Experimental induction of cementogenesis on the enamel of transplanted mouse tooth germs

First and second maxillary molar tooth germs with their surrounding bone were removed from 9-day-old mice, freed of the reduced enamel epithelium, re-inserted crown downwards in their bony crypts and then transplanted in the subcutaneous tissue of hosts of the same age and litter. Grafts were removed 14 days later and prepared for light and electron microscopy. In the areas where the reduced enamel epithelium was missing, a layer of cementum-like tissue was present on the enamel surface, always associated with cells showing the typical features of cementoblasts. A thin electron-lucent layer of fine fibrillar material separated the enamel surface from the new hard tissue which was composed of densely-packed collagen mixed with a ground substance. Where the cementum-like tissue was thick, cells were trapped in a collagenous matrix. The cementogenesis on enamel was strictly dependent on the absence of the reduced enamel epithelium. Thus, when exposed to follicular tissue, the surface of immature enamel appears to exert an influence on follicular cells and stimulate cementogenesis. This hypothesis could explain the presence of overgrowths of cementum in the cervical region of tooth crowns where the reduced enamel epithelium may be particularly vulnerable.

[Immunological aspects of dental transplants]

The recent literature on dental transplants in man and experimental models is reviewed. The histopathological and immunological aspects of the methods and results are critically analysed in function of the clinical applicability of this alternative to prosthesis. The different effects of mature tooth and germ transplants are considered in the light of experiments on various mammals, together with the contribution made by the various dental tissues to the taking of the transplant, and its acceptance or rejection by the host. Finally, questions associated with the establishment of a teeth bank and its potential creation of a sufficient supply of organs for transplantation are discussed.

Experimental dentigerous cysts and enamel hypoplasia: their possible significance in explaining the pathogenesis of human dentigerous cysts

Cysts lined by epithelium were often found in association with tooth-germ isografts in hamster cheek pouch. They developed from odontogenic epithelium and were in close relation to the crowns of involved teeth. Cysts associated with tooth-germ isografts from 5-day-old animals (17 out of 36) commenced their formation shortly after transplantation as a result of enamel organ degeneration. Teeth associated with these cysts often showed enamel hypoplasia. Accordingly, 86 teeth involved in human dentigerous cysts were examined and 43 were found to possess areas of enamel hypoplasia on their occlusal surfaces or incisal edges. It is suggested that the pathological process initiating cystic degeneration in the enamel organ was also accompanied by degeneration of ameloblasts. When tooth germs from 2-day-old hamsters were transplanted, cystic spaces developed only after completion of enamel formation, 6 weeks following transplantation (in six out of 11 transplants), as a result of separation between the cells of the reduced enamel epithelium. Enamel hypoplasia was not a conspicuous feature. These experimental and clinical observations suggest that there may be at least two types of dentigerous cyst, perhaps with different causes, arising at different stages of tooth development.

[Replantation and transplantation of teeth and tooth germs]

Replantation as well as the transplantation of autologous and homologous teeth or tooth buds were carries out ot utilize teeth which had been knocked out of their alveolus due to trauma and/or, if indicated, to close diastemas and aesthetically and functionally satisfactory teeth. These procedures are briefly described here and illustrated with a few cases.

The growth of the autotransplanted rat incisor tooth odontogenic organ

74 rat incisor odontogenic organs were autotransplanted intradermally into the auricle. The animals were killed in groups of four up to eight months after grafting. Out of 61 grafts examined from the third week onward, 46% exhibited a typical odontogenic organ or a well differentiated tooth with pulp, vessels and nerve fibers. In 33% only scattered epithelial islands were formed. 21% of the grafts ended as osteodentin. Following the initial trauma leading to aseptic necrosis, the most primitive odontogenic organ cells survive to generate a new tooth. The grafted odontogenic organ resumes its existence as a complex structure which mobilizes its own vascular and nervous supply from the host dermis as evident from nerve fibers which penetrated the tooth pulp. Since all original nerve fibers of the graft had to be disconnected from their cell bodies, they obviously degenerated. Thus any nerve fiber observed in the regenerating tooth pulp had to be of dermal origin.

Teeth transplanted across a multiple non-H-2 barrier stimulated weak cell-mediated immunity without memory

The genetic and immunologic criteria required for successful tooth transplantation have yet to be defined. Teeth grafted across strong barriers elicit vigorous immunity. However, teeth and tooth germs transplanted to subcutaneous sites in H-2 compatible but multiple-non-H-2 disparate recipients stimulated weak in vitro cellular cytotoxicity compared with skin grafts 5 mm in diameter. Furthermore, tooth allografts did not sensitize recipients as measured by the rejection of second-set, donor skin grafts. It may be that tooth allografts provoke fewer detrimental immune mediator systems than do skin grafts across moderate to weak transplantation barriers.

Tooth allografts fail to stimulate immunologic memory in mice

Tooth transplants should not preclude future transplants in the recipient. In this study teeth failed to stimulate immunologic memory in weakly disparate mice. The teeth did carry transplantation antigens and were rejected after second-set skin grafts. The teeth probably enhanced their own survival through some immunoregulatory mechanism.

Transplantation of bovine odontogenic tissues and dissociated odontogenic cells to hypothymic mice

It was demonstrated in this study that bovine odontogenic tissues and the dissociated cell preparations of such tissues, when transplated to the subcapsular kidney site of hypothymic mice, retained their phenotypic expression and continued function to produce their recognisable products, dentine and enamel matrices. It was also shown that in the grafts of dissociated odontogenic tissues, cell sorting occurred so that histotypical tissues were formed and that their function produced readily recognisable dentine and enamel matrices. Attention has been drawn to the usefulness of this model for studying a variety of events that occur during odontogenesis.

Experimental isografts of odontogenic tissues

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