IADR Abstract Archives
Irradiance Reciprocity Studies in Resin and Composite Photopolymerizations
Objectives: Prior studies have shown that optically transparent, thin films do not obey the reciprocity model, which requires conversion profiles obtained at different irradiance levels collapse to a uniform profile when correlated with applied photon dose. This study examines potential reciprocity behavior of resin and composite materials of varied thickness during photopolymerization at different irradiance levels.
Methods: BisGMA/TEGDMA resins containing CQ/amine were used at specimen thicknesses of 0.1-1.5mm. Composite specimens were prepared with 65wt% silane-treated barium glass. A radiometer provided incident irradiance values that were controllably varied from ~15 to 675mW/cm2. Temperature change was measured by embedded thermocouple. Real-time near-IR provided conversion vs time data that was transformed to reaction rate vs either time or photon dose. Real-time UV-Vis spectroscopy followed dynamic light transmission.
Results: Time-based reaction kinetic plots clearly demonstrate expected rate enhancement with increasing irradiance with thicker specimens consistently producing higher rates due to greater exotherm. Higher final conversion was reached with unfilled vs filled resins. In most cases, intermediate conversion relative to photon dose follows an inverse relationship with respect to irradiance. This association was less well defined for composites especially thicker composites. In medium thickness (0.8mm) unfilled resin at a dose of 2000mJ/cm2, conversion values of 52.6, 44.9 and 12.5% were achieved using 25, 160 and 675mW/cm2 irradiance, respectively; however, some overlap in conversion was noted for certain irradiance ranges. Composite materials showed more efficient use of early-stage photons at high irradiance; i.e. the 0.8mm composite at 2000mJ/cm2 reached 19.8% conversion. Unfilled materials show minimal reduction in transmitted light intensity during polymerization while light transmission increases through a maximum with filler present, which adds complexity especially to thick composite specimens.
Conclusions: In both unfilled and filled materials, there are some limited examples of photopolymerizations that demonstrate reciprocity behavior but this appears due to secondary effects of temperature and light transmission.
Methods: BisGMA/TEGDMA resins containing CQ/amine were used at specimen thicknesses of 0.1-1.5mm. Composite specimens were prepared with 65wt% silane-treated barium glass. A radiometer provided incident irradiance values that were controllably varied from ~15 to 675mW/cm2. Temperature change was measured by embedded thermocouple. Real-time near-IR provided conversion vs time data that was transformed to reaction rate vs either time or photon dose. Real-time UV-Vis spectroscopy followed dynamic light transmission.
Results: Time-based reaction kinetic plots clearly demonstrate expected rate enhancement with increasing irradiance with thicker specimens consistently producing higher rates due to greater exotherm. Higher final conversion was reached with unfilled vs filled resins. In most cases, intermediate conversion relative to photon dose follows an inverse relationship with respect to irradiance. This association was less well defined for composites especially thicker composites. In medium thickness (0.8mm) unfilled resin at a dose of 2000mJ/cm2, conversion values of 52.6, 44.9 and 12.5% were achieved using 25, 160 and 675mW/cm2 irradiance, respectively; however, some overlap in conversion was noted for certain irradiance ranges. Composite materials showed more efficient use of early-stage photons at high irradiance; i.e. the 0.8mm composite at 2000mJ/cm2 reached 19.8% conversion. Unfilled materials show minimal reduction in transmitted light intensity during polymerization while light transmission increases through a maximum with filler present, which adds complexity especially to thick composite specimens.
Conclusions: In both unfilled and filled materials, there are some limited examples of photopolymerizations that demonstrate reciprocity behavior but this appears due to secondary effects of temperature and light transmission.