Relationship between the degree of conversion and internal discoloration of light-activated composite.

In order to elucidate the relationship between the degree of conversion and internal discoloration of light-activated composite, four experimental composites which contained different amounts of Bis-GMA and TEGDMA were prepared, and the degree of conversion and discoloration of each composite, with or without annealing, were determined. The degree of conversion was measured by Fourier transformation infrared spectroscopy and the color change was determined after 1, 2, 3 and 4 weeks of immersion in water at 60 degrees C. The non-annealed composites demonstrated a greater degree of conversion and less discoloration as the amount of TEGDMA was increased.