Purpose: To evaluate the 6-and 12-month performance of microrepairs of marginal occlusal microdefects of resin composite restorations in a group of patients with high caries risk. Materials and Methods: Thirty-five patients with at least three resin composite restorations with marginal occlusal defects were randomly distributed into three treatment groups: (1) sealed with flowable resin composite; (2) sealed with resin-based sealant; or (3) control. Restorations in all groups were assessed using World Dental Federation (FDI) criteria at three time points: baseline, and at 6 and 12 months after sealing. Results: After 1 year, 32 patients were examined. Of all the repaired restorations, those of the flowable resin composite (RC) group maintained an FDI value of 1 for marginal occlusal adaptation for 81.3% of the restorations at 6 and 78.1% at 12 months. The resin-based sealant group kept a value of 1 for the same parameter on 65.6% of restorations at 6 and 50% at 12 months with a statistically significant difference (p= 0.024) between the two time periods. There was a statistically significant difference between the two groups at the 12-month comparison (p = 0.015). Conclusions: Occlusal RC restorations that were sealed using either a resin-based sealant or a nanofilled flowable RC benefited from improved clinical status after 12 months. Use of the latter presented the better clinical performance of the two by providing a higher rate of total retention of sealing materials. Keywords: flowable resin composite, nanofilled, repair, sealing, universal adhesives