In situ Synthesis of Amorphous Fluorinated Calcium Phosphate Nanoparticles via a Dual-Component Hydrogel for Biomimetic Tooth Remineralization

Abstract

Objective To report the in situ synthesis of amorphous fluorinated calcium phosphate (AFCP) nanoparticles within a dual-component hydrogel and evaluate their efficacy for enamel remineralization and dentinal tubules (DTs) occlusion. Materials and Methods The AFCP hydrogel was constructed using hydroxypropyl methylcellulose (HPMC) and carboxymethyl chitosan (CMC) to stabilize calcium, phosphate, and fluoride ions in a metastable amorphous state. Physicochemical characterization was performed by FTIR, XRD, TEM, and SEM-EDX. Biocompatibility was assessed via CCK-8 assays and oral mucosal irritation test. Demineralized enamel and dentin specimens (n=8) were treated with deionized water, fluoride (NaF, 2000 ppm F), 10% CPP-ACP with 900 ppm F (GC Tooth Mousse Plus, Japan), or AFCP hydrogel, and immersed in artificial saliva for 7 days. Remineralization was evaluated by SEM, XRD, and nanoindentation, followed by in vivo validation in a rabbit model. Results The hydrogel generated AFCP nanoparticles (30–80 nm) that remained amorphous in artificial saliva for over 2 hours before crystallizing into hydroxyapatite. The hydrogel exhibited negligible cytotoxicity and no oral mucosal irritation. After 7 days, the AFCP hydrogel induced dense mineral deposition that completely occluded exposed DTs and formed a ~32 µm remineralized layer on acid-etched enamel, substantially outperforming fluoride and CPP-ACP + NaF. XRD confirmed the newly formed mineral as hydroxyapatite-like. Treatment with the AFCP hydrogel restored the mechanical properties of enamel and dentin to near-physiological levels, achieving the greatest recovery among the four groups (P < 0.05). In vivo results further validated its remineralization and tubule-occluding efficacy. Conclusion The AFCP hydrogel functions as an exogenous mineral reservoir, enabling sustained ion release or direct transformation into hydroxyapatite for in situ enamel remineralization and DTs occlusion. This non-invasive strategy offers a promising therapeutic approach for early caries and dentin hypersensitivity.