A Histological Study of the Organic Elements in the Human Enamel focusing on the Extent of the Odontoblast Process

Abstract

Topographic and tomographic studies were conducted on the organic elements occluded in the enamel of premolars removed from young orthodontic patients by using light (transmitted) microscopy, confocal scanning laser microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) on ultrathin sections and freeze-etching replicas, and energy dispersive spectroscopy (EDS) X-ray microscope (EDX) analysis. The present fine structure study aimed in particular to determine the fine structure of the enamel spindle and the extent of the odontoblast process. Organic elements in the ground-sectioned enamel corresponding to simple projections and enamel rods/spindles, enamel tufts and lamellae were identified by conventional light microscopy and subsequently examined by CLSM. Both light microscopy and CLSM indicated that a number of enamel spindles were measured about 50 μm in length, some 4-7 μm in thickness and were mostly confined to the cuspal summits and conformed to previous descriptions. SEM examination revealed some simple projections extending from the dentine into the enamel as well as clearly identifiable enamel spindles; the enamel spindles were structures intervening enamel prisms and showing morphological complexity by branching and convergence of the distal endings of the invading organic structure from dentinal tubules. EDX-analysis revealed that enamel tufts, lamellae, and spindles contained less phosphorus and calcium elements than enamel prisms. The enamel spindles had a higher content than tufts or lamellae, but this may be the result of contamination from surrounding enamel. Both conventional ultrathin-section and freeze-etching replica TEM evaluation of the dentino-enamel boundaries in particular suggested that simple projections and enamel rods/spindles were extensions of the odontoblast processes trapped in the enamel during early amelogenesis. In contrast, both SEM and TEM observations failed to identify dentinal tubule, peritubular (intratubular) dentine, membranous structures or lamina limitans surrounding the enamel spindles and simple projections occluded in the human enamel.