Effects of Sn, Ga, and In additives on properties of Ag-Pd-Au-Cu alloy for ultra-low fusing ceramics. (17/634)

Nine 35% Ag-30% Pd-20% Au-15% Cu alloys containing 2, 4 and 6 mass% of Sn, Ga or In as an additive metal were experimentally prepared to investigate the effects of different additives and their content on the physical and mechanical properties as well as the bond with a ultra-low fusing ceramic. Both the different additives and their content or either of these two factors significantly influenced most of the evaluated properties except for the area fraction of the retained ceramic. Based on the evaluated properties three experimental alloys (2% Sn-added alloy, 4% Ga-added alloy and 2% In-added alloy) can be recommended as a suitable alloy for ceramic-metal restorations using ultra-low fusing ceramics.  (+info)

Radiation effects of carbon ions and gamma ray on UDMA based dental resin. (18/634)

The radiation effects on the mechanical and physical properties of photo-polymerized UDMA resin without filler was investigated by various mechanical tests and spectroscopic measurements. The radiation sources were carbon ion (12C ion) and gamma ray (gamma-ray). With 640 Gy of 12C ion radiation, Vickers hardness increased by about 40%, the degree of abrasion decreased by 30%, and the flexural strength increased by 20%. With the same dose of gamma-ray radiation, only Vickers hardness increased by 19%. The spectra taken by the Fourier Transform Infrared Spectrometer (FT-IR), Raman spectroscopy, and Fluorescence spectrophotometer showed little change in the peak configuration and background intensities. The relative degree of conversion (DC) of carbon double bonds by radiation to the state of non-radiated samples were estimated by FT-IR. Spectroscopic results were indicative for the formation of cross-linking between carbon chains. Cross-linking of carbon molecules induced by radiation might be one of the reasons for the improved mechanical properties of UDMA resin.  (+info)

Efficacy of dentin bonding to cervical defects. (19/634)

The bonding efficacy of sclerotic dentin was determined by measuring the polymerization contraction gap width of a commercial light-activated resin composite in a cervical defect and by measuring the micro-Vicker's hardness at the dentin adhesive surface; morphological characteristics were observed using a scanning electron microscope in extracted human incisors and premolars. Contraction gap formation was completely prevented when the cavity wall was primed with 35 vol% glyceryl mono-methacrylate solution after 0.5 mol/L EDTA conditioning. The contraction gap width was significantly decreased when the resin composite was filled into the sclerotic dentin cavity even when priming was omitted. These results suggest that the sclerotic dentin, which is frequently observed in cervical defects, should be preserved as a substrate because it exhibits an effect of dentin priming and is suitable for bonding.  (+info)

The relationship between nuclear colour and opalescence on the LOCSIII scale and physical characteristics of cataract nuclei. (20/634)

PURPOSE: To evaluate the compression characteristics of the human lens nucleocortex in relation to its LOCSIII clinical grading. METHODS: Sixteen subjects undergoing planned extracapsular cataract surgery had pre-operative slit-lamp examination and assessment of cataract LOCSIII grade followed by postoperative in vitro evaluation of the nucleus with measurement of 'linear compressibility' by a purpose-designed caliper incorporating a strain gauge, enabling the derivation of a graph of nuclear compression (D (mm) against applied force (F (N)). RESULTS: Nuclear colour correlates with the force required to compress a lens to 75% of its original depth (F75) (R = 0.625, P = 0.017). Nuclear opalescence correlates with the force required to compress a lens to 75% of its original depth (R = 0.651, P = 0.012) and inversely with linear compressibility (DeltaD/DeltaF, the slope of the graph of nuclear compression against applied force) (R = -0.610, P = 0.014). F75 is a direct and linear compressibility is an inverse related parameter of lens nucleus 'hardness'. CONCLUSION: A new instrument is described which allows measurement of 'hardness'-related compression characteristics of the human cataract in vitro. There is a relationship between the LOCSIII clinical classification of nuclear cataracts and mechanical compression characteristics of the cataractous lens. LOCSIII classification may aid the preoperative planning of an appropriate surgical approach to an individual cataract.  (+info)

Mechanical properties of light-cured composite resins cured through filters that simulate enamel. (21/634)

The light-attenuating effects of enamel on the mechanical properties of light-cured composite resins were evaluated using simple experimental filters. Three filters were designed to simulate the light transmittance characteristics of 0.5, 1.0, and 1.5 mm thick human enamel. The Knoop hardness numbers (KHN) and the elastic modulus in transverse tests for twelve shades of three light-cured composite resins were examined. These resins were cured either using direct irradiation with a light source, or indirect irradiation through one of the filters. The attenuations of light by 0.5, 1.0, and 1.5 mm thick enamel filter were 45%, 67% and 81% in the 430 nm-550 nm wavelength region, respectively. For all materials, KHN and the elastic modulus of specimens irradiated through filters were significantly lower than those irradiated directly. The results suggest that the light-attenuating effect of enamel reduces the mechanical properties of light-cured resin, and may cause poor clinical longevity of restorations.  (+info)

High abrasion resistance with sparse mineralization: copper biomineral in worm jaws. (22/634)

Biominerals are widely exploited to harden or stiffen tissues in living organisms, with calcium-, silicon-, and iron-based minerals being most common. In notable contrast, the jaws of the marine bloodworm Glycera dibranchiata contain the copper-based biomineral atacamite [Cu2(OH)3Cl]. Polycrystalline fibers are oriented with the outer contour of the jaw. Using nanoindentation, we show that the mineral has a structural role and enhances hardness and stiffness. Despite the low degree of mineralization, bloodworm jaws exhibit an extraordinary resistance to abrasion, significantly exceeding that of vertebrate dentin and approaching that of tooth enamel.  (+info)

Wear resistance of hybrid composite resin for crown material by the two-body sliding test. (23/634)

Comparative studies on two-body sliding wear resistance were performed between a hybrid composite resin and conventional light-curing composite veneering materials. This study investigated the wear resistance of hybrid composite resins compared with three composite resin veneering materials for 12%Au-Ag-Pd alloy, the wear resistance of four restorative materials opposed to hybrid composite resin, and the influence of surface characteristics on hybrid composite resins. Hybrid composite resin without heat-curing, which was compared with other composite resin materials exhibited inferior wear resistance, but hybrid composite resin mechanically polished after heat-curing exhibited the most superior wear resistance.  (+info)

Mechanical properties of reinforced denture base resin: the effect of position and the number of woven glass fibers. (24/634)

This study examined the effects of the position and the number of woven glass fibers on the flexural strength, flexural modulus, and toughness of reinforced denture base resin. The woven glass fiber consisted of 1-4 laminated sheets. Chemical curing was used to polymerize three types of 4-mm-thick test specimens: fibers in compresrion, fibers in the center, and fibers in tension. Unreinforced specimens were produced as controls. A three-point flexural test was performed and the woven glass fiber content was calculated after the woven glass fiber was fired. The best results were obtained when the woven glass fiber was incorporated outside the base resin under tension, thereby increasing the flexural strength and flexural modulus. Furthermore, the denture base resin reinforced with woven glass fiber was made tougher by increasing the number of woven glass fibers incorporated into the portion under tension.  (+info)