Organized Assembly of Fluorapatite Nanorods Controlled by Amelotin: Implications for Enamel Regeneration

Abstract

Dental enamel possesses remarkable mechanical properties because of the hierarchical structural organization and hybridization of organic and inorganic components. Amelotin (AMTN), as an enamel matrix protein, plays a critical role in the formation of a compact aprismatic hydroxyapatite (HAP) surface layer at the maturation stage of enamel biomineralization. However, its action mechanism remains largely unclear. Here we used in situ atomic force microscopy (AFM) to image the transition from an amorphous calcium phosphate (ACP) precursor phase to fluoro-substituted HAP (F-HAP) under the influence of AMTN. In the presence of F- ions only, F-HAP nanorods formed randomly on the ACP surface but assembled in an orderly manner in the presence of 1 μM AMTN. Using transmission electron microscopy (TEM), we observed a stepwise nucleation mechanism from prenucleation clusters to rod-like crystals templated and modulated by AMTN. Mechanical measurements of nanorods surface revealed the enhanced modulus of the layers with organized nanorods of F-HAP. Our findings emphasize that AMTN plays an important role in modulating crystallization and organization of F-HAP crystals in enamel, which is significant for potential synthesis of dental restoration materials.