Crystal growth in rat incisor enamel

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Abstract
The width and thickness of hydroxyapatite crystals and the crystal density at various stages of rat incisor amelogenesis were studied using electron microscopy. The cross‐sectional profile of the crystals increased from 259 × 12.7 Å at the surface of the ameloblast to 454 × 249 Å in the completely mineralized enamel. In agreement with previous observations, many crystals had a regular, flattened hexagonal profile during the matrix formation stage. During enamel maturation, the crystals assumed more irregular surface contours, the crystals tending to adapt themselves to the available space. In completely mineralized enamel, the crystals were as irregular in shape as the crystals in human enamel, and they occupied around 85% of the volume. While the crystals at the onset of mineralization were separated by a distance of 120–150 Å, the crystals eventually became relatively closely packed, separated by a fine space only 10–25 Å in width. A lower number of crystals per unit cross‐sectional area of the enamel prisms was observed in fully mineralized enamel as compared with the early stages of amelogenesis. Since evidence of fusion of crystals is lacking, the decrease in crystal density appears to result from swelling of the enamel prisms.