Abstract
Experimental dental resins composed of triethyleneglycol dimethacrylate, urethane dimethacrylate, ethoxylated bisphenol-A-dimethacrylate and bisphenol A glycidyl methacrylate containing an organoclay as filler were prepared by photopolymerization. The addition of organoclay fillers results in slower polymerization rates (0.59 and 0.24 mol L-1 min-1, for the formulations without and with 15% of organoclay, respectively) and lower degrees of conversion (0.50 and 0.35 for the formulations without and with 15% of organoclay), as determined by photocalorimetry. The influence of the organoclay on the thermal and mechanical properties of the resins was evaluated using thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) techniques. The (tan δ) and E´ curves indicate the formation of more rigid materials and the damping curve data indicates more homogeneous materials. An increase of storage modulus, E’, was observed for composites with the higher organoclay filler contents. These effects are due to the higher viscosity of the systems with organoclay, resulting in a lower mobility of the radicals during the propagation step of polymerization, as well as to the scattering of the incident photopolymerizing radiation, which lowers the amount of initiation centres.
Highlights
Polymeric composites containing inorganic fillers cured by visible light are commonly used as filling materials in dental restorations
The use of organoclays as fillers in dental resin composites was tested, and from the results obtained, it seems to be a potential component for improving the properties of these materials
TGA and DTG experiments indicate that the polymers obtained from samples with no organoclay addition are non-homogeneous: the plot shows two peaks, whereas the addition of 5-15% decreases significantly the lower temperature peak
Summary
Polymeric composites containing inorganic fillers cured by visible light are commonly used as filling materials in dental restorations. The composition of these materials contains 75 - 85% (w/w) of inorganic material and 15-25% of a polymeric matrix based on dimethacrylate monomers.[1] The shrinkage of the polymeric material,[1,2] which occurs during the polymerization process, may result in a loss of resistance and formation of creases. Degradation of the organic matrix is enhanced at these sites, as well as undesired sorption of oral fluids. The inorganic fillers, silica or quartz, are added to improve the mechanical properties of the restoration. Hardness, thermal expansion coefficient, wear resistance, sorption processes and polymerization shrinkage are all dependent on the filling and the coupling agents.[3,4]
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