Photobleaching of camphorquinone during polymerization of dimethacrylate-based resins

SILVANA ASMUSEN ; GUSTAVO F. ARENAS; WAYNE D. COOK; CLAUDIA I. VALLO

DENTAL MATERIALS

ELSEVIER SCI LTD

Año: 2009 vol. 25 p. 1603 - 1611

0109-5641

Objective. The aim of this study was to compare the photobleaching rate of CQ in differentdental resins.Methods. The photodecomposition rate of CQ/amine system in bis-GMA/TEGDMA, bis-EMAand UDMA polymerizing monomers was evaluated at different light intensities. The photobleachingof the CQwas studied by monitoring the decrease in light absorption as a functionof continuous irradiation time. The absorption changes were assessed by recording thetransmitted light that passed through samples of monomers containing CQ/amine.Results. Complete photobleaching of CQ was observed in all the monomer tested and therate constant for the photobleaching was proportional to the radiation intensity. Hydrogenabstraction from amines by the excited CQ state via electron transfer and direct hydrogenabstraction from monomer structures were involved in the CQ photoreduction. CQwas photobleached in the absence of coinitiator in a dimethacrylate monomer containinga carbamate functional group (UDMA). This behavior was attributed to the presenceof labile hydrogen atoms in the UDMA monomer. The CQ photobleaching rate constant inUDMAcontaining CQ/aminewas similar to that inUDMAin the absence of amine.Moreover,the efficiency of CQ to photoinitiate the polymerization of UDMA in the absence of aminedemonstrated that the radicals derived from the UDMA monomer via hydrogen abstractionare highly reactive toward double bonds.Significance. CQ photoinitiates the polymerization of the UDMA monomer in the absence ofamine and the efficiency of this process is comparable to that of traditional bis-GMA andbis-EMA monomers activated with CQ/amine.