Development of a gomphosis by tooth germ implants in the parietal bone of the mouse

Development and cell fate in interspecific (Mus musculus/Mus caroli) orthotopic transplants of mouse molar tooth germs detected by in situ hybridization

Interpretation of results from previous tooth germ transplantation studies is limited by the inability to distinguish between donor and host cells unequivocally. Furthermore, ectopic transplantation sites have generally been used and the relevance of this to tooth development in situ is uncertain. The aim here was to determine cell fate in orthotopic tooth germ transplants using an interspecific mouse marker system. Mandibular first molar tooth germs were dissected from Mus musculus (CD1) and Mus caroli mice (age range 15-19 day embryo) and transplanted interspecifically into the alveolar crypt of extirpated first mandibular molars in neonatal M. musculus (CD1) and M. caroli hosts. Grafts were recovered at intervals up to 4 weeks postoperatively. Paraffin wax-embedded sections were examined using routine histological techniques and in situ hybridization with a biotinylated DNA probe (pmSat5) specific for M. musculus, to distinguish between donor and host cells. Development of M. musculus tooth germs in M. caroli mandibles and vice versa was similar and transplants progressed to incipient root formation. Vascularization of transplants was chimaeric, being donor-derived in the pulp and host-derived more peripherally. The investing soft tissues comprised a mixture of donor and host cells, predominantly donor. Donor cells were also found in the soft tissue of intertrabecular spaces in the surrounding bone, but alveolar osteocytes were almost entirely host-derived. Long-term survival of grafts was limited and few donor cells were present after 2 weeks. This study provides an unequivocal demonstration of the origin of all cells present in transplanted tooth germs.

Periodontal regeneration in a buccal dehiscence model in monkeys after application of enamel matrix proteins

There is increasing evidence that cells of the epithelial root sheath synthesize enamel matrix proteins and that these proteins play a fundamental role in the formation of acellular cementum, the key tissue in the development of a functional periodontium. The purpose of the present study was to explore the effect of locally applied enamel matrix and different protein fractions of the matrix on periodontal regeneration in a buccal dehiscence model in monkeys. Buccal, mucoperiosteal flaps were raised from the canine to the 1st molar on each side of the maxilla. The buccal alveolar bone plate, the exposed periodontal ligament and cementum were removed. Various preparations of porcine enamel matrix with or without vehicles were applied before the flaps were repositioned and sutured. After 8 weeks, the healing was evaluated in the light microscope, and morphometric comparisons were made. Application of homogenized enamel matrix or an acidic extract of the matrix containing the hydrophobic, low molecular weight proteins, amelogenins, resulted in an almost complete regeneration of acellular cementum, firmly attached to the dentin and with collagenous fibers extending over to newly formed alveolar bone. After application of fractions obtained by neutral EDTA extraction containing the acidic, high molecular weight proteins of the enamel matrix, very little new cementum was formed and hardly any new bone. The results of the controls in which no test substance was applied before the repositioning of the flap, were very similar to those obtained with the EDTA extracted material. Propylene glycol alginate (PGA), hydroxyethyl cellulose and dextran were tried as vehicles for the enamel matrix preparations. Only PGA in combination with the amelogenin fraction resulted in significant regeneration of the periodontal tissues.

Cementogenesis reviewed: a comparison between human premolars and rodent molars

BACKGROUND

Cementum continues to be the least-known mineralized tissue. Although recent advances in the field of molecular biology have contributed to an understanding of the involvement of molecular factors in cementum formation during development and regeneration, cementogenesis on a cell biological basis is still poorly understood. Virtually nothing is known about cementoblast origin, differentiation, and the cell dynamics during normal development, repair, and regeneration. This review describes the recent findings of cementogenesis on roots of human premolars and opposes them to those of teeth from other mammals, particularly the rodent molar.

METHODS

Using light and electron microscopy, light microscopic radioautography, and various measurements, a comprehensive insight into the development and repair of cementum during and after root formation and tooth eruption has been achieved for human premolars.

RESULTS

Cementum is a highly responsive mineralized tissue. This biological activity is necessary for root integrity and for bringing and maintaining the tooth in its proper position. With regard to cementum formation and periodontal fiber attachment, considerable species-particularities exist that are mainly based on differences in growth rates and tooth sizes. Since root development and initial cementogenesis last on the average 5-7 years in human premolars, cementum formation in these teeth is characterized by along-lasting phase of prefunctional development, with occurs independent of principal periodontal fiber attachment to the root and which may take 5 years or more. The first molar of the rat, however, is in functional occlusion 3 1/2 weeks after the onset of root formation. Since initial cementum formation and periodontal fiber attachment to the root occur almost at the same time in this tooth, the distinction between cells associated with one or the other process is very difficult to achieve, and cementogenesis cannot be described independent of periodontal fiber attachment to the root. Therefore, the determination of cementoblast origin in the rodent molar may be intricate.

CONCLUSIONS

Taking into account these species differences, the current description on the origin and differentiation of cementoblasts is inconsistent and the description of cementogenesis is still incomplete. This review calls into question the currently held concept of cementogenesis and offers a possible alternative.

Development and cell fate in interspecific (Mus musculus/Mus caroli) intraocular transplants of mouse molar tooth-germ tissues detected by in situ hybridization

Mandibular first molar tooth germs were dissected from Mus musculus (CDI) and Mus caroli (age range: 14-day embryo to 1-day postnatal). Most of the tooth germs were separated enzymically into epithelial and mesenchymal components. Interspecific tissue recombinations and intact M. caroli tooth germs were grown in the anterior chamber of the eye of adult CDI mice for 24 weeks. Recombinations of M. caroli enamel-organ epithelium with M. musculus, dental papilla and follicle mesenchyme developed into normal teeth with advanced root, periodontal ligament and bone formation, thereby confirming extensive epithelial-mesenchymal interactions across the species barrier. Labelling sections by in situ hybridization with a M. musculus-specific DNA probe (pMSat5) showed that almost all cells in the pulp, periodontal ligament and bone were M. musculus, including cementoblasts. Reduced enamel epithelium and epithelial cell rests derived from donor M. caroli enamel organ were unlabelled. This indicates that any cementogenic role of Hertwig's epithelial root sheath must be short-lived. The immunological privilege of the intraocular transplantation site in M. musculus CDI mice did not extend to grafts including xenogeneic M. caroli dental mesenchyme. Thus, intact M. caroli tooth germs and recombinations of M. musculus enamel organ with M. caroli dental papilla and follicle showed limited development, with no root formation, and were populated almost exclusively with labelled host M. musculus lymphocytes.

A comparative investigation on autologous mandibular and iliac crest bone grafts. An experimental study in sheep

Nine Friesian sheep (age 1.5-2 years) were used to evaluate the quality of bone repair in artificial cleft-like maxillary defects repaired with autologous bone grafts of embryologically different origin. After bilateral extraction of the upper first deciduous molar the tooth socket was enlarged resulting in an open connection between the oral and nasal cavities. In the same session a graft, obtained from the iliac crest, was implanted in one of the two bilateral maxillary defects and on the opposite side a graft, obtained from the mandible, was inserted. During the experiment, serial radiographs were taken. After six months the sheep were sacrificed and the bone of the grafted areas was submitted to histological and histomorphometric investigation. Comparing both areas, it appeared that the quality of bone remodelling and alveolar reconstruction was independent of the origin of the grafts.

An autoradiographic study of periodontal development in the mouse

Tritiated thymidine was injected into 10- and 13-day-old mice because at this age the third molar is at the appropriate stage of development. At set intervals, the mice were killed and the distribution of labeled cells within the dental papilla and follicle examined. The change in labeling index with time was measured for defined areas in the papilla and follicle. It was shown that, during the late bell stage of development, cells moved from the papilla into the follicle. It was concluded that the pulp, rather than the investing layer of the follicle, is the source of the periodontium and that growth of the pulp and periodontal tissues could generate an important force contributing to tooth eruption.

Dental structures in benign ovarian cystic teratomas (dermoid cysts). A study of ten cases with a review of the literature

Tooth-forming ovarian teratomas provide a unique opportunity to observe the effect(s) of the tumor environment on developing dental structures. Histologic examination of two such teratomas showed essentially normal formation of dental structures in one and pronouncedly aberrant morphodifferentiation of dental tissues in the other. The macroscopic examination of a total of twenty-five teeth from eight additional teratomas showed most teeth to have premolar or molar forms. Most teeth were not distinctly deciduous or permanent but had intermediate shapes. The teeth within a tumor tended not to form normal morphologic sequences. It is concluded that dental structures in ovarian teratomas are products of normal genetic/epigenetic events modified to a greater or lesser degree by unknown factors in the tumor environment.

Augmentation of tooth and jaw regeneration in the frog with a digital transplant

Augmentation of a regeneration site in the maxilla of the frog with a digital transplant resulted in an earlier bony union but did not affect the rate of regeneration of teeth which still ankylosed to a separately induced bony base rather than to the transplanted digital bone.

Tooth eruption: evidence for the central role of the dental follicle

The roles of the gubernaculum dentis, root formation, tooth crown and dental follicle in prefunctional eruption of a mandibular premolar have been studied in nine beagle dogs by radiographic and histologic evaluations of the effects of surgical ablation or removal of these structures on tooth eruption. The dental follicle was the only one of these structures required for the coordinated enlargement of the eruption pathway and formation of bone in the base of the bony crypt, the radiographic and histologic hallmarks of tooth eruption. These data, together with the topographic relationships of the dental follicle to areas of localized bone resorption and formation, are interpreted to mean that the dental follicle may influence, if not coordinate, these processes in tooth eruption.