Preparation of amorphous calcium phosphate nanoparticles using small organic molecules for biomimetic mineralization of dentin

Abstract

The development of nanomaterials capable of effectively occluding dentinal tubules and inducing biomimetic mineralization is critical for treating dentin hypersensitivity and early-stage caries. Owing to its high reactivity, amorphous calcium phosphate (ACP) serves as an ideal mineralization precursor. Although organic molecules are known to modulate and stabilize ACP, how small organic molecules (SOM) with distinct functional groups influence its remineralization efficacy remains incompletely understood. In this work, phytic acid (IP6) and cyclohexanehexacarboxylic acid (H6L), two structurally analogous yet functionally distinct molecules, were used as regulators to synthesize organic/ACP nanocomposites, denoted as IP6/CaP and H6L/CaP, respectively. A control sample prepared without organic additives was denoted as CaP. These composites were systematically evaluated for their ability to occlude dentinal tubules, promote remineralization, and resist acid challenge, using commercial 45S5 bioactive glass (BG) as a positive control. Material characterization revealed that the CaP comprised hydroxyapatite with an average particle size of 548.75 ± 2.32 nm. In contrast, both IP6 and H6L facilitated the formation of uniformly distributed microscale round-shaped aggregates, yielding IP6/CaP and H6L/CaP with average diameters of 87.64 ± 2.37 nm and 99.56 ± 1.67 nm, respectively. In vitro mineralization assays showed that IP6/CaP induced a uniform, dense nanomineral layer on both the dentin surface and type I collagen, achieving optimal integration within the collagen matrix. H6L/CaP led to the formation of uniformly distributed microscale round-shaped aggregates, whereas CaP produced disordered, loosely packed large crystals, indicative of poor mineralization quality. Dentinal tubule occlusion tests demonstrated that IP6/CaP and H6L/CaP afforded significantly superior sealing and acid resistance compared to both CaP and BG. Cytotoxicity assays confirmed the good biocompatibility of all materials. In summary, both IP6 and H6L effectively stabilized ACP and inhibited its phase transformation to hydroxyapatite. Notably, IP6/CaP outperformed both CaP and H6L/CaP in dentin remineralization and tubule occlusion, providing valuable guidance for the rational design of next-generation materials for dental desensitization and hard tissue regeneration.