Structure of human dentine—I: Phase contrast, polarization, interference and bright field microscopic observations on the lateral branch system

Abstract

Examination of human dentine by phase contrast microscopy has revealed that the odontoblast process gives rise to large numbers of lateral branches. Large branches with a diameter of 0·25–0·5μ leave the main process from all sides at intervals of 1.0–2.0μ. Smaller branches with a diameter of 0.2μ or less arise directly from the main process or from the large branches, and occur throughout the matrix. Both the matrix, and the processes and large branches are biréfringent when viewed with the polarizing microscope. The processes and large branches display a birefringence colour different from that of the matrix, reflecting a difference in their structure and/or composition. The pericanalicular matrix was shown to have a major orientation at right angles to the long axis of the dentinal canal. It may also have a spiral component around the canal. The refractive index of the odontoblast process was measured with an interference microscope. The values obtained ranged from 1.414 to 1.493, and are in the range of values generally given for cytoplasm. The large lateral branches have been shown to have the same range of refractive index values by use of appropriate mounting media. Measurements of the refractive index of the matrix gave values of 1·7132–1·8699, indicating that its structure and/or composition are distinctly different from those of the processes and large branches. The difference in the magnitudes of these values also accounts for (1) the clarity of demonstration of the odontoblast processes and their branches with the phase contrast microscope, and (2) for the colour differences in birefringence seen with the polarizing microscope. Dentine sections stained with thionin display a pattern of parallel and concentric bands, which are also visible with polarization and interference methods. The darker bands, approximately 0.5μ in width, alternate with lighter bands, approximately 1.0–1.5μ in width. They appear to be produced by an intimate association between large lateral branches and bands of collagen matrix.