Synchrotron evidence reveals ion-mediated self-repair of mineralized tissue in silver-fluoride–ionomer reinforced carious dentin

Conventional caries management relies on mechanical excavation, which inevitably removes potentially remineralizable tissue. This study demonstrates that caries-affected dentin can regain structural and mechanical integrity without tissue removal through ion-mediated self-repair. Extracted human teeth with natural root caries were treated with silver diamine fluoride (S), glass ionomer cement (G), or their combination (SG), and stored in artificial saliva for up to 6 months. Specimens were evaluated using micro-computed tomography (micro-CT), synchrotron-based wide-angle X-ray scattering (WAXS), and nanoindentation. Micro-CT revealed a time-dependent mineral gain in the SG group, while WAXS revealed fluorapatite-like and silver-substituted hydroxyapatite (HAp) phases, along with distinctive correlation peaks indicating ionic cross-linking at the dentin–GIC interface. Nanoindentation confirmed significant mechanical reinforcement after 6 months, with the highest nanohardness in the SG group. The results suggest that silver and fluoride ions from SDF were stabilized and gradually migrated through the GIC layer, promoting lattice reorganization and interfacial reinforcement within the underlying dentin. These findings provide mechanistic evidence that SDF beneath GIC facilitates self-repair of demineralized dentin through sustained ionic migration and structural reorganization, combining antimicrobial action with ion-mediated structural reinforcement. This ion-mediated self-repair concept supports a non-cutting minimally invasive strategy that preserves carious dentin and enhances substrate resilience.