Browsing by Author "Yamuna, V"

Now showing 1 - 5 of 5
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    Aging studies of a radiopaque light-cured dental composite in food-simulating liquids
    (JOURNAL OF APPLIED POLYMER SCIENCE, 1998) Krishnan, VK; Yamuna, V
    Sorption behavior and changes in physical properties of an indigenously developed radiopaque light-cured dental composite upon aging in citrate buffer (pH: 4.0), 50% ethyl alcohol and saline for a total period of 80 days, have been studied. Water uptake into the composite reaches saturation within 14 days in all media, whereas solubility values show an upward trend even after storage for 80 days. Solubility in alcohol medium is found to be high compared to saline and citrate media. Compressive strength and diametral tensile strength measurements tend to increase initially and then decrease gradually with time due to degradation of the composite upon storage. However, this reduction Is not appreciable, as indicated by the strength values after 80 days, which are higher than the mandatory 220 MPa for CS and 34 MPa for DTS. Microhardness increases with time in all three cases, although alcohol medium tends to soften the material, resulting in an initial sharp decrease. (C) 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1153-1158, 1998.
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    Effect of diluent upon the properties of a visible-light-cured dental composite
    (JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 1997)
    Four long-chain aliphatic organic diluents, triethylene glycol dimethacrylate (TEGDMA), ethylene glycol dimethacrylate (EDMA), triethyleneglycol diacrylate (TEGDA) and tetraethylene glycol diacrylate (TTEGDA) were used as diluents for preparing a visible-light-cured dental composite. Cured samples of pastes prepared using the above diluents were stored separately for a period of 60 days in distilled water at 37 degrees C and tested for changes in compressive strength, diametral tensile strength and microhardness at specific intervals of 1, 7, 14, 21, 28 and 60 days. Samples prepared using TEGDMA showed better strength values initially compared with the composite specimens prepared using the rest of the diluents although they are found to deteriorate slowly upon storage in distilled water up to 60 days. Samples prepared using EDMA showed retention in properties whereas samples prepared using TEGDA and TTEGDA showed large deviations in strength values during the first 28 days, did not deteriorate further and were found either to show improvement upon ageing or to remain constant. Sorption values seem to reach a maximum for all composites and then to decrease further after 14 days whereas solubility is found to increase with time.
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    Effect of initiator concentration, exposure time and particle size of the filler upon the mechanical properties of a light-curing radiopaque dental composite
    (JOURNAL OF ORAL REHABILITATION, 1998) Krishnan, VK; Yamuna, V
    Concentration of camphorquinone initiator, exposure time of the light source and particle size of a radiopaque glass filler have been varied for an indigenously developed light-curing dental composite and the changes in the microhardness, compressive strength and diametral tensile strength studied. Higher initiator concentration and exposure times are found to improve the microhardness values while a concentration above 0.25% does not signify any drastic improvement in compressive and diametral strength. Changes in properties are found to be statistically significant at low initiator concentrations. A filler particle size around 1 mu m is found to give better properties compared with larger sizes.
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    Effect of initiator concentration, exposure time and particle size of the filler upon the mechanical properties of a light-curing radiopaque dental composite.
    (Journal of oral rehabilitation, 1998)
    Concentration of camphorquinone initiator, exposure time of the light source and particle size of a radiopaque glass filler have been varied for an indigenously developed light-curing dental composite and the changes in the microhardness, compressive strength and diametral tensile strength studied. Higher initiator concentration and exposure times are found to improve the microhardness values while a concentration above 0.25% does not signify any drastic improvement in compressive and diametral strength. Changes in properties are found to be statistically significant at low initiator concentrations. A filler particle size around 1 microm is found to give better properties compared with larger sizes.
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    Evaluation of a light cured dental composite containing a radiopaque glass filler
    (CURRENT SCIENCE, 1997) Krishnan, VK; Yamuna, V
    Light curing dental composite pastes were prepared using an indigenously developed Bisphenol A-glycidyl methacrylate (BIS-GMA) resin and a commercially available radiopaque glass filler of different particle sizes. SEM examination of the virgin filler and composite surface revealed agglomeration of particles in virgin state and fine encapsulation of the filler particles in resin matrix of composite. Variation of the filler content shows that an amount of 220 phr (parts per hundred of resin mixture) of the radiopaque glass filler of larger grain size or 250 phr of the smaller grain size incorporated into the paste tends to improve the compressive strength and diametral tensile strength considerably compared to composite containing conventional quartz fillers.