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Abstract
In the early mineralized enamel crystals, ribbon-like crystals appear near the ameloblasts. Some ribbon-like crystals showed helical or spiral structure within restricted environment during the preparation of embryonic bovine specimens for electron microscope. These specimens did not suffer from the cutting damages nor staining effects. The main cause of the helix structure is considered a result of the dehydration during preparation. The periodic structure must reflect the regularity of initial enamel crystals. If dehydration caused the ribbon-like crystal to induce the periodic helix, it is one possibility that the earliest enamel crystal is OCP which has been proposed as a precursor of HA. Because it is considered that OCP is more sensitive to dehydration and more symmetric structure than biological HA. The periodicity of the helical ribbon-like structure was about 25 to 55 nm long and could be compared to the periodicity of organic helices which had observed in an immature rat enamel.