Effect of Photoinitiator Systems and Light‐Curing Units on the Microhardness and Degree of Conversion of Resin Composites

ABSTRACT This study investigated the influence of light‐curing unit (LCU) choice on the polymerization of commercial composite resins with varying photoinitiator ratios and types, as reflected by their mechanical and physical properties, with a focus on surface hardness and degree of conversion. Four commercially available composite resins (Solitare 2, Filtek Z250, Tetric EvoCeram Bleach, and Tetric EvoCeram Bulk Fill) with distinct photoinitiators were polymerized using four LCUs: one second‐generation LED (Elipar S10), two third‐generation LED (Bluephase 20i and Valo), and one halogen lamp (Hilux). The data were analyzed using SPSS. The upper surfaces exhibited higher hardness values than the lower surfaces across all composite resins, with Tetric EvoCeram Bleach exhibiting the highest degree of conversion. Thus, the choice of photoinitiator and LCU significantly impacts polymerization and clinical restorative outcomes. This study highlights the limitations of third‐generation LED LCUs and other photoinitiators, offering insights for selecting materials and methods to enhance restoration durability. Further research should explore in vivo conditions and additional clinical scenarios to validate these findings.