Influence of Different Adhesives and Surface Treatments on Shear and Tensile Bond Strength and Microleakage with Micro-CT of Repaired Bulk-Fill Composites

The repair of defective composite restorations, particularly bulk-fill composites, offers a conservative alternative to complete replacement. However, establishing durable adhesion between aged and fresh composites remains a clinical challenge due to the altered surface properties of aged materials. This in vitro study investigated the effects of different surface treatment protocols (no treatment, diamond bur roughening, and air abrasion) and adhesive systems (G-Premio Bond, Clearfil SE Bond, and Adper Single Bond 2) on the shear bond strength (µSBS), tensile bond strength (µTBS), and microleakage of repaired bulk-fill composites. Results demonstrated that both surface treatment and adhesive type significantly affected bond strength (<i>p</i> < 0.05). Mechanical surface treatments, particularly diamond bur roughening and air abrasion, enhanced µSBS and µTBS compared to untreated controls. The highest µSBS and µTBS values were observed with diamond bur treatment combined with Adper Single Bond 2, reaching mean values of 25.8 ± 2.1 MPa and 28.3 ± 1.8 MPa, respectively. Air abrasion with Clearfil SE Bond also significantly increased bond strengths (µSBS: 22.1 ± 2.0 MPa; µTBS: 23.5 ± 1.7 MPa) relative to no treatment (<i>p</i> < 0.05). Micro-computed tomography analysis revealed that Clearfil SE Bond following diamond bur roughening resulted in the lowest microleakage scores, with a mean leakage volume of 0.12 ± 0.04 µm. These findings underscore the importance of mechanical surface conditioning and appropriate adhesive selection to enhance both bond strength and sealing efficacy in composite repair procedures.