Clinically Oriented Oral Environment-Triggered Underwater Adhesives for Root Caries Treatment through Dentinal Tubule Occlusion and Remineralization

The application of silk fibroin (SF) hydrogels is often limited by their brittleness; on the other hand, increasing ductility can lead to insufficient strength of the hydrogel. These drawbacks make it difficult to apply to treat root surface caries, which are continuously exudated by crevicular fluid and have special locations and shapes. Herein, we design an underwater adhesive hydrogel with a fluid–solid spontaneous transition triggered by water for root caries treatment. Guanidine hydrochloride (GH), amorphous calcium phosphate nanoparticles (ACP), and tannic acid (TA) are applied to coassemble with SF to form an underwater adhesive hydrogel (STAG). GH as a hydrogen bond dissociator can break the hydrogen bonds between SF and TA and rapidly diffuse in a water environment, thus providing the system with high fluidity and regelation ability. Ca2+ of ACP can chelate with TA to enhance the cohesion of the hydrogel. Hydrogel containing ACP has stronger adhesion strength in lap-shear and tensile tests than hydrogel without ACP and also exhibits better properties in rheological tests. Even if stored in freeze-dried powder form for 90 days, the STAG fluid can be smoothly injected from the needle with only 0.8 N, completely filling the defective area of root caries and solidifying in situ. The formed restorative material can effectively promote tooth remineralization and seal the dentin tubules, which provides a feasible pathway for the treatment of root caries.