[The morphological and histochemical characteristics of the interprismatic structures and the human enamel. A light microscopy study (corrected)].

Inter-rod structures of human enamel were investigated at the light microscopic level in order to define their morphology as well as the presence and distribution of both organic and inorganic molecules inside them. The histologic procedure employed in the present study allowed us to obtain 100 (microns) thick sections from permanent teeth without previous decalcification and paraffin or resin embedding. Three inter-rod structures were identified in the innermost area of the enamel on the basis of their morphologic aspect, namely the endings of dentinal tubules, the spindles and structures with a spherical or ovoidal shape never described before and by us denominated spheroids. Both spindles and spheroids were connected to one or more dentinal tubules which cross the dentin-enamel junction. Measurements performed on all the specimens led to establish the real dimensions of the inter-rod structures. Histochemical staining carried out with selective dyes showed that spindles and spheroids were quite alike similar to each other as far as chemical composition and molecule distribution are concerned. Both structures contained calcium salts, glycosaminoglycans, glycoproteins, but not collagen. The endings of dentinal tubules among the rods showed histochemical characteristics similar to those of spindles and spheroids. On the basis of the above findings, spindles and spheroids could have a dentinal origin, and so likely derived from the metabolic activity of odontoblasts during the tooth-germ development. Whether they are embryonic vestigia without a functional role or are receptors which transmit signals to nerve endings in dentin and pulp remains to be clarified.