This study shows how treated filler loading influences the photopolymerization of a dimethacrylate comonomer mixture, regarding, in particular, shrinkage and inhibition under atmospheric oxygen, present in oral environment. Bis-GMA/TEGDMA (75/25 wt.%) resins were loaded with hybrid filler (Ba aluminosilicate glass and pyrogenic silica), treated with γ-methacryloxy(propyl)trimethoxysilane, at 0–50 wt.% and light cured over a total of 30 s (45 mW/cm2). Degree of double-bond conversion (DC), obtained using FTIR, decreased with filler content. 1H MAS spectra (293–340 K) and STRAFI images (293 K) were obtained as a function of irradiation time and filler concentration. 1H signals of unreacted methacrylate groups were more intense for higher loaded resins and resonances from –CH2SiO2(OH) (T2) and –CH2SiO3– (T3) units, also observed by 29Si NMR, were resolved and suggest the presence of T2–resin bonds. 1D images show a reduction on polymerization contraction and reaction inhibition at the composite resin surface with filler loading. 2D resin images present a highly mobile surface layer, hence with lower DC.
Nuclear Magnetic Resonance Composite Resin Nuclear Magnetic Resonance Spectroscopy Magic Angle Spin Filler Loading
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This work was supported by the Portuguese Foundation for Science and Technology (Grant: PRAXIS/BD/20066/99 and SFRH/BPD/25112/2005 and Projects: POCTI/33193/99 and PDCT/55395/04). The authors wish to thank KERR (USA) for kindly providing the filler.