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 (α) as a way to estimate the CLD. The results were analyzed by one-way ANOVA and Tukey'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 α. The mixture CQ/PPD produced statistically lower R_p^max 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.