Alternative photoinitiator system reduces the rate of stress development without compromising the final properties of the dental composite

Objectives. Stress development during the polymerization process continues to be a major factor that limits predictability and longevity of resin composite restorations. This study evaluated the effect of the photoinitiator type on the maximum rate of polymerization (R-p(max)), stress development (final stress and maximum rate, R-stress(max)), degree of conversion (DC) and cross-link density (CLD) of materials containing camphorquinone (CQ), phenylpropanedione (PPD) or CQ/PPD. Materials and methods. R-p(max) was evaluated via differential scanning calorimetry (DSC). Contraction force measurement was assessed with a single cantilever device for 5 min. The samples were subsequently tested by infrared spectroscopy (FTIR) to evaluate the DC. After, samples were soaked in ethanol to evaluate the swelling coefficient (alpha) as a way to estimate the CLD. The results were analyzed by one-way ANOVA and Tlukey's test (p = 0.05). Results. CQ showed the highest R-p(max) and R-stress(max). PPD produced the lowest DC and the highest alpha. The mixture CQ/PPD produced statistically lower Rpmax and R-stress(max) than CQ alone, but similar DC and CLD. Conclusion. CQ/PPD reduced the R-p(max) and R-stress(max), without a reduction in DC and CLD. Therefore, the use of alternative photoinitiator systems could be a promising way to reduce the stress developed during the composite's polymerization without affecting the final properties. (C) 2008 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.