Introduction: Bulk-Fill flowable composites are low viscosity materials with reduced percentage of inorganic fillers, leading to more shrinkage but with minimal stress contraction, maintaining the marginal seal of the restoration.
Objectives: To evaluate the polymerization shrinkage and marginal integrity of two flowable bulk-fill composites cured by different light curing modes at different curing distances.
Materials and methods: Two types of flowable bulk-fill composites (Tetric EvoFlow, CLEARFIL AP-X Flow) were tested. For shrinkage test, 30 cylindrical specimens (5 mm diameter x 2 mm thickness) were prepared from each type of composite. For marginal integrity evaluation, 30 class II occluso-mesial cavities (3 mm width x 2.5 mm depth at the occlusal box and 3 mm width x 1.5 mm depth x 1 mm occluso-cervical height of the proximal box) were prepared and restored from each type of composite. The composites were cured using three LED light curing modes for 10 seconds (high mode at 1200 mW/cm², low mode at 650 mW/cm²andsoft-start mode at 650 up to 1200 mW/cm²  for 5 seconds then at 1200 mW/cm² for 5 seconds) at two curing distances (0 mm, 3 mm). Strain gauge was used to measure the shrinkage. Stereomicroscope was used to evaluate the microleakage and scanning electron microscope was used to measure the gap width. Data was analyzed using Mann-Whitney U, Kruskal-Wallis and Pearson's Chi square tests.
Results: Tetric EvoFlow showed less marginal gap values than CLEARFIL AP-X Flow. Soft-start and high modes showed less microleakage and gap than low mode.0 mm distance showed less shrinkage and microleakage in soft-start and high modes than low mode. 3 mm distance showed less gap proximally in soft-start and low modes than high mode.
Conclusions: Different LED light curing modes and distances showed comparable results of shrinkage, microleakage and gap values for both composites tested.