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 microns in length, some 4-7 microns 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.

Summary: Elastic system fibers (ESFs), i.e., microfibrils (putative oxytalan fibers), elaunin and elastic (true elastin) fibers, in the rat mandibular joint were studied mainly using scanning electron microscopy (SEM) and light microscopy (LM) with the aid of image processing. The present quantitative analysis using LM showed that the articular disc and capsule, which are the sites that receive physical compressive force during mastication, contained more ESFs than the articular cartilage of the mandibular joint. In addition, oxytalan fibers were the principal ESFs in all the articular components (capsule, articular disc, supraosseous layer of articular surfaces and articular cartilage). Subsequently, ESFs in the articular disc, which contained more thick ESFs, were closely examined by SEM using both collagen-and elastin-digestion methods. SEM showed networks of microfibrils beneath the articular surfaces (superior and inferior layers) in the thin central portion of the articular disc; the principal microfibrils ran at nearly right angles to the collagen fibers. The microfibrils were cemented with amorphous elastin, thickened and shifted towards interconnecting oblique fibers and many main ESF trunks, which were oriented in the direction of the layered wavy collagen fibers and parallel to the direction of applied force, to sustain the mechanical force. From the superior and inferior layers, the main ESFs shisfted towards the middle portion of the disc, transitional zone (synovial osteochondral junction) and the other articular components, showing no specific directivity. Transmission mission electron microscopy revealed that the thick main ESFs in the elastic network were elaunin fibers. The present study indicated that ESFs unite, branch and therefore construct an extensive and complicated protective stretchable network, which is interposed with the less tensible collagen network in the mandibular articular disc.Elastin system fibers (ESFs), which are usually differentiated as microfibrils (oxytalan fibers), elaunin and elastic fibers based on their staining properties and the distribution of the microfibrils and amorphous cementing elastin, play a particularly important role in the elasticity of connective tissue (CottaPereira,