Lanthanum Ion-Engineered Hybrid Layer Improves Dentin Bonding

The retreatment of failed adhesive restorations consumes more than 60% of clinical resources. Patient factors-such as caries risk, oral hygiene, diet, and occlusal stress-contribute to failure primarily. However, the contribution of the degradation of the adhesive-dentin interface to the failure cannot be ignored and involves 3 interrelated challenges: (1) highly hydrated demineralized dentin matrix (DDM) hindering adhesive infiltration, particularly in the partially demineralized zone; (2) residual hydroxyapatite (HAP) prone to dissolution; and (3) degradation of unprotected collagen by acid-activated matrix metalloproteinases (MMPs) and colonized microbes. To synchronously address all 3 failure mechanisms, a breakthrough strategy was developed based on lanthanum ion (La³⁺) pretreatment. Morphological changes were observed by field emission scanning electron microscopy and transmission electron microscopy; chemical and crystal properties were analyzed by selected area electron diffraction, energy-dispersive X-ray spectroscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy; microhardness and surface potential were detected by atomic force microscopy; water content and type were characterized by attenuated total reflection-Fourier transform-infrared spectroscopy; enzyme inhibition was assayed by in situ zymography; adhesive infiltration was traced by Nile red; bonding effectiveness was mainly measured through microtensile bonding strength test and nanoleakage; and antibacterial activity testing was carried out on Streptococcus mutans. After a 20-s treatment of the DDM with a drop of LaCl₃ solution before applying the adhesive, (1) noncollagenous protein aggregation induced DDM dehydration, in turn enhancing adhesive infiltration; (2) MMP was inhibited (almost 100% activity reduction) and S. mutans was suppressed; and (3) atomic-scale HAP remodeling was performed via Ca₈La₂(PO₄)₆O₂ crystallization, increasing thermodynamic stability. This trimodal intervention creates a defect-minimized hybrid layer with enzymatic resistance, bacteria inhibition, and structurally reinforced base, demonstrating 77.30% higher bonding strength after 10,000 thermocycles versus controls. The protocol's chairside compatibility (20 s of chair time) and biosafety validation establish La³⁺-assisted bonding as a clinically translatable strategy to disrupt the restoration failure cycle, offering transformative potential for sustainable dental care.