Journal of the Japanese Association of Regenerative Dentistry
J Jpn Assoc Regenerative Dent_Vol.2(2)_pp.138-158
ISSN 1348-9615


Enamel crystal development

Yukishige KOZAWA1, Atsushi OOKUBO1,3, Hirokazu OINUMA1, Hideki CHISAKA1, Tomohisa HONDA1,2, Rumi YOKOTA1, Yuka IWASA1, Kunihiro SUZUKI1, Hitoshi YAMAMOTO1, Toshiro SAKAE1
1Department of Anatomy II, Nihon University School of Dentistry at Matsudo,
2Department of Orthodontics, Nihon University School of Dentistry,
3Japan Institute for Advanced Dentistry

The initial calcification of enamel was observed by the high resolution electron microscope. With gultalaldehyde fixation, the granular or amorphous structure at 20-50 nm in diameter and rod like structure of 20-50 nm in width having high density fibers in the center, were observed near the Tomes process of the ameloblasts. The grainy materials at 20-50 nm in diameter secreted by the ameloblasts were observed, when the animals were fixed with tannic acid.
The hollow structures located to a distance of the several 100 nm from the cell membrane. And also the tubular structures had high density fibrils in the center. The diameter of these two structures was same as about 20-50 nm. The central fibers formed as twisted threads, strands or beads were less than 1 nm in diameter, were similar size of the atoms composed of apatite crystal.
These phenomena showed the pattern of initial enamel crystals. The amorphous stippled materials fused and formed the tubular structures, which were enamel protein secreted by ameloblast. The hydrophobic small part of the enamelin captured the molecules or atoms of apatite crystal elements. Atoms and molecules accumulated in the tubule and arranged irregularly to form the strand structure in the center. As the result, the initial precursor of crystal formed in the tubular structures. It is to say the precursor hardly packed by the amorphous organic materials of enamel protein. It is the reason that the structure was insoluble by the acid attack and stained with lead-acetate. It is concluded that this amorphous structure is the precursor of initial enamel crystal.
The c-axis of the crystal growth is decided by the arrangement of these tubular structures of enamelin, which was the crystal developing in the place. The tubules arranged almost perpendicular to the cell membrane of Tomes process, because the C-terminal of the enamelin had an affinity at the cell membrane of the secreting face of Tomes process, the N-terminal attached to the sheathlin in the cross striation of enamel prism.
When atoms accumulated and saturated in the tubular structures, the amorphous precursor crystal, so called as strands or crystal nuclei, changed suddenly to the apatite crystal, having several lattices of atomic images, by the thermal energy potential. This initial crystal was recognized ribbon-shaped crystal of enamel. Next, the atoms adhered on the side of these crystals and grew to the plate forms. These plate-crystals increase the thickness, and finally changed to a hexagonal cylinder shape with the epitaxial growth. New crystallization of the precursor of crystals always occurs between crystals, and new crystals fused matured hexagonal crystals. Finally these crystals formed the irregular polygonal crystals. These processes take place in the spaces of dissolved amelogenin.
In other words, the crystal size and form were depended on the shape and size of the space of the amelogenin, because the spaces appeared by the dissolve of amelogenin.

Keyword: enamel, crystal formation, crystal precursor, calcification, biomineralization