Effect of Curing Techniques on Microleakage and Microhardness of Bulk-Fill and Conventional Resin-Based Composites: An In Vitro Study

Adequate polymerization of resin-based composites is essential for marginal sealing and mechanical performance. This study evaluated the effects of different light-curing protocols on gingival microleakage and microhardness of a high-viscosity bulk-fill composite, Filtek™ One Bulk Fill Restorative (3M ESPE; AUDMA, AFM, UDMA, 1,12-dodecane-DMA; silica/zirconia fillers, 76.5 wt%, 58.4 vol%) and conventional nanohybrid composite, Filtek™ Z250 XT Universal Restorative (3M ESPE; Bis-EMA, UDMA; zirconia/silica fillers, 82 wt%, 68 vol%). Forty-eight extracted human second premolars and 48 cylindrical specimens were used for microleakage and Vickers microhardness testing, respectively. Specimens were cured using an O-Star LED unit in turbo mode (2700–3000 mW/cm2, 3 s) or soft-start mode (0–1200 mW/cm2, 20 s) at 2 mm and 5 mm distances. Data were analyzed using Kruskal–Wallis and Dunn’s tests (p < 0.05). Significant differences were found among groups. Soft-start curing at 2 mm produced the lowest microleakage, whereas turbo curing at 5 mm produced the highest. The conventional composite exhibited higher top and bottom microhardness values. Bottom-to-top hardness ratios were below 80% in most groups, except for the conventional composite cured with soft-start mode. Based on our findings, soft-start curing at short distances provides favorable outcomes, while turbo curing at 5 mm is not recommended.