Microareas (100×100μm²) of thin visible light-cured composite sections irradiated for 10-60s were analyzed with a Fourier transform infrared spectrometer equipped with a microscopic unit before and after extraction of residual monomers to determine the percent unreacted double bonds (UDB) and percent pendant double bonds (PDB). The percent eluted double bonds (EDB) was calculated using these percents. Analysis was conducted at various depths along the midline from the irradiated surface to the base.
There were significant differences among the tested materials at each depth in UDB, PDB and EDB percents. The percent PDB of each material remained almost constant (25-40%) to a certain depth. This depth was equivalent to 70-80% of the depth of cure for each material. The range of depths at which percent PDB was constant indicated greater than 35-40% degree of conversion. At these locations, the composites may polymerize with a high rate of crosslinking.