Measurement of shrinkage during photopolymerization of a model dental resin based on dimethacrylate monomers

V. MUCCI; C. VALLO

Ghent- Belgium

Simposio; Baekeland 2007 Symposium Thermosets, 100 years after Bakelite; 2007

Ghent University

Light-activated dental composites are widely used in clinical restorative dentistry. However, they exhibit the inherent problem of volumetric shrinkage during the polymerization process, which results in the development of internal stresses. Various curing procedures have been proposed to minimize the shrinkage of dental composites.1-2 The purpose of this investigation was to study the influence of the photopolymerization procedure on the shrinkage evolution of a methacrylate-based dental resin. The resins were formulated from blends of {2,2-bis[4- (2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane} (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) at mass fractions 70:30 Bis-GMA/TEGDMA. The resins were activated for visible light polymerization by the addition of camphorquinone (CQ) and Dimethylamino ethylmethacrylate (DMAEMA). The resins were photopolymerized with a Light Emitting Diode (LED) centred at 470 nm. The light intensity was 7.7 mW/cm2 . A fibre optic sensing method based on a Fizeau-type interferometric scheme was employed for monitoring the evolution of the shrinkage during photopolymerization. Figure 1 depicts the experimental setup.  Details of the technique were reported elsewhere.3 The percent of the linear contraction was calculated DL/L0, where DL is the separation of the reflective faces measured from the interferogram and L0 is the initial thickness of the sample. FTIR spectra were acquired over the range 4500-7000 cm-1 from 16 co-added scans at 2 cm-1 resolution.   The conversion profiles were calculated from the decay of the absorption band located at 6165 cm-1.