Introduction
Dentin hypersensitivity affects 15–30% of adults due to exposed dentinal tubules reacting to thermal or chemical stimuli. Conventional SnF₂-based treatments offer short-term relief but suffer due to the chemical instability of Sn²⁺ ions in the oral environment, poor taste, and limited integration with tooth structures. Hydroxyapatite (HAp), the primary mineral of enamel and dentin, provides a biocompatible and bioinspired scaffold for ion substitution. Incorporating Sn²⁺ into HAp could combine remineralization with long-lasting desensitization. However, Sn²⁺ is notoriously unstable—it oxidizes easily and hydrolyzes in aqueous environments. This study addresses the challenge of stabilizing Sn²⁺ during synthesis to ensure its incorporation into the HAp lattice, enhancing structural similarity to native enamel.
Methods
Sn-substituted HAp (Ca₉Sn(PO₄)₆(OH)₂) was synthesized via co-precipitation using Ca(NO₃)₂•4H₂O, SnCl₂, and (NH₄)₂HPO₄. Two solvent systems for SnCl₂ were compared: ethanol (low polarity, limits Sn²⁺ hydrolysis and oxidation) and 0.01M HCl (aqueous, stabilizes Sn²⁺ via acidification). Precipitation was induced at pH 7 using NaOH, followed by annealing at 500–900°C. Structural properties were analyzed by X-ray diffraction (XRD).
Results
Ethanol-based synthesis yielded sharper XRD peaks (e.g., intensity 179 vs. 125), indicating higher crystallinity and reduced structural defects. Peak shifts confirmed Sn incorporation: rightward shifts (e.g., 31.7° → 31.9°) suggested Sn²⁺ substitution for Ca²⁺, while leftward shifts (e.g., 25.9° → 25.7°) implied lattice strain from Sn²⁺ ions. Below 600°C, crystallinity improved with annealing; above 800°C, secondary phases (e.g., Ca₂P₂O₇ and SnO₂) appeared, suggesting partial decomposition. Ethanol minimized Sn oxidation and enabled uniform Sn²⁺ incorporation. Acidic media resulted in broader peaks, likely due to point defects and cation vacancies, which could be beneficial for bioactivity but less ideal for structural integration.
Conclusions
Sn-HAp synthesized in ethanol and annealed at 600°C yields a structurally stable, enamel-like material with Sn²⁺ effectively integrated into the HAp lattice. This bioinspired material offers promising long-term desensitizing performance. Ethanol-based synthesis is preferred for applications requiring high crystallinity and biostructural fidelity. Acidic synthesis, while less structurally precise, may offer potential for bioactive or resorbable materials. Future research will focus on optimizing Sn content and evaluating in vitro bioactivity.
