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  • 2000-2004  (10)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 31 (2004), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: summary  The purpose of this study was to evaluate the polymerization shrinkage of three orthodontic adhesive resins when polymerized with a high-energy plasma arc light (1340 mW cm−2) and a conventional halogen light (500 mW cm−2), and to correlate the polymerization shrinkage with the degree of conversion. To equalize the total light energy delivered to the adhesive resin, irradiation time was varied between 3 or 6 s for a plasma arc-curing unit, and 8 or 16 s for a halogen light-curing unit. The polymerization shrinkage of adhesive resins during the light-curing process was measured using a computer-controlled mercury dilatometer and the degree of conversion was measured using Fourier transform infrared spectroscopy. A plasma arccuring unit produced significantly lower polymerization shrinkage than a halogen light-curing unit when the equivalent total light energy was irradiated to the orthodontic adhesive resins (P 〈 0·05). The magnitude of polymerization shrinkage was significantly different depending on the kind of adhesive resins (P 〈 0·05), but there was no significant correlation between the filler fraction and the polymerization shrinkage (r2 = 0·039). There was strong correlation (r2 = 0·787) between the polymerization shrinkage and the degree of conversion with a halogen light-curing unit, but poor correlation (r2 = 0·377) was observed with a plasma arc-curing unit.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 31 (2004), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: summary  The purpose of this study was to evaluate the effect of the various light curing units (plasma arc, halogen and light-emitting diodes) and irradiation methods (one-step, two-step and pulse) using different light energy densities on the leachability of unreacted monomers (Bis-GMA and UDMA) and the surface hardness of a composite resin (Z250, 3M). Leachability of the specimens immersed for 7 days in ethanol was analysed by HPLC. Vicker's hardness number (VHN) was measured immediately after curing (IC) and after immersion in ethanol for 7 days. Various irradiation methods with three curing units resulted in differences in the amount of leached monomers and VHN of IC when light energy density was lower than 17·0 J cm−2 (P = 0·05). However, regardless of curing units and irradiation methods, these results were not different when the time or light energy density increased. When similar light energy density was irradiated (15·6–17·7 J cm−2), the efficiency of irradiation methods was different by the following order: one-step ≥ two-step 〉 pulse. These results suggest that the amount of leached monomers and VHN were influenced by forming polymer structure in activation and initiation stages of polymerization process with different light source energies and curing times.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 30 (2003), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: summary  The objective of this study was to compare the mechanical properties of calcium phosphate cements (CPC) for possible dental applications with varied liquid and powder compositions under the same testing condition. Cements studied in this experiment were divided into two groups of CPC not containing polymer and polymeric CPC (PCPC). Cement powder was formed by combining equimolar amounts of dicalcium phosphate anhydrous and tetracalcium phosphate, or acrylic resin polymer powder mixture. The CPC specimens for the compressive strength (CS) and diametral tensile strength (DTS) measurements were prepared by mixing powder and liquid for 30 s with a powder/liquid ratio of 3:1, and subsequently packing the paste into a brass mould. The specimens were kept at 37 °C and 100% relative humidity for 24 h before measurements were conducted on a Universal Testing Machine with a cross-head speed of 1 mm min–1. The CS of CPC was 0ḃ14–10ḃ29 MPa and that of PCPC was 0ḃ26–117ḃ58 MPa. The DTS of CPC was 0ḃ10–4ḃ56 MPa and that of PCPC was 0ḃ07–22ḃ54 MPa. The CS and DTS were very diverse depending on the composition of powder and liquid. Some compositions showed higher values than commercial liners. Thus compositions of 2% carboxymethyl cellulose + 35% citric acid in phosphate buffered saline (PBS), 20% gelatin in PBS, 2% sodium alginate in PBS, 20–40% aqueous acrylic-maleic copolymer solution, and some of the HPMC and PMVE-Ma solutions exhibited promising formulae for dentine regenerating materials. Acrylic resin-PCPC group showed generally higher CS and DTS values. Based on this study, further studies on the reaction with odontoblast and resultant dentine regeneration should be performed using promising compositions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 31 (2004), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: summary  This study determined the influence of optical properties of constituent layers on the colour of double-layer aesthetic filling materials. Multiple regression equations for the Commission Internationale de I'Eclairage (CIE) L*, a* and b* of layered materials were calculated from the optical values of the covering and underlying layers. Specimens (10 mm diameter, 1 mm thickness) of two light-cured resin composites and one compomer of seven to 11 shades were used. CIE L*, a* and b* values of each specimen were measured with a colour spectrophotometer backed by a standard white background. The scattering coefficient (S), absorption coefficient (K), contrast ratio (C) and translucency parameter (T) were calculated. Double-layered specimens were formed in optical contact by joining two different shades from the same material, or resin composite as covering with a compomer underlying layer. Each of the L*, a* and b* of layered material was used as a dependent variable, and 14 optical values of underlying and covering layers were used as independent variables in forward regression analysis (P = 0·01). CIE L* after layering had a positive correlation with S of covering layer (correlation coefficient; β = 0·79–0·91, P 〈 0·01) and a correlation with L* of underlying layer (β = 0·14–0·16). CIE a* after layering had a correlation with a* of covering layer (β = 0·83–0·94) and a correlation with a* of underlying layer (β = 0·30–0·56). CIE b* after layering had a correlation with b* of covering layer (β = 0·77–0·90) and a correlation with T of covering layer (β = 0·40–0·59). The layered colour of these materials can be predicted by the derived regression equations within the limitations of this study. CIE L*, a* and b* values of double-layer material are mainly influenced by S, CIE a* and b* of covering layer, respectively.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 31 (2004), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: summary  The objectives of this study were to determine the influence of thermocycling on the changes of elastic modulus (EM) and colour, and to evaluate cytotoxicity after repeated elution of short-term-use soft liners. Three short-term-use soft liners [soft acrylic-based Coe Comfort (CCM), Coe Soft (CST) and Soft Liner (SFL)], and long-term-use silicone-based Tokuso Soft Liner (TSL) acting as a control were studied. EM was measured at baseline and after thermocycling at 5–55 °C for 500, 1000, 1500 and 2000 cycles. For the colour measurement, specimens in discs 20 mm in diameter and 1 mm in thickness were prepared, attached to a denture base resin plate, and then thermocycled as above. Colour change (ΔE*) was measured according to the Commission Internationale de l'Eclairage (CIE) L*, a*, and b* scale on a spectrophotometer. For the cytotoxicity evaluation, specimens were eluted for 24 h in culture media repeatedly up to four times, and MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) was performed. EM of CCM and CST increased up to 1500 and 1000 cycles of thermocycling respectively. EM of SFL gradually increased up to 2000 cycles, and that of TSL increased after 500 cycles and did not change after then. ΔE* of soft liners after 2000 cycles except CCM were 3·68–8·65. EM increased up to 1000–1500 cycles, and perceivable colour change was observed after 2000 cycles in most materials. Therefore, short-term-use soft liners should be used within a limited time, although the cytotoxicity decreased after repeated elution.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 29 (2002), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: summary  The purpose of this study was to determine the effectiveness of polymerization in the newly introduced blue light emitting diode (LED) (Experimental, SNU, Korea), and plasma arc curing (PAC) (Apollo 95E, Elite, DMD, USA) compared with conventional halogen lamp (Spectrum 800, Dentsply, USA). Various irradiation time with fixed intensity of light-curing units (LCUs) were irradiated to produce the same total light energy. The degree of double bond conversion (DC) of three resin composite (shade A3) was measured with a Fourier-transform infrared (FT-IR) spectrophotometer at various depths from the surface. Immediately after exposure to light, 100 μm thickness of resin composite was sectioned at the 1, 2, 3 and 4 mm from the top surface. The infrared spectrum of uncured resin and each wafer specimen were then obtained. The results were as follows: DC was significantly influenced by three variables of material, depth from the surface, and light source and energy level (P 〈 0·01). When the same light energy was irradiated, DC by plasma arc and LED was not significantly different from the halogen lamp (P 〉 0·05). When light energy was increased twice, no significant difference in DC was observed up to 2 mm from the surface (P 〉 0·05), but DC increased significantly from 3 mm (P 〈 0·05).
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 29 (2002), S. 0 
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: SUMMARY  The objectives of this paper were to evaluate the effects of colour measuring modes [specular component excluded (SCE) versus specular component included (SCI)] and the standard light source (C, A or D65) on the colour of shade guides. After the labial part of shade tabs of two shade guides (Vita and Chromascop) was polished flat up to no. 2400 silicone carbide paper, the colour was measured according to the International Commission on Illumination (CIE)L*a*b* colour scale on a spectrophotometer. In both shade guides, all the average CIE L* values of each shade series, and most of CIE b* values were different depending on the measuring mode (P 〈 0·01). However, there was no difference in CIE a* values depending on the measuring mode. Colour difference (ΔE*) between the values measured with SCE mode and with SCI mode was 3·21–6·50 in Vita shade guide, 3·22–5·47 in Chromascop shade guide. ΔE* caused by the difference in light source was very small in Vita shade guide regardless of the measuring mode. In the Vita shade guide, the shade series (A–D) was negatively correlated with CIE L* and CIE a* values measured with SCE mode. In the Chromascop shade guide, the shade series (100–500) was negatively correlated with CIE L* value measured with SCI mode.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of radioanalytical and nuclear chemistry 243 (2000), S. 525-533 
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A procedure is presented to provide sequential determination of isotopic strontium, thorium, plutonium, uranium, and americium in a single biological sample. The method begins with digestion and dissolution of the sample. Tracers and/or carriers are added to the sample for the purpose of chemical yield monitoring. Strontium is first separated from the actinides and from most of the interfering constituents of the sample by precipitation as carbonates. Strontium isotopes are purified, and 89Sr and 90Sr are measured by gas proportional counting. Actinides are separated and purified by ion exchange chromatography, co-precipitated with neodymium fluoride, filtered, and counted by alpha-particle spectrometry.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 35 (2000), S. 6035-6040 
    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 Can hydrogen trapped within the lattice of copper film produce irreversible effects on the electrical resistivities of copper film at room temperature? In order to answer this question, copper films were sputtered in the presence of hydrogen and resistivities were measured in vacuum at room temperature. A series of sputtering depositions were carried out at different hydrogen partial pressures to confirm irreversible hydrogen effects. Films sputtered in argon only, were used as controls. The electrical resistivities of copper films were measured as a function of hydrogen partial pressure. Saturation is reached for the electrical resistivity in high hydrogen partial pressures. The saturation is at around 5.0% hydrogen partial pressure of total sputtering pressure. The electrical resistivities of copper films are lowered irreversibly by hydrogen, because the films were sputtered in the gas mixtures of argon and hydrogen and the electrical resistivities of films were measured in the air. The sputtering rate decreases as the hydrogen partial pressure increases. The sputtering rate is found to be proportional to the average mass of the incident ion.
    Type of Medium: Electronic Resource
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  • 10
    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 Interfacial reactions in Al-0.5%wtCu/Ti/SiO2/Si structure have been investigated up to the annealing temperature of 600°C for 30 min in Argon ambient. Annealing temperature at above 500°C, Al alloy and Ti start to react and produce Al3Ti, which was already reported. Annealing at higher temperatures (550°C, and 600°C) made Al3Ti transformed into Al5Ti2, which is thermodynamically more stable than Al3Ti. The unreacted 52 nm thick Ti which existed underneath of Al5Ti2 might lead to retardation of the reaction between Al5Ti2 and the underlying SiO2. Hence, the formation of ternary compound (Al x Ti y Si z ) which is believed to be detrimental to the contact metallization layers was protected.
    Type of Medium: Electronic Resource
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