Determination of degree of conversion as function of depth of a photo-initiated dental restoration composite

The degree of conversion (DC) of a commercial photo-activated dental composite at different depths evaluated by a reliable method, Fourier transformation infrared spectroscopy (FT-IR), is reported. The polymerization reaction was carried out in cylindrical specimens with depth from 1 to 5 mm using a halogen light curing unit (450 nm, 21,200 J/cm2). FT-IR spectra of the material before and after the cure reaction were taken and the ratio of heights between absorptions at 1637 cm−1 (variable) and 1610 cm−1 (reference) was used to determine DC. The DC showed a tendency to decrease with increasing depth, attaining values in the range of 40-50%. The low values of DC indicated that a large amount of residual monomer has remained. The factors that could contribute to decreasing of DC were the monomers viscosities and ratio, size of fillers and great difference in refractive indices of organic and inorganic constituents. Additionally, the composite formulation was investigated by commonly used techniques, such as, thermogravimetry (TGA), X-ray fluorescence (XRF), light scattering (LS) and proton-nuclear magnetic resonance (1H NMR). The composite is composed of: 78.6% inorganic fillers, 20.6% BisfenolA/dimethacrylate (BisGMA) and 0.8% triethyleneglycoldimethacrylate (TEGDMA) as monomers.