High Resolution STEM Images of the Human Tooth Enamel Crystals

Abstract

High-resolution scanning transmission electron microscopy (STEM) images of human tooth enamel crystals, mainly in the high-angle annular dark-field (STEM-HAADF) mode, are presented in this work along the [1000], [10-11]. and [1-210] directions. These images allow knowing some structural details at the nanometric level of the human tooth enamel crystals and of the central dark line (CDL) observed at their centers. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images of the CDL showed the Fresnel contrast. In the STEM bright-field (STEM-BF) and annular-dark-field (STEM-ADF) images, the CDL was observed as an unstrain hydroxyapatite (HAP)-like zone but surrounded by a strained zone. In the STEM-HAADF images, the CDL appeared with a weak contrast, and its contrasts’ thickness was registered between 3 and 8 Å. The arrangement obtained in the STEM-HAADF images by identifying the bright points with the Ca atoms produced the superposition of the HAP atomic sites, mainly along the [0001] direction. The findings provide further information on the structure details at the center of enamel crystals, which favors the anisotropic carious dissolution at the CDL.

Multi-resolution Correlative Ultrastructural and Chemical Analysis of Carious Enamel by Scanning Microscopy and Tomographic Imaging

“…In addition to the crystallite shapes and demineralized region, the lattice was seen in some locations, providing a level of detail likely to provide additional insights into caries (SI-Figure S40). However, similar to the adverse effects caused by repeated exposure to X-rays, sample damage was observed (SI-Figure S40c), as previously reported …”

“…However, similar to the adverse effects caused by repeated exposure to X-rays, sample damage was observed (SI-Figure S40c), as previously reported. 63 In addition to ptychography, differential phase contrast (DPC) imaging was also carried out with a step of 50 nm simultaneously to the XRF in I14 (DLS) with the benefit of coregistration with a similar resolution for both techniques. Different phase contrast retrieval data correlated well with the SEM images with the observation of sheath region for instance in the surface region, a differentiation in the structure in rods and inter-rods.…”

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

“…All of the aforementioned developments described in this review led to new advances in research on enamel and other mineralised tissues; however, there is a necessity to correlate the findings of synchrotron-based experiments with other techniques such as polarised transmitted light microscopy [ 145 ], FIB-SEM [ 39 ], (S)TEM [ 190 ], radiography/tomography [ 145 ], optical coherence tomography (OCT) [ 696 ], polarization sensitive OCT [ 697 ], APT [ 698 ], Raman spectroscopy [ 168 ], X-ray photoelectron spectroscopy [ 699 ], AFM [ 700 ], mechanical tests [ 701 ], proton induced X-ray emission (PIXE) [ 702 ], neutron [ 703 ], time-of-flight secondary ion mass spectroscopy (ToF-SIMS) [ 704 ], and indentation [ 142 ], to develop a suitable sample preparation workflow and to tackle the disease with a multi-scale multi-correlative characterisation technique strategy.…”

“…Using tomography, measurement of the porosity (based on grey values) of the demineralised and non-demineralised regions was carried out [ 57 ], as well as their density variation and the decrease in the carious lesion [ 142 ], Figure 2 d. In addition, the chemical composition was also investigated in carious and normal enamel using Raman spectroscopy/Raman peaks [ 136 , 188 ], as well as the difference found in calcium K α fluorescence intensity in rod and inter-rod in carious enamel using X-ray fluorescence spectroscopy (XRF), Figure 2 d. The underlying cause of enamel susceptibility to acids has sparked interest in investigating the possible points of weakness that initiate demineralisation. For this purpose, researchers have investigated nano-characterisation techniques (e.g., TEM, APT) and synchrotron X-ray absorption spectroscopy (XAS), to provide details about potential locations of the initiation of demineralisation, Figure 2 d. Such locations include a high angle grain boundary (113.5°) between HAp crystallites, a structural defect located in the crystallite HAp referred to as ‘central dark line’ (CDL) with a width of ~1 nm [ 189 ] (the CDL has been extensively investigated [ 190 , 191 , 192 ]) ( Figure 2 d), organic phase [ 88 ] ( Figure 2 d), chemical composition creating residual stress [ 193 ] and defects [ 9 , 194 ], or the striae of Retzius previously mentioned.…”

Amelogenin-inspired peptide, calcium phosphate solution, fluoride and their synergistic effect on enamel biomimetic remineralization: an in vitro pH-cycling model

“…Enamel formation is a typical biomineralization process that requires synergistic interaction of both organic and inorganic components [ 14 ]. Therefore, based on the principles of biomineralization, efforts in tissue engineering were directed to develop biomimetic remineralization systems that demonstrate promising potentials for the regeneration of enamel’s hierarchical microstructure and its mechanical performance [ 15 , 16 ].…”