Conversion of resins with different amine:camphorquinone ratios and concentrations

OBJECTIVES: Evaluate how the degree of conversion (DC) of experimental resins is affected by the total concentration of the photoinitiator system as well as by the ratio between its elements (amine:camporquinone).

METHODS: BisGMA/TEGDMA/UDMA (1:1:1 mols) were mixed with 0.1mol% BHT and five photoinitiator concentrations: 0.5; 1.0; 1.5; 2.0 and 3.0 mol%. At each of these overall concentration levels, DMAEMA (amine) and camphorquinone (CQ) were combined in one of the following molar ratios: 3:1, 2:1, 1:1, 1:2 and 1:3, in a total of 25 experimental groups. Ten bars (10x2x1mm) were prepared for each material using a silicon mold. Specimens were photoactivated (600mW/cm²x40s) and stored in the dark for 24h at 37oC. DC (%) was evaluated with FT-Raman spectroscopy. Results were submitted to two-way ANOVA and Tukey's test (α=5%).

RESULTS: The interaction between the factors was significant (p<0.05). For the lowest concentration (0.5%), 3:1 ratio resulted in lower DC (41±7%) compared to the other groups (between 60±4% and 67±3%). For concentrations of 1.0% and 1.5%, DC varied between 59±5% and 80±3% and the excess amine allowed for values statistically higher than the lowest found for these concentrations. For 2.0%, DC did not vary with the ratio, except for 1:3. For the highest concentration (3.0%), all ratios led to statistically similar DC values (between 70±4% and 77±4%). The 3:1 ratio presented the highest DC above 1% amine/CQ. For 2:1, DC was different from the lowest values above 1.5% total concentration. For 1:1 and 2:1, this was only observed above 3.0%.

CONCLUSION: For total initiator concentrations of 2% and 3%, the maximum DC of the experiment was attained at all amine:CQ ratios. For 0.5% final concentration, a minimum absolute CQ concentration was necessary so that the DC was not jeopardized. For the intermediate concentrations, in general, higher amine ratios led to better DC results.