Photoinitiator Concentration and Modulated-Photoactivation: Influence on Polymerization Characteristics of Experimental-Composites

Objectives: The aim of this study was to determine the influence of photoinitiator concentration on polymerization characteristics of experimental composites photocured by different methods. Methods: Composites based on BisGMA/TEGDMA and 65% of BaAlSi/SiO2 filler were prepared with different concentration of photoinitiators (C1-0.5%, C2-1%, C3-1.5%) and photocured using 4 methods (Energy dose: 30J): High-intensity (HI-750mW/cm2 for 40s), Low-intensity (LI-150mW/cm2 for 200s), Soft-start (SS-150mW/cm2 for 10s + 750mW/cm2 for 38s) and Pulse-delay (PD-150mW/cm2 for 5s + 3min light-off + 750mW/cm2 for 39s). Degree of conversion (DConv) was determined by Fourier Transform Infrared Spectroscopy (FTIR) (n=3). Depth of cure (DCure) was determined in cylindrical specimens by Knoop hardness measurements (KHN) obtained on surface, 1mm, 2mm, 3mm and 4mm depths (n=5). An indirect evaluation of crosslink density (CLD) was performed in cylindrical specimens by hardness measures before and after storage in absolute ethanol for 24h (n=10). Data were submitted to ANOVA and Tukey's test (p<0.05). Results: The evaluation of DConv and DCure revealed that there was no difference among the photoactivation methods. C3 and C2 showed significant higher DConv than C1, regardless of the photoactivation method. DCure obtained was 2 mm for C2 and C3, and 1mm for C1. In deeper regions, KHN showed significant reduction. The CLD evaluation revealed considerable differences among the photoactivation methods: HI>PD=SS=LI. Conclusions: Photoinitiator concentration is a determinant factor in the polymerization characteristics of composites. The composite with photoinitiator concentration of 0.5% presented reduction in DConv and in DCure, when compared with the composites with higher concentrations (1% and 1.5%). Photoactivation methods had no effect on the DConv and DCure, as the same amount of energy was used for all methods. However, the application of modulated methods (SS, PD) and LI produced composites with low CLD when compared to HI (Financial Support: FAPESP 07/53764-70).