The arrangement of crystallites in enamel prisms

Abstract

A series of X-ray diffraction patterns has been recorded from sections of permanent and deciduous human enamel. The sections were cut in three different planes so that an idea of the spatial arrangement of the crystallites could be found. From any point in the enamel the pattern consisted of arcs of reflection, the variation in crystallite orientation being indicated by the limits of the arcs, and the mean direction of orientation being shown by a line joining the midpoints of the two 002 reflections. In cuspal enamel of longitudinal sections and in enamel cut in the transverse oblique plane, the mean direction of the crystallites was parallel with the direction of the prisms. In enamel on the sides of the crown (lateral enamel) in longitudinal sections, the mean direction of orientation was displaced away from the prism axes towards the cervical margin. No true “double” orientation of crystallites within the prism complex was demonstrated. This was in agreement with a new interpretation of the optical behaviour of enamel between the crossed polars of a polarizing microscope. There appeared to be a gradual change in the orientation of crystallites from one side of a prism to the other. Such a pattern would account for the features of enamel structure observed here and would agree well with the appearance of enamel as seen with the electron microscope. Occasionally, diffraction patterns with two sets of arcs were recorded but they were the result of including two differing layers of enamel in the X-ray beam. Specimens producing such an artifact have been used to demonstrate the cause of the asymmetric, distorted reflection patterns which are frequently obtained when working with calcified tissues.