Influence of Light-Curing Parameters on the Bond Strength of Bulk-Fill Repaired Microhybrid Resin Composite

This study evaluated the influence of photoactivation parameters, specifically radiant exposure and curing distance, on the microtensile bond strength (μTBS) of a microhybrid resin composite repaired with a bulk-fill composite. Seventy-two conventional resin composite blocks were prepared and thermocycled (10,000 cycles). Three light-curing modes were evaluated based on their clinical parameters: Standard (1000 mW/cm2, 20s), High Power (1400 mW/cm2, 8s), and Xtra Power (3200 mW/cm2, 6s). Specimen surfaces were ground with a diamond bur, etched with 35% phosphoric acid, and treated with a 2-step etch-and-rinse adhesive system (Adper Single Bond 2) before repairs were made with a bulk-fill composite. Specimens (n=12 per group) were divided based on the three irradiances and two curing distances (0 and 2 mm). After 14 days of water storage, μTBS was tested. Data were analyzed using two-way ANOVA (α=0.05). Curing distance significantly influenced μTBS, with higher values at 0 mm (p<0.05). The combination of Xtra Power (3200 mW/cm2) and increased distance (2 mm) led to numerous pre-test failures and a significant reduction in bond strength. Curing distance and radiant exposure are critical factors for bulk-fill composite repair bond strength. High irradiance combined with increased distance negatively affects repair quality, emphasizing the importance of proper photoactivation technique.