Air-abrasion and Er:YAG Parameters Influence Repair Durability of Bulkfill Composite

Objectives: The repair of failed resin composite can be clinically challenging, and the durability of the repaired restoration requires a strong bond. In this study, we aim to investigate the effect of surface treatment and Er:YAG laser settings on the repair bond strength of aged bulk-fill (BF) resin composite after thermocycling, using different repair materials.
Methods: Fifty standardized surface-polished composite-resin cylindrical specimens (2mm height X 10mm diameter) fabricated from Filtek Bulk-Fill Restoratives (BFR) composite-resin (3M ESPE) were aged by thermocycling (X5000 between 5°C and 55°C, with a 30 s dwell time in each bath). Specimens were divided into five groups according to the surface treatment: Er:YAG laser at 50mJ/20Hz/1W, Er:YAG laser at 150mJ/20Hz/3W, Er:YAG laser at 250mJ/20Hz/5W, air abrasion (A) or diamond bur as a control (C). Following treatment, Single Bond Universal Adhesive was applied and light-cured. Three standardized composite-resin cylinders (2mm x 2mm) were built on each treated surface, using either BFR, Filtek Bulk-Fill Flowable (BFF), or Filtek Z250 XT Nano-Hybrid composite (NH) and light-cured (n=10). Subsequently, the samples were further thermo-cycled (X5000), then subjected to shear bond strength (SBS) testing. Statistical analysis was done using two-way ANOVA and Bonferroni Post Hoc test (α=0.05).
Results: Specimens treated with air abrasion (NH;35.0±3.5, BFR;33.6±7.5, BFF;33.5±6.3 MPa) and 5W laser (NH;25.2±2.7, PFR;40.5±5.2, PFF;32.8±3.3 MPa) revealed significantly higher (p< 0.05) SBS than other tested groups; Bur (NH;24.1±11.8, BFR;25.7±4.2, BFF;21.2±6.3 MPa), 1W (NH;17.5±5.8, BFR;14.9±2.3, BFF;20.1±6.1 MPa), 3W (NH;23±6.4, BFR;20.9±5.7, BFF;28.9±9.2 MPa). Higher bond strengths (p<0.05) were recorded when the two BF materials were used for repair following 5W laser treatment.
Conclusions: SBS of the repaired aged BFR composite-resin is highly influenced by surface treatment. Air abrasion and 5 W laser power output can significantly increase the repair bond strength after thermocycling. The use of BF materials can enhance the repair bond strength of the aged BFR composite-resin.