATED AT 250 WORDS)