Effect of Different Surface Treatment Protocols on Shear Bond Strength of Bulk-fill Resin Composite: an SEM Evaluation

Abstract

Purpose To evaluate the repair bond strength of aged bulk-fill resin composites using various surface treatment protocols and analyze the composite–composite interface via scanning electron microscopy (SEM). Materials and Methods One-hundred fifty disk-shaped specimens (4 mm height × 5 mm diameter) were prepared from three bulk-fill composites. After thermocycling (10,000 cycles, 5°C–55°C), specimens were assigned to five groups: (1) control (no treatment); (2) Universal adhesive (UA); (3) 37% phosphoric acid + UA; (4) silane + UA; and (5) CoJet + Silane + UA. Filtek Bulk-Fill Flowable was applied as the repair composite. After 24-h storage, shear bond strength (SBS) was measured, and one specimen per group was examined under SEM. Results Two-way ANOVA showed statistically significant effects of both surface treatment and composite type on SBS (p < 0.05). CoJet + silane + UA produced the highest SBS values for all composites, whereas the untreated control produced the lowest values. No statistically significant difference was observed between UA and phosphoric acid + UA (p > 0.05), while silane + UA resulted in statistically significantly higher SBS values than both protocols. Material-dependent differences were observed in some treatment groups; however, no statistically significant differences among the three composites were detected following phosphoric acid + UA or CoJet + silane + UA treatment. Conclusion Surface treatment statistically significantly improved the repair bond strength of aged bulk-fill composites. The combination of CoJet, silane, and universal adhesive provided the most effective bond enhancement.