Transmission electron microscopy (TEM) samples of dentine were prepared by ion beam thinning using a liquid nitrogen cooled holder, 4 to 5 kV Ar+, 70–100 μA beam. The samples were fresh, unfixed, and not subjected to mechanical deformation or dissolution. They were examined at 80 or 100 kV in the TEM, when contrasts were due entirely to the mineral component. Parallel pairs of elongated electron dense features extended for distances exceeding the collagen D period, appearing as electron dense circles in “transverse section”. These images are interpreted as indicating the deposition of mineral around collagen microfibrils. The repeat distance between close packed pairs of dark lines ranged from 38 Å upwards. There was little regular packing of the electron dense circles (or dots) seen in “transverse
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