The Effect of Bulk-Fill Composites on Microleakage and Marginal Integrity

Bulk-fill resin composites were developed to address the limitations of conventional incremental layering techniques by enabling placement of thicker increments (up to 4–5 mm) with adequate depth of cure and reduced clinical time. One of the primary clinical concerns with resin composites is the development of polymerization shrinkage stress, which can compromise marginal integrity and increase the risk of microleakage. Microleakage contributes to secondary caries, marginal staining, and postoperative sensitivity, thereby reducing the longevity of restorations. This review synthesizes evidence from in vitro studies, micro-computed tomography (micro-CT) analyses, and randomized controlled clinical trials to evaluate the effect of bulk-fill composites on microleakage and marginal adaptation. Recent investigations (2024–2025) provide important insights into the performance of contemporary bulk-fill systems, including pre-heating techniques, dual-cure materials, and their clinical performance after two years. Overall, evidence suggests that bulk-fill composites demonstrate comparable or superior performance to incremental composites in terms of microleakage and marginal integrity, though outcomes are highly dependent on material formulation, curing method, and operator technique. Long-term studies remain necessary to validate their durability and optimize restorative protocols.