Root formation in ectopically transplanted teeth of the frog, Rana pipiens I. Tooth morphogenesis.
In order to determine the intrinsic (genetic) and extrinsic (functional) parts of the naturally ankylosed tooth, a qualitative study of the development and fate of tooth buds transplanted individually or within the premaxilla was carried out. These teeth were transplanted as autografts during crown formation. They were placed in either the anterior chamber of the eye or in a dorsal subcutaneous site. Most of the 163 transplants survived and were examined at intervals from 0 to 180 days by gross, histologic and microradiographic methods. Tooth buds transplanted with or without the premaxilla were capable of growth to normal size and shape. Lack of underlying bone with which to ankylose and lack of normal oral environment and function did not prevent formation of a normal-sized root area. The root area was composed of dentin and covered by a solid, undisrupted Hertwig's epithelial root sheath which appeared to mold the root. Calcified tissue formed on the outside surface of dentin only when the root sheath was accidentally torn during transplantation.