Characterization of elemental distribution across human dentin-enamel junction by scanning electron microscopy with energy-dispersive X-ray spectroscopy.

The human dentin-enamel junction (DEJ) is a natural junction that unites two dissimilar mineralized tissues in the human tooth: enamel and dentin. DEJ plays a critical role in maintaining structural and functional integrity of the tooth. However, its structure, chemical composition and function remain unclear and controversial. Systematic investigation of elemental distribution across human DEJ is still lacking in the literature. This study aimed to investigate the elemental distributions of Ca, P, O, C, N, Na, and Mg across the DEJ of human teeth using scanning electron microscope with energy dispersive spectroscopy of X-ray. The results revealed abrupt changes in the distributions of six elements (C, N, Ca, P, Na, and Mg) across the DEJ. Specifically, the four mineral elements showed similar level of change in distribution, with Ca, P, Na decreasing while Mg increasing by 21%-25% from enamel to dentin side of the DEJ. The two organic elements C and N showed much larger changes in distribution, with C increasing by ~150% and N increasing by ~270% from enamel to dentin side of the DEJ. The slope of the distribution curves across the DEJ was estimated to be ~2 μm in width and coincided with the phase intermixing of the micro-scallop structure of the DEJ.