Advanced biomechanics and stability of the resin-dentin complex via modular A- and B-type proanthocyanidins

This study explored the formation and sustainability of the resin-dentin complex optimized by four proanthocyanidins (PACs), modularly defined catechin oligomers with distinct single (B-type) or double (A-type) interflavanyl linkages (IFLs; AA, BB, AAA, BBB). Assessment of their biomimetic potency on the resin-dentin interface [adhesive, hybrid layer (HL), underlying dentin (UD)] involved nano-mechanical dynamic analyses, microtensile bond strength (μTBS), and interfacial micropermeability after 24 h and 6 months in simulated body fluids. The degree of conversion (DC) of PAC-incorporated dental resins was analyzed via ATR-FTIR spectroscopy. Bound and unbound water in dentin were measured using differential scanning calorimetry. Statistical analysis employed ANOVA and post-hoc tests (α = 0.05). A-type PACs increased HL nano-moduli (E'_HL = 15-17 GPa), and all PACs enhanced UD nano-moduli (E'_UD = 35-52 GPa) versus control (E'_HL = 10 GPa; E'_UD = 25 GPa). AA, BB, and BBB PACs increased damping capacity at HL, while reducing it at the UD (p < 0.001). A-type and BB PACs yielded greater bond strength than control. While nano-moduli in the BB group remained stable over 6 months, others declined, although trimers maintained higher E'_HL,UD than control (p < 0.001). While AA and BB groups sustained bond strength, AAA displayed higher μTBS over time. PACs did not adversely affect DC, whereas A-type PACs increased selectively. Hydric content remained stable post-PAC treatment, except with BB, which reduced total and unbound water. Collectively, PACs stabilized the adhesive interface and enhanced resin-collagen interactions. Notably, A-type PACs yielded more robust and durable interfaces than B-type PACs, with IFL and degree of polymerization modulating bioactive potency at the adhesive interfaces.