A polarization microscopic and micro X-ray diffraction study on the organic matrix of developing human enamel

Abstract

Ground sections from enamel of developing deciduous incisors of stillborn infants were demineralized in EDTA. The demineralized sections were immersed in a series of media with refractive indices ranging from 1.40 to 1.66 and the retardation of polarized light was measured in selected areas. The 75 imbibition curves obtained exhibited the typical parabolic shape characteristic of form birefringence and from the minima of these curves the refractive index of the organic matrix was calculated to be 1.560 ± 0.006. After freeze-drying, the organic content in the areas investigated optically was determined by contact microradiography. From the amount of organic matter and the birefringence in corresponding areas, the intrinsic birefringence of the enamel organic matrix was (+)0.0003 ± 0.0001. Micro X-ray diffraction patterns were recorded from the areas earlier investigated. All patterns contained a relatively intense ring at 4.7 Å and a fainter broad ring at 9.7 Å. None of these showed maxima indicative of preferred orientation of the protein macromolecules. From the results obtained by the different methods of investigation, it is concluded that the organic matrix of dental enamel is arranged in the form of submicroscopic elongated micelles more or less parallel to the direction of the enamel prisms. The organic material constituting these elongated elements seems on the other hand to be completely disordered at the molecular level.