Three-dimensional observations of the relation between the natural enamel surface and the outermost layer in human permanent tooth.

A coronal enamel surface of a human permanent tooth and the exposed outermost layer etched with phosphoric acid or EDTA were observed in the same field by means of scanning electron microscopy. Gross structural patterns of the enamel surface were either of a flattened type showing no perikymata patterns of of undulating and overlapping types with grooves and convex ridges. The undulating and overlapping patterns showed an alternating structure of rows of numerous shallow and deeper prism-end pits or that of these pit rows combined with a smooth band. The pit rows were usually located in the grooves with succeeding slopes in the middle of coronal enamel, but, towards a cusp, they often existed in the convex ridges. The striae of Retzius reached the grooves of perikymata from cervical to the middle of coronal enamel; however, the arrangement of the striae did not always follow perikymata patterns towards a cusp. The overlapping pattern in cervical enamel and the flattened type in cuspal and cervical enamel usually had uniform structures of shallow, indistinct, or no prism-end pits. The surface 'prismless' layers containing indistinct prism structures were observed under these uniform structures.