Repair Bond Strength of Aged Bulk-Fill Composites: Influence of Different Primers and Direction of Debonding Stress.

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. 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. 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. 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. 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.