Long-term nano-dynamic mechanical analysis and micro-permeability of adhesive interface components using four AB-type proanthocyanidin neutral primers

Objective: This study investigated the long-term biomodulatory roles of trimeric and tetrameric AB-type PAC-DESIGNER primers on the viscoelastic properties and stability of dentin-resin components over 1-year aging. Methods: PAC-DESIGNER primers were prepared from Pinus massoniana (PM) and Cinnamomum verum (CV) extracts and designed to enrich trimeric (PM-AB, CV-AB) and tetrameric (PM-ABA, CV-ABB) proanthocyanidins. Adhesive interfaces were prepared on dentin surfaces under an etch-and-rinse bonding protocol. Specimens were sectioned and either immediately processed or stored in simulated body fluid for one year. Unprimed adhesive restoration served as control. Nano-mechanical properties (complex modulus – E* and damping capacity – Tan δ) of adhesive layer, hybrid layer, and underlying dentin were assessed using triboindentation. Interfacial micro-permeability was evaluated under a fluorescent microscope. Data were analyzed using ANOVA and post-hoc tests (α = 0.05). Results: No significant differences in E* were found among adhesive layers of PAC-DESIGNER groups vs. control at immediate and 6-month timepoints (p ≥ 0.05). After 1-year aging, E* was higher for CV-ABB and PM-AB adhesive layers than the control (p < 0.05). AB-type PAC-DESIGNER primers increased the viscoelastic properties of the hybrid layer and underlying dentin, with trimeric compounds performing better at all timepoints (p < 0.05). Biomodulation did not affect the nature and viscoelastic behavior of the different layers: at both the hybrid layer and underlying dentin. PAC-DESIGNER primers reduced rhodamine infiltration compared to the control group (p < 0.05). Conclusions: AB-type PAC-DESIGNER primers enhanced viscoelastic properties and stability over time for both the hybrid layer and the underlying dentin. Trimeric proanthocyanidins exhibited superior performance compared to tetrameric, which can be attributed to their distinct molecular configuration and overall shape. Clinical Significance: Plant-derived biomodulator primers have the potential to stabilize dentin-resin interfaces by increasing the mechanical properties and sealing of the hybrid layer and underlying dentin.