Polymerization Kinetics of Experimental Resins: Effect of Composition and Light-Curing

Objectives: The aim of this study was to evaluate the effect of the resin matrix and photoinitiator type on polymerization kinetics, conversion rate and degree of conversion (DC) of experimental resins photocured using LED and halogen (QTH) light curing units (LCU). Spectrum and intensity of the light of the LCU were also evaluated. Methods: Experimental resins containing 50wt% BisGMA and 50wt% TEGDMA (BT) or 29wt% BisGMA, 32wt% BisEMA, 32wt% UDMA and 7wt% TEGDMA (BBUT) were prepared in combination with the photoinitiators: CQ (Camphorquinone), PPD (1-Phenil-1,2-Propanodione) or both (CP). Photoactivation was performed using the LCUs XL3000 (QTH) and Radii (LED). A power meter and a spectrometer (USB 2000) were used to analyze total irradiance and wavelength spectrum distribution. Absorption curves of CQ and PPD were evaluated using a spectrometer (Varian Cary 5G). Real-time Fourier transform infrared spectroscopy (Shimadzu Prestige21) was used to assess the polymerization reaction over time (50s). Data were plotted, and Hill's three-parameter nonlinear regression was performed for curve fitting. DC at each second was calculated and curves DC x time were obtained. Results: Polymerization kinetics is significantly affected by all factors (LCU, resin matrix and photoinitiator). The matrix BBUT, photoinitiator CQ and LCU QTH produced higher polymerization speed. The combination BBUT/CQ showed higher conversion rate, it showed DC of 42% after 20s of photoactivation whereas BT/PPD after 20s showed DC of 24%. After 50s, the highest final values of DC were observed in the resins BT/CQ (56%) and BBUT/CQ (52%) and the lowest values were observed in the resins BT/CP (40%) and BT/PPD (43%) Conclusion: The resin matrix and the photoinitiator type interfere in the polymerization kinetics of resin materials. The composition is determinant on the conversion rate and DC. Polymerization speed of resins is reduced when they are activated using LED LCU.