Abstract
Objective The aim of this investigation was to determine reaction enthalpy, ion viscosity and curing light transmission changes of unfilled methacrylate-based systems in order to compare methods that monitor photoactive resin polymerization. Methods Photoinitiator (0.2%, w/v, camphoroquinone), accelerator (0.3%, w/v, amine) and inhibitor (ranging from 0 to 1%, w/v, butylated hydroxytoluene, BHT) were incorporated in an experimental BisGMA/TEGDMA co-monomer mixture (50/50, w/v). The concentration of BHT was varied from 0.00, 0.01, 0.05, 0.10, 0.50 to 1.00% (w/v). Light transmission (LT), reaction enthalpy (UV-differential scanning calorimetry, DSC), and ion viscosity (dielectrical analysis, DEA) were determined during irradiation of the resins (40 s; halogen light curing-unit). Statistical analysis was performed using two-way ANOVA followed by post hoc tests ( α = 0.05). Curve fitting and regression calculation were done. Results There was no significant change in the time to reach the maximum rate of polymerization (reaction time) in the individual systems up to a BHT concentration of 0.05% ( P > 0.05). Starting at a concentration of 0.10% BHT an increase in time of reaction could be found from 4.0 s (LT), 4.07 s (DEA) and 4.9 s (DSC) to a maximum of 7.4 s (DSC), 9.43 s (DEA) and 9.67 s (LT). Linear increase ( y = 5.588 × x) in time to the maximum speed of reaction could be found with a correlation of R 2 = 0.992. Conclusions The speed of polymerization reaction is strongly influenced by BHT concentration. The linear relationship should allow for the prediction of the speed of reaction during blending of a methacrylate-based resin. The three test systems allow for monitoring the complex polymerization kinetics of unfilled methacrylate-based systems.
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