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

Abstract

Objectives To evaluate the degree of conversion (DC), maximum rate of polymerization ( R p max ), 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 R p max and yellowing than CQ alone without affecting DC and KHN, and (ii) R p max , DC, and KHN would be directly related to the absorbed power density (PD abs). 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, R p 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–Keul's test ( p < 0.05). Correlation tests were carried out between PD abs and each of DC, R p max and KHN. Results The PD abs increased with photoinitiator concentration and PPD samples had the lowest values. In general, maximum DC was comparable at intermediate concentration, while R p max and KHN required higher concentrations. DC was similar for all photoinitiators, but R p max 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. PD abs showed significant correlations with DC, R p max and KHN. Conclusion PPD or CQ/PPD reduced R p max in experimental composites without affecting the DC. The use of PPD did not reduce yellowing, but reduced KHN. DC, R p max and KHN were dependent on PD abs.