Shrinkage strain – Rates study of dental composites based on (BisGMA/TEGDMA) monomers

AbstractThe viscosity of the initial monomer mixture and the chemical structure of the monomers are both important variables in the kinetic behavior of resin composites. This paper aims to determine the effect of opaque mineral fillers and monomer ratios on the shrinkage strain-rate and time at maximum shrinkage strain (Smax) rate, of experimental composites based on (BisGMA/TEGDMA) monomers. Polymerization shrinkage and the degree of conversion (DC) of resin composites are closely related manifestations of the same process. The proportionality of these two properties was also investigated by studying the variation of the ratio: (total shrinkage strain/degree of conversion): (Smax/DC), as a function of mineral filler contents and monomer ratios.Resin composites were prepared by mixing different monomer ratios of (BisGMA/TEGDMA) with camphoroquinone and dimethyl aminoethyl methacrylate (DMAEMA) as photo-initiator system. Five different radiopacifying filler agents: La2O3, BaO, BaSO4,·SrO and ZrO2 at various volume fractions ranging from 0 to 80wt.% were added. The samples were cured at ca. 550mW/cm2. The shrinkage strain-rate, was calculated from the derivative of shrinkage strain using numerical differentiation. The shrinkage strain was measured by the bonded-disk technique at room temperature. Degree of conversion was calculated using FTIR/ATR spectroscopy.The results revealed that the fraction of opaque filler had no significant effect on the shrinkage strain-rate and on the time at maximum shrinkage strain-rate but these two parameters are closely related to the monomer ratios and viscosity of the organic matrix. The results have confirmed the proportionality of the shrinkage strain and DC and showed that the filler contents and monomer ratios would not affect this proportionality

Photoinitiated polymerization of a dental formulation: 1. Influence of photoinitiating system, temperature and luminous intensity

The photoinitiated polymerization of a dental formulation is composed of Mixture of monomers 75%Bis-GMA/25%TEGDMA and CQ/DMAEMA as radical photoinitiator was studied by using isothermal photocalorimetry. The effect of temperature, light intensity and photoinitiating system concentration on reaction was investigated. A maximum conversion was obtained for a photoinitiator system concentration of 1% (w/w) and for the highest light intensity studied. It should be noted that a correlation between the glass transition temperature of the final polymer and the conversion has been studied.Keywords: dental composite; photopolymerization; dimethacrylate resin; photoinitiator syste

Enabling planetary science across light-years. Ariel Definition Study Report

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution