Evaluation of Surface Treatment Protocols on Aged Repaired Composite Restorations

Objectives: To evaluate the effect of several surface treatment protocols and thermal cycling aging over the shear bond strength (SBS) of different resin composites.
Methods: Resin composite blocks of four different composites (Filtek Z350XT (Z350)–3M ESPE®, Empress Direct (ED)–Ivoclar Vivadent®, Spectra smart (SS)–Dentsply Sirona® and Forma (FO)–Ultradent®) were made (n=100/each; 400 resin blocks total). Blocks were evaluated immediate (24h) and aged (5000 thermal cycles) and then randomly assigned to different repair surface treatments (10 groups in total, n=10/each resin composite brand). Repair composites were the same used for the resin block. After 24h of repair composite application, specimens were tested for SBS testing and type of fracture was observed with a loupe at 2.5x magnification. One sample per group was observed through scanning electronic microscopy (SEM) images. Data was analyzed by Anova three-way and Tukey post-hoc tests (p=.05).
Results: The highest SBS value (20,7 MPa±1,31) were obtained by Z350 within the repair protocol with dry sandblast (DS) + phosforic acid (PA) + universal adhesive (UA), statistically similar than all other resins within the same group (p>.05), and the lowest SBS (10,48 MPa±1,09) was shown by FO with PA+UA protocol, statistically similar than all other resins within the same protocol (p>.05), both performed in aged resin composites. For all four resin composites, the highest SBS where shown in groups who included any type of sandblast in their step-by-step repair protocol.
Conclusions: For most of the interventions, there were no significant differences between types of resin composites. Moreover, thermalcycling aging showed to significantly decrease the SBS when compared to control groups. Finally, the use of mechanical surface treatments is essential to achieve an effective adhesion in repair of composite resins, and the best surface treatment protocols where those who used any type of sandblasting.