Objective: This study aimed to assess the hydrolytic stability of the adhesive interface between repaired bulk-fill and bulk-fill resin composites after 12 months of water storage.

Materials and methods: Bulk-fill resin composite specimens were bonded to smooth substrate surfaces using three different primer/bonding systems. A total of 35 specimens were prepared for shear bond strength (SBS) testing, and 30 specimens for micro-tensile bond strength (μTBS) testing. The specimens were aged in water at 37°C for 12 months, after which SBS and μTBS were evaluated.

Results: The mean SBS ranged from 6.0 to 14.9 MPa, with the highest values observed for the Ceramic primer. The mean μTBS ranged from 0 to 7.8 MPa, with the Composite primer yielding the highest values. Both primers outperformed the three-step etch-and-rinse adhesive in terms of bond strength.

Conclusions: The Ceramic primer (containing silane) and the Composite primer exhibited superior adhesive performance compared to the three-step etch-and-rinse adhesive, demonstrating better long-term bond stability.

Clinical relevance: The findings suggest that using Ceramic or Composite primers can enhance the durability of repaired bulk-fill composite restorations, improving adhesive stability and long-term clinical outcomes.