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Enamel Rod Morphology

This block of enamel is composed of enamel rods packed tightly together. Rods have a "key-hole" (fish-like) shape - each one having a head and a tail. The rods are oriented so that the heads face toward the cusp tip and the tails toward the cervical margin. The enamel crystallites that compose each rod exhibit differing orient-ation within these two regions. The crystallites are composed of hydroxyapatite (90% of the inorganic component of mature enamel). The space between the crystallites is occupied by the organic matrix (2%) and water (12%). Figures 1, 2, and 3 show several arrangements of enamel rods reported in the teeth of various species. The key-hole arrangement (#2) is considered to be the predominate one found in humans. However, in the regions of the cusps and cervical margins variations are not uncommon.


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