Lanthanum Ion–Engineered Hybrid Layer Improves Dentin Bonding

Abstract

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.