Influence of photoinitiator type on the rate of polymerization, degree of conversion, hardness and yellowing of dental resin composites

Objectives To evaluate the degree of conversion (DC), maximum rate of polymerization (image), Knoop hardness (KHN) and yellowing (b-value) of resin composites formulated with phenylpropanedione (PPD), camphorquinone (CQ), or CQ/PPD at different concentrations. The hypotheses tested were (i) PPD or CQ/PPD would produce less image and yellowing than CQ alone without affecting DC and KHN, and (ii) image, DC, and KHN would be directly related to the absorbed power density (PDabs). Methods CQ/amine, PPD/amine and CQ/PPD/amine were used at low, intermediate and high concentrations in experimental composites. Photoinitiator absorption and halogen-light emission were measured using a spectrophotometer, Rp with differential scanning calorimetry (DSC), DC with DSC and FTIR, KHN with Knoop indentation; and color with a chromameter. The results were analyzed with two-way analysis of variance (ANOVA)/Student–Newman–Keulʹs test (p < 0.05). Correlation tests were carried out between PDabs and each of DC, image and KHN. Results The PDabs increased with photoinitiator concentration and PPD samples had the lowest values. In general, maximum DC was comparable at intermediate concentration, while image and KHN required higher concentrations. DC was similar for all photoinitiators, but image was lower with PPD and CQ/PPD. PPD produced the lowest KHN. Yellowing increased with photoinitiator concentration. PPD did not reduce yellowing at intermediate and/or high concentrations, compared to CQ-formulations. PDabs showed significant correlations with DC, image and KHN. Conclusion PPD or CQ/PPD reduced image in experimental composites without affecting the DC. The use of PPD did not reduce yellowing, but reduced KHN. DC, image and KHN were dependent on PDabs.