Calibration of FTIR conversion analysis of contemporary dental resin composites

Composite restorative material has undergone gradual change in composition since its introduction in the 1960's. Early commercial resins were mixtures of BIS-GMA and TEGDMA. Today, these mixtures are still present, but urethane dimethacrylates and large oligomeric structures of BIS-GMA-urethanes exist. Because of these changes in composition, the past methods of calculating monomer conversion by means of infrared spectroscopy may need modification. This research investigates different methods used to formulate calibration curves for determination of monomer conversion by infrared spectroscopy of contemporary commercial composites containing aromatic structures. Conversion calibration procedures using various baseline methods with BIS-GMA, Bisphenol-A/TEGDMA, and a hydrogenated bonding resin were established. Both peak and area infrared absorptions were determined. One particular baseline method proved the best fit to the Beer-Lambert law. Bisphenol-A was found unsuitable as an infrared calibration model for resin composites. The BIS-GMA/TEGDMA calibration model closely simulates conversion values obtained when a hydrogenated commercial resin model was used.