Mechanically Reinforced Artificial Enamel by Mg²⁺-Induced Amorphous Intergranular Phases

Abstract

Amorphous intergranular phases in mature natural tooth enamel are found to provide better adhesion and could dramatically affect their mechanical performance as a structure reinforcing phase. This study successfully synthesized an amorphous intergranular phase enhanced fluorapatite array controlled by Mg 2+ (FAP-M) at room temperature. Furthermore, atom probe tomography (APT) observation presents that Mg 2+ is enriched at grain boundaries during the assembly of enamel-like fluorapatite arrays, leading to the formation of intergranular phases of Mg-rich amorphous calcium phosphate (Mg-ACP). APT results also demonstrated that the segregation of Mg 2+ caused the chemical gradient in nanocrystalline attachment and realignment under the drive of inherent surface stress. These results indicate that the amorphous intergranular phases served like glue to connect each nanorod to reinforce the enamel-like arrays. Therefore, the as-received FAP-M artificial enamel exhibits excellent mechanical properties, with hardness and Young's modulus of 2.90 ± 0.13 GPa and 67.9 ± 3.4 GPa, which were ∼8.3 and 2.2 times higher than those of FAP arrays without controlled by Mg 2+ , respectively.

Role of Inorganic Amorphous Constituents in Highly Mineralized Biomaterials and Their Imitations

“…This composite shows a several-fold enhancement of PLA toughness as well as outstanding improvement in load-bearing capacity and viscoelastic figure of merit, which can be attributed to the amorphous phase of alumina as well as the lamellar structure . Recently, the use of amorphous TiO 2 and intergranular ACP phase for mechanical enhancement in artificial biomaterials was also demonstrated. , …”

“…89 Recently, the use of amorphous TiO 2 and intergranular ACP phase for mechanical enhancement in artificial biomaterials was also demonstrated. 75,90…”

The nonclassical crystallization mechanism and growth kinetics of densely packed fluorapatite nanorod arrays: effects of the ion transportation rate and fluoride concentration

“…High resolution TEM (HRTEM) images of these nanoparticles showed no lattice fringe, suggesting that they were amorphous, which could act as the precursor for subsequent attachment to FAP crystallites. 36 To characterize the grown FAP on the enameloid substrate at an early stage, a thin lamella from a sample after reaction for 12 h was prepared with FIB, milling from the surface down to the enameloid. According to the TEM image, the underlying natural enameloid crystallites below the red dotted rectangular box were homogeneous and each crystallite possessed a distinct outline, while many 5–10 nm electron-lucent nanopores appeared on the grown FAP crystallites in a vague shape, as indicated by white arrows in the upper region in Fig.…”

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

“…Human enamel was investigated, to analyse the Mg K-edge, and was compared with Mg ACP [ 92 , 193 ], revealing similarities in the enamel structure, as well as comparisons with rodent enamel, showing the presence of Mg in the crystallite cores. These results were combined with other nanocharacterisation techniques, such as APT and TEM, to model the amelogenesis process, as well as to provide detail about residual stress in enamel crystallites from chemical gradients [ 193 , 671 ], Figure 8 i. It was suggested that residual stress leads to an increase in the solubility of crystallite cores compared to the surrounding, which was visualised as a preferential demineralisation of the crystallites.…”