Ion-releasing Materials Applied Using Universal Adhesives: Effects of Short/Long-term Ageing

Objectives: The study aimed at evaluating the microtensile bond strength (MTBS) and fractographic features of resin-dentin bonded specimens created using modern universal adhesives in combination with RMGIC-based materials after short-term load-cycle or prolonged aging (load-cycle + 8 months storage in artificial saliva).
Methods: Dentin specimens were prepared and bonded in etch-and-rinse (ER) or in self-etch (SE) mode using two universal adhesives (FTB: Futurabond M+, VOCO; SCU: Scotchbond Universal, 3M-ESPE) as per manufacturer’s instructions. Composite build-ups were made using a nano-filled composite or resin-modified glass ionomer cement (Ionolux VOCO), or a GIC-based composite (ACTIVA, Pulpdent). The first group was cut into matchsticks (0.9 mm²) and tested immediately for MTBS. The second group was submitted to load cycling (350,000 cycles; 3 Hz; 70 N) and then tested for MTBS. The third group was first submitted to 350,000 load cycles and then immersed for 8 months storage in artificial saliva (AS); these were finally tested for MTBS. The results were analyzed statistically using three-way ANOVA and Fisher's LSD post hoc test (p <.05). Fractographic analysis was performed through stereomicroscope and FE-SEM.
Results: FTB showed no significant drop in bond strength after ageing protocols, Regardless the restorative material used. the use of both GIC-based materials, prevented the bond strength reduction in SCU after short- and long-term aging protocols. The SEM analysis showed severe degradation in specimens created with composite and SCU applied in ER mode; this was less evident when GIC-based materials were used to restore the SCU-bonded specimens.
Conclusions: Dentin-bond longevity depended on the adhesive type rather than the mode of application (ER vs. SE) or the restorative material employed for the restoration. However, the use of GIC-based materials may maintain the bonding performance of simplified universal adhesives over time, especially when these are applied in ER mode.