Photopolymerization kinetics of dimethacrylate-based light-cured dental resins

The influence of certain factors [structure and concentration of tertiary amines as coinitiators, monomer composition, presence of inorganic pigments, and incident light intensity (I-0)] on the polymerization rates (R-p), polymerization quantum yields, and conversions of bisphenol A-bis(glycidyl methacrylate) (Bis-GMA)/triethylene glycol dimethacrylate based resins was studied. The initial rate of bulk polymerization increased and the final conversion decreased with the content of Bis-GMA in the mixture. In contrast, it was established that, for all monomer compositions, the R-p, grew when increasing the I-0, the R-p, being directly proportional to the square root of I-0. Such behavior is in agreement with the well-known kinetic expression for the ideal radical photoinitiated polymerization in solution of monofunctional monomers, in spite of the complexity of the dimethacrylate mixtures that were studied. Both the structure and the concentration of reducing amine affected the efficiency of the initiator system and therefore the kinetic behavior of polymerization of these formulations under irradiation. The rate of polymerization increased with the increase of coinitiator concentration over the interval of 0-1%, but later it diminished when increasing the amine content, suggesting that the excess coinitiator retards the polymerization process. The study of the photoreduction of camphorquinone in the presence of different amines showed that the efficiency of the coinitiator depends not only on its ability to photoreduce camphorquinone, forming amine-derived radicals, but also on the reactivity of these radicals toward the initiation of acrylic monomer polymerization. (c) 2005 Wiley Periodicals, Inc.