Abstract The inorganic matter in human tooth enamel (HTE) is related to the hexagonal unit cell of hydroxyapatite (HAP), but carbon, magnesium, and sodium are also detected by Energy-Dispersive X-ray spectroscopy (EDS) in addition to HAP’s elements. These elements are attributed to ionic substitutions within the HAP unit cell, where Ca 2+ ions are partially replaced by Mg 2+ and Na + ions, and the PO 4 3− and OH − ions are partially replaced by carbonate (CO 3 2−) ions. Simulations of HAP-related structures have indicated that these substitutions induce a slight distortion, transforming the unit cell from hexagonal to triclinic. Therefore, with the aim of recovering the hexagonal system for HTE, a 3 3 1 3 × 3 × 1 hexagonal supercell based on the HAP unit cell including the additional CO 3 2−, Mg 2+ and Na + ions was generated. However, the crystallographic elements observed in the convergent beam electron diffraction (CBED) patterns indicate that the system remains triclinic. Graphic Abstract
Reyes-Gasga et al. (Thu,) studied this question.