Effect of Aqueous Storage on Original and Repair Bond Strength and Residual Monomer Release of Fiberreinforced Composites

Purpose: To evaluate the effects of aqueous storage on shear bond strength (SBS) and monomer release of fiberreinforced composites (FRCs). Materials and Methods: Four unidirectional FRCs were tested, including one semi-interpenetrating polymer network (IPN) (ES, everStick) and three cross-linked polymer (CLP) FRCs (GT, GrandTec; TF, TenderFiber; DP, Dentapreg). The SBS of samples of original resin to fresh FRC with an intact oxygen inhibition layer (n = 30/group) and repair resin to FRC after surface treatment (n = 30/group) was evaluated after 6 and 12 months of storage in artificial saliva. Monomer release of polymerized resin-coated and uncoated FRCs was detected by high-performance liquid chromatography after immersion for 1 h, 1 day, and 7 days. Results: After 6 months, a significant decrease in SBS was seen with ES-repair (p 0.0001). After 12 months, significant decreases were seen with ES-original (p 0.0001), ES-repair (p 0.0001), and TF-repair (p = 0.0003). A significant reduction was also found for GT-original (p = 0.0254) and GT-repair (p = 0.0176). At 6 and 12 months, GT showed the highest SBS values, with DP-repair being statistically similar to GT at 12 months. For UDMA and bis- GMA, the greatest amounts of release were seen in uncoated specimens, followed by flowable resin-coated and viscous resin-coated specimens. Conclusion: Matrix composition, interfacial bonding, and resin coverage seem to account for differences in the aging behavior of FRCs. The semi-IPN material is likely to suffer most from the challenging oral conditions. CLP FRCs might be more stable over the long term. Coverage of FRCs with viscous resin is highly recommended to reduce residual monomer release. Keywords: fiber-reinforced composites, aging, artificial saliva, aqueous solvent, shear bond strength, residual monomer release