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J Mater Sci: Mater Med (2008) 19:877882 DOI 10.1007/s10856-007-3174-7
STEM-HAADF electron microscopy analysis of the central dark line defect of human tooth enamel crystallites
Jose Reyes Gasga Georgina Carbajal-de-la-Torre Etienne Bres Ivet M. Gil-Chavarria Ana G. Rodrguez-Hernndez Ramiro Garcia-Garcia
Received: 31 October 2005 / Accepted: 17 May 2007 / Published online: 1 August 2007 Springer Science+Business Media, LLC 2007
Abstract When human tooth enamel is observed with the Transmission Electron Microscope (TEM), a structural defect is registered in the central region of their nanometric grains or crystallites. This defect has been named as Central Dark Line (CDL) and its structure and function in the enamel structure have been unknown yet. In this work we present the TEM analysis to these crystallites using the High Angle Annular Dark Field (HAADF) technique. Our results suggest that the CDL region is the calcium richest part of the human tooth enamel crystallites.
Introduction
Human tooth enamel is composed by 96 wt% of inorganic material, mainly hydroxyapatite (HAP), and 4% of organic material, consisting essentially by two classes of proteins: amelogenins and enamelins. Enamel is formed by prisms in
the size range of tenths of microns, which run from the enameldentin junction to the enamel surface. These prisms are formed by many elongated-plate-like crystallites whose diameter is from 50 nm to 100 nm wide and from 300 nm to 500 nm long, approximately. The enamel crystallites are observed with the transmission electron microscope (TEM), exhibiting a line of 11.5 nm width along their centers [16]. This line has been named as central dark line (CDL), although its contrast is focusing dependent: it is dark in under-focus, disappears when the image goes through focus, and it is white in over-focus [4], resembling the Fresnel fringes behavior in a phase-contrast image. The observance of this CDL both in plan view (transversal) and along cross-sectioned view (longitudinal) enamel samples indicates that it certainly corresponds to a plane but not to a line. However, central dark line has been the name used to identify it.
In order to visualize its structure, the CDL has been attributed to the presence of planar defects such as dislocations and grain boundaries [79], to the presence of a layer of octocalcium phosphate (OCP) in dentine crystals [10], and...