In dental composites, the presence of inorganic fillers in the organic matrix leads to a light-scattering phenomenon that modifies the light intensity and, consequently, the ultimate polymerization yield. In this study, we aimed to characterize the impact of light scattering on the photopolymerization profiles inside thick materials. First, the photopolymerization kinetics of dental composites containing alumina or zirconia nanofillers were studied. An optimal formulation based on 75 wt% Bis-GMA, 25 wt% triethyleneglycoldimethacrylate and 1 wt% camphorquinone/dimethylaminoethylmethacrylate (1/1) was determined. The compatibility between the organic matrix and the fillers was enhanced by grafting a silane coupling agent onto the surfaces of the nanoparticles. This grafting improved the mechanical properties of the final composites without modifying the photopolymerization kinetics. The presence of nanofillers leads to a light-scattering phenomenon that influences the photoinitiated polymerization yield inside the composite. Thus, to characterize this phenomenon, a four-flux radiative transfer theory was applied to calculate the decrease in the light intensity crossing the dental composite. The conversion profiles were then calculated and compared with experimental ones.
"Organosilanes bearing alkoxysilane are widely used in sol-gel process. In this process, the hydrolysis reaction is usually carried out in aqueous or hydroalcoholic solutions and the condensation reaction requires high temperatures. The hydrolysis of the alkoxysilanes in the presence of water is fast and can be considered as complete. The obtained silanols can then condensate into oligomers by a much slower reaction that depends on temperature. Our objective is to devise a simple synthesis way for grafting such coupling agent onto the mineral fillers surface without using solvent and heating. Mineral fillers are used as reinforcement in dental composites based on Bis-GMA/TEGDMA. The way developed in this work involves a photoinitiated sol-gel process. It consists in using a photoacid generator to activate the hydrolysis and condensation reactions under atmospheric humidity. Mineral oxides usually used in dental materials were chosen as inorganic filler: the zirconia (ZrO2) which is a radiopacifiant agent and the alumina (Al2O3) which allows improving the mechanical properties of the composite. A kinetic study of the self-condensation of the 3-MPS used as coupling agent in the presence of Irgacure 250 ® as photoacid generator was carried out and the operating conditions (irradiation intensity and time) of the functionalization reaction were optimized. Grafted fillers were characterized by FTIR spectroscopy and thermogravimetic analysis. FTIR and TGA analyses of the particles after treatment allow confirming the grafting. Compared to the conventional way, the photoinitiated process proves to be faster, easier, less expensive in energy, and much more efficient in terms of 3-MPS grafted quantity. "
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.
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