Calcium stoichiometry governs depth-oriented remineralization by fluoride-calcium-phosphate complexes in enamel and dentin.

OBJECTIVES: This study aimed to evaluate the effects of fluoride-calcium-phosphate (FCP) complexes with varying calcium concentrations on demineralization inhibition in sound enamel and dentin, and on mineral recovery and lesion depth in demineralized tissues. METHODS: Enamel and dentin blocks (5 × 3 × 2 mm³; n = 120 each) were prepared from bovine teeth. Specimens were assigned to sound or demineralized conditions and treated with Control, FCP0, FCP1, or FCP2 for 10 min, followed by 2 weeks of pH cycling. Demineralization inhibition and mineral recovery were assessed using swept-source optical coherence tomography (SS-OCT) and micro-computed tomography (micro-CT). Chemical changes were analyzed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and crystallographic characteristics were evaluated using wide-angle X-ray scattering (WAXS). RESULTS: FCP2 showed the strongest inhibition of demineralization in sound enamel and dentin, with minimal structural and mineral changes. In demineralized specimens, all FCP-treated groups enhanced mineral recovery compared with the Control. Among them, FCP2 generally showed the highest mineral recovery and the greatest reduction in lesion depth, particularly in dentin. FTIR analysis indicated compositional trends in enamel and dentin, with more pronounced patterns in enamel. WAXS indicated predominantly amorphous structures, with weak CaF₂-associated reflections detected only in FCP1 and FCP2. SIGNIFICANCE: Calcium-rich FCP complexes enhance both inhibition of demineralization and promotion of mineral recovery, demonstrating improved control of lesion progression compared with conventional fluoride conditions. These findings suggest that FCP-Complex represents a promising strategy for improving fluoride-based caries management through enhanced mineral dynamics and depth-oriented remineralization.