Shelf-life Impact on Bond-strength and MMPs Expression of Universal Adhesives

Objectives: The aim of this study was to evaluate the immediate bonding ability expressed as microtensile bond strength (µTBS) and nanoleakage expression (NL) of a simplified universal adhesive system used in combination with dual-cure resin cement considering its expiry date (as-received or end of shelf-life). The endogenous enzymatic activity was investigated with in situ zymography.
Methods: Ten composite overlays were luted to deep coronal dentin surfaces with a simplified bonding system (iBond universal adhesive, used in the self-etch modality) in combination with a dual-cure resin cement (RelyX Ultimate; 20s of light-cure followed by 15 min of self-cure at 37°C). The bonding agent was used as-received by manufacturers or after 3 months of its expiry date. After 24h, each specimen was cut into microtensile sticks (1mm²) and stressed to failure under tension. The fracture pattern was evaluated with optical microscope. µTBS data were statistically analyzed with two-way ANOVA/Tukey’s test (p=0.05) including premature failures. Additional specimens (n=2) were processed for quantitative interfacial NL expression using ammoniacal silver nitrate. In situ zymography was performed to investigate MMPs activity within the hybrid layer (HL).
Results: The µTBS to dentin of the simplified bonding system significantly decreased after evaluation in the “end of shelf-life” condition (p<0.05). NL resulted in higher deposition of AgNO3 granules when the adhesive was used after the expiry date. In situ zymography assay revealed three times as much higher level of fluorescence when the bonding system was used at the end of shelf-life compared to the as-received adhesive.
Conclusions: Longer storage time, beyond the expiry limit, affect the performance of the universal adhesive tested. Furthermore, the higher endogenous enzymatic activity would portend for a shortened durability of the restoration.