Role of interface-confined water in the redistribution effect of demineralized dentin matrix on adhesive monomers.

OBJECTIVE

To elucidate how the interplay between interface-confined water and the demineralized dentin matrix (DDM) determines adhesive monomer infiltration and bonding durability.

METHODS

Interface-confined water was modulated via amorphous calcium phosphate (ACP) deposition and copper ion (Cu²⁺) coordination. Effects on DDM hydration, porous network capacity, surface polarity, electronegativity, and dielectric behavior were analyzed. Rehydration kinetics and dielectric spectroscopy were used to track water dynamics. A poly(acrylic acid) (PAA)-grafted collagen model verified intrinsic matrix behavior. Reversible ACP-ethylenediaminetetraacetic acid (EDTA) provided causal evidence linking interface-confined water displacement to monomer infiltration and bonding effectiveness.

RESULTS

Interface-confined water structurally integrated in the DDM amplified its intrinsic fractionation effect, limiting uniform adhesive infiltration. Dehydration induced fibrillar contraction, matrix rearrangement, and reduced surface polarity, enhancing compatibility with hydrophobic monomers such as bisphenol A glycerolate dimethacrylate (BisGMA). Rehydration restored matrix electronegativity and dielectric response. The biomimetic model confirmed that the mechanism is intrinsic to charged hierarchical networks. EDTA cycling demonstrated that water displacement improved monomer infiltration and bond strength, while water restoration reversed these gains.

CONCLUSION

The DDM provides the substrate-level basis for adhesive fractionation, while interface-confined water acts as its structurally integrated amplifier. Modulating the DDM to regulate its interface-confined water therefore provides a mechanistic route to enhance adhesive infiltration and bonding durability. This framework points to a water-centric to a matrix-centric shift in dentin bonding, where the substrate's hydrated charged architecture actively determines monomer partitioning and bonding durability.