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PubMed1978

Tooth ontogeny in the upper jaw and tongue of the rainbow trout (Salmo gairdneri).

Tooth development has been studied in the upper jaw and tongue of a series of rainbow trout embryos (Salmo gairdneri). The sequence of tooth ontogeny in the maxillary bone differs significantly from that seen in the premaxillary bone. In the maxillary bone the teeth developed in an almost perfect alternating sequence from front to back, the teeth occupying the odd-numbered tooth positions developing ahead of those occupying the even-numbered tooth positions. However an alternating sequence was not encountered in the premaxillary bone of the rainbow trout where, from tooth position 4, teeth developed in sequence, and at approximately the same rate, in both directions. The significance of this difference was discussed. The teeth on the tongue developed in an alternating sequence, the fourth tooth developing first followed by the second tooth. The teeth in positions one, three and five later developed simultaneously. Evidence was presented which indicated that resorption of a tooth may commence from its pulpal surface in association with the appearance of multinucleated giant cells and not from the external surface in relation to a successional tooth. This was particularly so in the case of lingual teeth where the successor was laterally positioned or in midline teeth which lacked successional teeth.

Animals↗
PubMed1978

On the potential of the adult rat incisor odontogenic organ to differentiate into two intact teeth.

The odontogenic organ of 10 male albino rats weighing 200 g has been exposed by a longitudinal incision through the masseter muscle. Its site could be identified as a bluish elevation of the mandible. Into this region through the bone, a 2 X 2 mm. tinfoil has been inserted, deep into the odontogenic organ. The tinfoil direction was generally parallel or slightly oblique to the tooth longitudinal axis. The animals were killed after 1 month. Their lower incisors in the bony sockets were fixed and decalcified, cut sagittally and processed histologically. In 3 sockets two separate teeth could be identified, a labial and a lingual tooth. Generally only the labial tooth was covered by enamel, in one case however both teeth exhibited a regular enamel layer. Both teeth were separated by a periodontal ligament and exhibited separate tooth cavities. This experiment demonstrates the capability of the odontogenic organ to reproduce a whole new complex organ, the tooth. A phenomenon hitherto observed only in Urodela in which a severed limb regenerates from primitive pluripotential stem cells known as blastema. Contrary to the newt however, the incisor blastema reproduces continuously throughout the life of the individual and responds to the tinfoil stimulus by a production of an extra tooth.

Animals↗
PubMed1988

Coated pits and vesicles in the osteoclast.

The osteoclast is a cell with a phagocytic ability not dissimilar to the macrophage. Nevertheless, the mechanisms by which it resorbs bone are poorly understood. The aim of this study was to examine the distribution of coated membrane structures in the osteoclast in order to gain further information about endocytosis in this cell. Osteoclasts around the developing tooth germs of young rats were examined using transmission electron microscopy, and immunocytochemistry. Results showed that previously described coated membrane structures within the ruffled border do not appear to be associated with coated pits or vesicles. Coated pits were, however, evident on the dorsal and lateral surfaces of the cell, particularly opposite the clear zone areas. Immunogold staining for clathrin confirmed that coated pits and vesicles are absent within both the clear zone and ruffled border areas, but present on the lateral and dorsal surfaces of the actively resorbing cell. It is suggested that clathrin-associated receptor-mediated endocytosis occurs along the lateral and dorsal surfaces of the osteoclast for the uptake of nutrients and macromolecules, while endocytosis of bone mineral by the ruffled border is mediated by a non-clathrin associated coated membrane structure.

Animals↗
PubMed1977

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.

Animals↗