Fatigue behavior of the resin-resin bond of partially replaced resin-based composite restorations

Purposes (1) To evaluate different pre-treatment modes for partial resin-based composite repair using a shear bond strength fatigue design on aged specimens, and (2) to investigate the effect of these pre-treatments on aged and partially replaced Class II resin-based composite restorations. Materials and Methods: (Study 1) 150 composite discs (Tetric Ceram) were light-cured, secondary cured, and stored in water for 365 days. The specimens were randomly assigned to five pretreatment groups (n=30): (1) Roughening with a finishing diamond bur + dentin bonding system (DBS, Syntac Classic), (2) Roughening with a silicon carbide bur + DBS, (3) Roughening with a silicon carbide bur + DBS + Tetric Flow, (4) silica-coating (CoJet) + DBS, and (5) silica-coating + dentin bonding agent + Tetric Flow. The disks were restored with fresh repair composite cylinders and after 24-hour water storage, initial bond strengths (n=10) and fatigue bond strengths (n=20; 5,000 cycles in shear mode) were evaluated and fracture modes determined under a SEM. (Study 2): 40 Class II restorations (EBS Multi/Pertac II) were placed in extracted human third molars. The specimens were stored for 365 days and then replaced partially by removing the proximal box and leaving the occlusal part. The partial repairs (Pertac 11) were placed after identical pre-treatment modes A-E (n=8). After thermomechanical loading (100,000 x 50 N, simultaneously x2,500 at 5degreesC/55degreesC), marginal quality between old and fresh composite was evaluated by SEM at x200 magnification and dye penetration was observed by light microscopy under x50 magnification. Results: Initial repair bond strengths were significantly higher for the groups with additional application of flowable composite compared to composite only (P< 0.05; Mann Whitney U test). Diamond finishing revealed the lowest bond strengths. Fatigue bond strengths exhibited the worst results for Group 1 as well, but were similar for Groups 2-5. In the Class II partial repair simulation, Groups 3 and 5 with additional flowable lining exhibited significantly better marginal quality and significantly lower leakage, whereas the other groups revealed up to 100% separation between aged and freshly applied composite. (Am J Dent 2003; 16:17-22).