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  • 1
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Kinetic analysis of thermogravi metric data in visible-light-cured composite restoratives has been carried out and a comparison was made with that for a conventional chemically-cured composite. The results reveal that the thermal decomposition of polymers as the base resin in the composites rnay be governed by a single process, and the value of activation energy is different in decomposing the base resins thermally. The different values suggest that the kinds of base resins and the catalysts may have an effect on the thermal decomposition.
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  • 2
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The effect of filler content and size to property of composite resin using high purity spherical silica particles on microwave curing was examined by mechanical means and electron microscope observation to develop microwave-curing composite resin inlay. Increasing filler content in three kinds of filler particles (0.45, 0.96 and 1.46 μm) resulted in increasing compressive strength, diametral tensile strength and knoop hardness and indicated the highest values at the operative mixing limit. The effect of particle size was that the mechanical property of the 0.96 μm filled resin was highest, followed by 1.46 μm and 0.45 μm on the same filler content. The 0.96 μm filled resin had about the same knoop hardness on both surfaces of the cured sample, which means that uniform polymerization occurred in the cured sample. With electron microscope observation, the bubbles of about 1.0 μm and the cracks between the fillers and the matrix were observed in each cured resin. This is caused by the excessive absorption of microwave energy in fillers and surface treatment materials of fillers. Therefore, improvement of the composition of filler and surface treatment material of filler are needed, which makes it harder to absorb the microwave energy. ©©1999©Kluwer Academic Publishers
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  • 3
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: This experiment was designed to study the internal colour change of five experimental visible light-cured (VLC) resins and to deduce the relationship between staining and the physicochemical properties of the resins and a glass. The staining of the materials was measured colorimetrically, with immersion in two types of staining solution (Oil Orange or Food Red 3) for 70 days at 37°C. The water sorption, contact angle and zeta-potential of these samples were also measured. With the Oil Orange dye a positive relationship was observed only between staining and the contact angles, whereas with Food Red 3 dye a positive relationship was observed between staining and the zeta-potential and between staining and the water sorption. The results could allow a comparison of the relative contributions to staining made by physicochemical forces for the samples tested.
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  • 4
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: New ceramic/resin composites were prepared by filling the intercrystal spaces of a porous-CaO·SiO2-based machinable ceramic with [methyl methacrylate (MMA) + triethylene glycol dimethacrylate (TEGDMA) + Bis-phenol A glycidyl dimethacrylate (Bis-GMA)] copolymers. The composites exhibited a hardness, smaller and analogous to that of bovine enamel. Weight-load cutting tests were performed on the composites and bovine enamel, employing diamond points driven by an air-turbine handpiece. While the applied load was increased stepwise, we measured the rotational cutting speed and the cutting volume. With the addition of the applied load, the rotational cutting speed decreased and the cutting volume increased. With incrementing applied load, the degrees of the decrease in the rotational cutting speed and the increase in the cutting volume for bovine enamel were well simulated by those for the composites. It was therefore speculated that the porous-ceramic/resin composites are suitable for typodont teeth in the dental preclinical cutting exercise, and that another potential use of the composites might be in the production of future machined dental prostheses.
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  • 5
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract Urethane monomer/diluent monomer mixtures were used in dental composite resin veneering materials filled with various ratios of powder (filler)/liquid (comonomer), P/L. Hardness values of unfilled resins containing benzoyl peroxide only (BP0; 0.5 wt%), and filled resins (included trimethylol propane trimethacrylate (TMPT) composite filler) were tested. Significant increases in hardness were obtained with the use of TMPT composite filler in the resins. Also, their modulus values measured by bend test showed an increasing trend, compared to a commercial composite resin veneering material (a control sample; CONT) with a lower filler content (50 wt%). The DME–DPMDC/HPDM comonomer (dimethacryloxyethyl diphenylmethane-4,4′-dicarbamate/hydroxypropyl dimethacrylate), which showed a smaller fraction of surface porosity, gave greater mechanical strength values at P/L ratios of 0.55 (17.8 wt% filler content) to 1.20 (27.3 wt%) than a CONT resin. The coefficient of thermal expansion was smaller in urethane-based filling materials than a CONT resin. Also, greater activation energy of thermal decomposition was observed in the resin samples with P/L ratio 0.75 to 1.20 than in a CONT resin. Thermally-induced decomposition occurred with smaller weight loss in the experimental filled resins than in a CONT resin.
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  • 6
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 8
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: This study was designed to evaluate the bacterial adhesion to five types of experimental composite-based resins and a commercial composite resin used as a control. Physicochemical surface characteristics of composite resins with and without an artificial saliva coating were measured. The relationship between the numbers of adhering cells (Streptococcus sanguis, S. mutans and S. sobrinus) and surface characteristics was analysed. The values of contact angles and the number of adhering cells were small with saliva coating. S. sanguis ATCC 10557 showed a positive correlation (r=0.835, p〈0.05) with the contact angles of uncoated resins, whereas no relationship was observed for saliva-coated resins. With S. mutans Ingbritt the cell numbers adhering to resins correlated strongly (p〈0.01) with the values of zeta potential of resins for either saliva coated or uncoated. Electrical repulsion forces had a strong contribution to adherence of cells such as S. mutans and S. sobrinus which show a high absolute zeta potential.
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  • 9
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract This study was to examine water uptake, contact angle and colour change vector in relation to the staining on the optically smooth surface in five experimental visible light-cured (VLC) bis-GMA-based resins. They were formulated from bis-GMA-based resins including 25 to 45 wt% TEGDMA which were accelerated by CQ/DMAEMA/BHT = 0.5/2/0.05 (wt%) to bis-GMA/TEGDMA resin matrix. Of the set resins including more than 25 wt% of TEGDMA, the resins including 30 to 45 wt% had less than 1.0% as bis-GMA residual monomer. Water uptake and solubility in bis-GMA-based resins including 35 wt% TEGDMA were the minimum of the resins tested. Contact angle decreased with increasing time over 70 days, from 67 to 62 degrees. Using the hydrophilic staining solution (food red 3), the values of colour change vector were 6 to 9 after immersing them for 70 days at 37 °C, whereas hydrophobic oil orange staining test had a range of 12 to 19. The change of water uptake with time of immersion correlated with that of the colour change vector. With the accelerated test, the minimum value was 4.55 in 65/35 (bis-GMA/TEGDMA) resin. Of the bis-GMA-based resins (25 to 45 wt% fraction of TEGDMA) the minimum value of water uptake and contact angle were obtained.
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  • 10
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: We examined the curing behaviour by visible-light (VL) and by heat of three commercial VLC inlay composite resins and three commercial VLC direct-filling composite resins by isothermal differential scanning calorimetry (DSC) thermal analysis and DTA thermal analysis, respectively. It became evident that heat of curing with VL irradiation and activation energy for photo-polymerization differed among the composite specimens. The activation energies for VL curing of inlay composites tended to slightly exceed those of direct-filling composites. It also became clear that the activation energy for heat curing of one direct-filling composite was considerably larger than those of the other five composites. There was, however, no systematic difference in the activation energies for heat curing between inlay and direct-filling composites.
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