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.
Highlights
Considering that the scanning transmission electron microscopy (STEM)-high-angle angular dark-field (HAADF) images depend on the atomic number of the sample and that Z = 20 for Ca, Z = 15 for P, Z = 8 for O, and Z = 1 for H, the bright spots are related to the Ca atoms, followed in intensity by the P atoms
The crystalline periodicity can be clearly observed in the enamel crystals, and neither planar defects nor dislocations were directly observed in the central dark line (CDL) region
Taking that the brightest points corresponded to the Ca atom positions in the HAP unit cell, and the line indicates the CDL position, Figure 6b shows the arrangement generated
Summary
The human tooth is made up of dentin, which is a connective tissue that gives shape and stiffness. Dentin is covered by enamel, the most wear-resistant tissue in the human body. Enamel is responsible for protecting teeth from wear and tear caused by chewing as well as corrosion from acids produced from food debris. The dentin–enamel junction zone is where dentin meets enamel. Dentin is made up of a 70% inorganic material, a 20% organic material, and 10%
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