Root formation in ectopically transplanted teeth of the frog rana pipiens. II. Comparative aspects of the root tissues.

In the second part of an experimental study of the behavior and fate of the roots of ectopically transplanted frog teeth the comparative aspects of the tooth root and its tissue composition were examined. Experimental results showed that the root or pedicel area of the frog tooth was an intrinsic part of the tooth. The tooth was capable of growth to normal size and shape with or without the presence of underlying bone. When compared with existing descriptive exidence and analysis it was determined that the best terminology for the amphibian root tissues would be dentin right up to the point of attachment where cellular basal bone is seen. This is because it is an intrinsic part of the tooth, if formed on the pulpal side of the root sheath, and is formed by odontoblasts. Because of the above observations, the original Hertwig's epithelial root sheath appeared both homologous and analogous with the mammalian sheath, but since all the root tissues were under this sheath, no tissues homologous to any of the paradental tissues of cementum, periodontal ligament, or alveolar bone could be found except when the root sheath injury resulted in induction of an acellular tissue upon the outer surface of dentin.