Mineralization/Nano-deposition Boosts Adhesive Infiltration via Dehydration

Preadhesion mineralization and in situ nano-deposition improving dentin bonding durability are currently explained by divergent paradigms: the former is attributed to collagen strengthening and protease fossilization, while the latter is known for the release of interface-confined water. This study challenges this dichotomy by hypothesizing that preadhesion mineralization fundamentally acts as a dehydration strategy. Two bonding strategies were formulated: a polyacrylic acid-stabilized amorphous calcium fluoride (PAA-ACF) preadhesion mineralization and in situ ACF nano-deposition. Cryo-transmission electron microscopy (TEM) revealed collagen binding by ACF nanoparticles within 30 s, whereas scanning electron microscopy, X-ray diffraction, and TEM showed that PAA‑ACF-mediated intrafibrillar mineralization on etched dentin began within 30 min and reached completion by 3 h. The PAA-ACF 3-h mineralization group showed approximately twice the surface roughness and elastic modulus of the phosphoric acid (PA) and ACF 30-s deposition groups, as measured by atomic force microscopy, whereas its gelatinase activity (assessed by zymography) was substantially lower, only about one-fifth and one-third of the levels in the PA and ACF 30-s groups, respectively. Fourier transform infrared spectroscopy, water absorption, and thermogravimetric analysis confirmed that both strategies effectively released the interface-confined water. Notably, both the nano-deposition and mineralization groups displayed similarly low proteolytic activity in resin-dentin interfaces. After 30,000 thermal cycles, the micro-tensile bond strength of the 3-h group was statistically comparable to that of the ACF 30-s group and exceeded that of conventional PA wet-bonding. Pearson correlation analyses revealed that bonding strength correlated not with mechanical properties or protease activity of preadhered dentin but with the extent of dehydration, which facilitated infiltration of the hydrophobic adhesive monomer (Bis-GMA), as validated by Nile red tracing and micro-Raman analysis. In summary, both strategies enhance adhesive infiltration by releasing the interface-confined water, forming a defect-low hybrid layer. This finding unifies the understanding of dentin bond durability improvement under a common dehydration-based mechanism.