Epithelial anlagen of human third dentition and their migrations in the mandible and maxilla.

Human teeth are diphyodont excepting the permanent molars. The deciduous teeth are, ontogenetically considered, the first generation of teeth. The permanent teeth (except molars) belong to the second dentition. The term " third dentition " (also called the postpermanent dentition) refers to the opinion that one more set of teeth can occur in addition to the permanent teeth. The processes by which the permanent teeth (second dentition) originate from the deciduous teeth (first dentition) and the changes of positions of the former in relation to the latter were already studied by the present author (1965, -68). W. L e c h e (1893) observed the anlagen of the third dentition in some mammals. C. Rose was the first to notice the presence of epithelial anlage of human third dentition (1895). H. Ahrens (1913), although he observed the same histological structure, took it merely for a free end of dental lamina. T. Fuji ta (1943) emphasized the phylogenetic significance of this structure. However, the previous studies lack detailed descriptions, so that there remain as problems in what teeth and when the anlage of the third dentition appears and what changes of position it undergoes in regard to its predecessors (permanent teeth). Therefore, the author studied those problems and obtained some new findings which are described in the present paper.