Application of induced pluripotent stem cells in generation of a tissue-engineered tooth-like structure

Stem cells, such as adult stem cells or embryonic stem cells, are the most important seed cells employed in tooth tissue engineering. Even though dental-derived stem cells are a good source of seed cells for such procedures, they are not often used in clinical applications because of the limited supply. Induced pluripotent stem (iPS) cells, with their high proliferation and differentiation ability, are now considered a promising alternative. The objectives of this study were to assess the role of iPS cells in tooth tissue engineering. We used real-time polymerase chain reaction to confirm that mouse iPS (miPS) cells can be induced to express both odontogenic and osteogenic gene profiles. We then established a tooth germ model and transplanted the recombinant tooth germ into a mouse subrenal capsule for 4 weeks to reproduce early-tooth organogenesis. After 4 weeks, hematoxylin and eosin staining results showed newly formed bone-like and dental pulp-like areas. Further immunohistochemical staining confirmed that osteopontin was present in the apical part of the tooth-like structure. These results demonstrate that miPS cells have the potential to differentiate into odontogenic cells, confirming that they could be a new source of seed cells for use in tooth tissue engineering.

Whole-tooth regeneration: it takes a village of scientists, clinicians, and patients

A team of senior scientists was formed in 2006 to create a blueprint for the regeneration of whole human teeth along with all of the supporting structure of the dentition. The team included experts from diverse fields, each with a reputation for stellar accomplishment. Participants attacked the scientific issues of tooth regeneration but, more importantly, each agreed to work collaboratively with experts from other disciplines to form a learning organization. A commitment to learn from one another produced a unique interdisciplinary and multidisciplinary team. Inspired by the Kennedy space program to send a man to the moon, with its myriad of problems and solutions that no one discipline could solve, this tooth regeneration team devised an ambitious plan that sought to use stem cell biology, engineering, and computational biology to replicate the developmental program for odontogenesis. In this manner, team members envisioned a solution that consisted of known or knowable fundamentals. They proposed a laboratory-grown tooth rudiment that would be capable of executing the complete program for odontogenesis when transplanted to a suitable host, recreating all of the dental tissues, periodontal ligament, cementum, and alveolar bone associated with the canonical tooth. This plan was designed to bring regenerative medicine fully into the dental surgery suite, although a lack of funding has so far prevented the plan from being carried out.

[Experimental study on the development of tissue-engineered tooth germ with heterotopic allotransplantation]

OBJECTIVE

To compare the growth and development of tissue engineered tooth germ implanted into different tissues, and explore a suitable growing environment for the tissue engineered teeth in vivo.

METHODS

SD rat/porcine tooth germ cells from postnatal 4 days were used as seeding cells, which combined various scaffolding biomaterials to construct the compound with tissue engineered teeth. The allografts were implanted into renal subcapsule, the mesenteries and subcutaneous tissues. Then, the implants were retrieved at special time points for histological analysis.

RESULTS

Further developments were not observed in the graft implanted into mesenteries and subcutaneous tissues. Partial grafts were fallen off and lost from the subcutaneous tissues after implanted, and there were obvious lymphocyte infiltrations in the mesenteries. Moreover, the enamel and pulp-dentin complex were observed within the graft implanted in the subrenal capsule, which indicated there to be good condition.

CONCLUSION

The subrenal capsule can provide a promising implantation environment for the further growth of allogeneic tissue engineered tooth germ, and the subrenal capsule implantation can be used as a new alternative method for tissue-engineering tooth in vivo.

Regulating the Role of Bone Morphogenetic Protein 4 in Tooth Bioengineering

PURPOSE

Culture of the whole organ and regulation of its development using biologic and engineering principles can be used to produce structures and organs for reconstructing defects. The application of these bioengineering approaches in artificial tooth development may be the alternative way to replace missing dentition.

MATERIALS AND METHODS

For the artificial bioengineering of a mouse tooth, tooth buds were dissected and transplanted into the diastema of the developing mandible. The mandiblular primordia containing transplanted tooth buds were culture in vitro and in vivo using a bioengineering method. In addition, to regulate the development of tooth germs, bone morphogenetic protein 4 (BMP4) or its antagonist, Noggin was administered.

RESULTS

After the period of in vitro and in vivo culture, the transplanted tooth germ in the diastema showed tooth development with supportive structure formation. In the BMP-treated group, the bioengineered tooth was observed with increased maturation of cusp and enamel matrix. However, in the Noggin-treated tooth germs, the developing molar had a crater-like appearance with the immature development of the cusp and suppressed formation of the enamel matrix.

CONCLUSIONS

This study confirmed that tooth germ transplantation in the diastema and culture with administration of BMP4 could lead to the mature development of the dental structures. In addition, these results suggest the possibility of bioengineering the tooth in morphogenesis and differentiation even in the toothless area.

Inhibition of apoptosis in early tooth development alters tooth shape and size

Apoptosis plays important roles in various stages of organogenesis. In this study, we hypothesized that apoptosis would play an important role in tooth morphogenesis. We examined the role of apoptosis in early tooth development by using a caspase inhibitor, z-VAD-fmk, concomitant with in vitro organ culture and tooth germ transplantation into the kidney capsule. Inhibition of apoptosis at the early cap stage did not disrupt the cell proliferation level when compared with controls. However, the macroscopic morphology of mice molar teeth exhibited dramatic alterations after the inhibition of apoptosis. Crown height was reduced, and mesiodistal diameter was increased in a concentration-dependent manner with z-VAD-fmk treatment. Overall, apoptosis in the enamel knot would be necessary for the proper formation of molar teeth, including appropriate shape and size.

[A histological innovative study of Balb/c mouse tooth germ transplanted to nude mouse in vivo]

PURPOSE

To observed the changes of the developed mouse's dental germs after transplanting into nude mouse and find some theoretical foundation for establishing an innovative experimental model.

METHODS

Eight tooth germs from four 5th day postnatal Balb/c mice were transplanted to the back muscles of the adult nude mice. At seventh and fourteenth day after grafting, the germs were collected, fixed, demineralized, dehydrated, and embedded in wax. Serial sections of 5 microm thick were made following the routine methods, stained with haematoxylin-eosin dying solution, and observed under a light microscope. The mandibular first molars were taken out from the 12th and 19th day postnatal mouse. Serial sections of 5 microm thick were made following the routine methods, then compared with the germs after graft.

RESULTS

All implantations were located in the superficial muscles with abundant capillary vessels. The dental germs could further developed after grafting under the microscope, but slower than dental germs self-development. The layer of dentin was thin, plenty of dentin with disorganized dentin tubule formed after grafting. Although the location of Hertwig's epithelial root sheath hardly moved, the roots developed further. The floor of pulp chamber could form and the pulp chambers were shrinking. The degree of calcification in the area of root increased very clearly. The inflammatory reaction was found at 7th day while hardly noted at 14th day after grafting.

CONCLUSIONS

It suggests that late development of mouse tooth germs could further develop after heterotopic transplantation within the superficial muscles of the nude mouse. This model is useful for study of tooth root development in short time.

Bioengineered teeth from tooth bud cells

Advances in tissue engineering and materials science have led to significant progress in hard and soft tissue repair and regeneration. Studies demonstrate the successful application of tissue engineering for bioengineering dental tissues. The ability to apply tissue engineering to repair or regenerate dental tissues and even whole teeth is becoming a reality. Current efforts focus on directing the formation of bioengineered dental tissues and whole teeth of predetermined size and shape. Advances in dental progenitor cell characterizations, combined with improved methods of fabricating biodegradable scaffold materials, bring closer the goal of making tooth tissue engineering a clinically relevant practice.

Preliminary Study of Tissue-Engineered Odontogenesis in the Canine Jaw

PURPOSE

We previously reported a method for the development of tissue-engineered tooth. However, 1 drawback of the procedure was the inability to determine whether the tooth would function when transplanted in the jaw because it was formed in the omentum of the abdomen. Therefore, the present study was designed to evaluate whether transplantation of dissociated odontogenic cells could induce tissue-engineered odontogenesis in the canine jaw.

MATERIALS AND METHODS

Cells were harvested from canine first molar tooth buds and the resulting heterogeneous cell population was seeded on a biodegradable polymer. These constructs were then transplanted into the same sockets after extracting the tooth buds. After transplantation, we evaluated the transplanted constructs using dental x-ray, micro-computed tomography, histology, and immunohistochemistry.

RESULTS

After 24 weeks, micro-x-ray computed tomography showed regenerated hard tissues in the jaw, and hematoxylin and eosin staining showed tubular dentin and bone. In the regenerated tissue, osteopontin, osteonectin, and osteocalcin antibodies stained the dentinal matrix. However, enamel tissue and dental-root formation were not observed.

CONCLUSION

These data show for the first time the formation of dentin and bone from dissociated odontogenic cells in the canine jaw.

Tissue-engineered hybrid tooth and bone

Tooth loss accompanied by alveolar bone resorption presents a significant clinical problem. We have investigated the utility of a tissue-engineering approach to provide corrective therapies for tooth-bone loss. Hybrid tooth-bone tissues were bioengineered as follows. Tooth implants were generated from pig third molar tooth bud cells seeded onto polyglycolide (PGA) and polyglycolide-colactide (PLGA) scaffolds, and grown for 4 weeks in the omenta of adult rat hosts. Bone implants were generated from osteoblasts induced from bone marrow progenitor cells obtained from the same pig, seeded onto PLGA fused wafer scaffolds, and grown for 10 days in a rotational oxygen-permeable bioreactor system. The tooth and bone implants were harvested, sutured together, reimplanted, and grown in the omenta for an additional 8 weeks. Histological and immunohistochemical analyses of the excised hybrid tooth-bone constructs revealed the presence of tooth tissues, including primary and reparative dentin and enamel in the tooth portion of hybrid tooth-bone implants, and osteocalcin and bone sialoprotein-positive bone in the bone portion of hybrid tooth-bone constructs. Collagen type III-positive connective tissue resembling periodontal ligament and tooth root structures were present at the interface of bioengineered tooth and bone tissues. These results demonstrate the utility of a hybrid tooth-bone tissue-engineering approach for the eventual clinical treatment of tooth loss accompanied by alveolar bone resorption.

Autotransplantation of immature third molars into edentulous and atrophied jaw sections

The aim of the present study was to assess the results after transplantation of 85 immature third molars. Recipient site conditions varied and different surgical techniques were used. The long-term results after preparation of a new alveolus, splitting osteotomy of the alveolar process or use of free bone autografts were compared with the results after transplantation into a fresh extraction site (control group). Transplantations into prepared sockets showed equal results to the control group (94% respectively). Transplantations in connection with free bone autografts (84%) or after splitting osteotomy of the alveolar process (63%) showed poorer success rates, the differences between the latter and the control group being statistically significant. A possible correlation to revascularization disturbances of the pulp due to an insufficiency of the recipient site or to postoperative infection is suspected. The results show that transplantation of immature third molars is a safe, useful procedure when appropriate conditions of the recipient site are present. Where the alveolus is atrophic, a splitting osteotomy should be performed only in exceptional cases and preference should be given to alternative methods such as primary bone augmentation or bone-regenerative procedures.

Bioengineered teeth from cultured rat tooth bud cells

The recent bioengineering of complex tooth structures from pig tooth bud tissues suggests the potential for the regeneration of mammalian dental tissues. We have improved tooth bioengineering methods by comparing the utility of cultured rat tooth bud cells obtained from three- to seven-day post-natal (dpn) rats for tooth-tissue-engineering applications. Cell-seeded biodegradable scaffolds were grown in the omenta of adult rat hosts for 12 wks, then harvested. Analyses of 12-week implant tissues demonstrated that dissociated 4-dpn rat tooth bud cells seeded for 1 hr onto PGA or PLGA scaffolds generated bioengineered tooth tissues most reliably. We conclude that tooth-tissue-engineering methods can be used to generate both pig and rat tooth tissues. Furthermore, our ability to bioengineer tooth structures from cultured tooth bud cells suggests that dental epithelial and mesenchymal stem cells can be maintained in vitro for at least 6 days.

Development of tooth germ heterotopically grafted within the ear skin. An histological study in the rat

The main goal of this study was the analysis of the developmental potentiality of tooth germ from late bell stage on, after its heterotopic placement within the skin. Teeth germs of newborn rats were grafted within a skin pouch of the ear of adult rats. Seven to fourteen days after grafting, dental germs developed normal dental structures in which ameloblasts and odontoblasts were well differentiated. Twenty to forty-one days after graft, the inflammatory host reaction destroyed the dental developed tissues by cell infiltration. The dentin of the grafts was of osteoid characteristics, and its size increased depending on grafting time until the complete substitution of all dental tissues. This atypical dentin showed several degrees of polymerisation from collagen fibres smooth dentin devoid near the graft a to fibres rich dentin far from the dental germ. Present results suggest that this type of dental graft could be a valuable model to study the self-development of dental tissues and the reactive mechanisms taking place after dental injuries.

Influence of aging on tooth eruption: experimental canine mandibular allograft

PURPOSE

Aging is clinically related to tooth eruption; however, there are no known studies that have elucidated the relationship. We examined whether tooth eruption would occur normally in a mature subject.

MATERIALS AND METHODS

Using vascularized composite tissue mandibular transplantation, we extracted portions of immature mandibles including the tooth germs from young beagle dogs and placed them into unrelated immature and mature beagle dogs. We then examined eruption of the lower first molar in the grafted mandibular bone and compared the results clinically, radiographically, and histologically.

RESULTS

Normal tooth eruption was observed in the transplanted mandibles in the young dogs. In the mature dogs, eruption from the gingiva was delayed, whereas that from alveolar bone occurred normally in the transplanted mandibles. Further, the whole crown was covered with a cap of gingival tissue in the mature dogs, although this cap was not gingival overgrowth.

CONCLUSIONS

Tooth eruption is influenced by some unknown factors related to aging. Apparently, apoptosis did not occur in the connective tissues between the reduced enamel epithelia and oral epithelia that overlay the teeth in the mature subjects.

Lineage of non-cranial neural crest cell in the dental mesenchyme: using a lacZ reporter gene during early tooth development

The tooth is one of the ectodermal organs controlled by reciprocal interactions between the epithelium and the mesenchyme. Mesenchymal cells in the developing tooth, so-called dental mesenchymal cells, are derived from two different origins: the cranial neural crest (CNC) and the non-CNC. These CNC-derived cells migrate, proliferate and differentiate into odontoblasts, cementoblasts, fibroblasts, osteoblasts and chondroblasts. Tooth germs of wild-type mice were transplanted into the kidney of adult lacZ-transgenic mice. After 1 week of transplantation, a few lacZ-expressing cells and many red blood cells were found near or inside the blood vessels in the pulp of wild-type tooth germs. This result shows that circulating cells of the adult host could invade the dental pulp during tooth development, through the blood vessels, and be a part of dental pulp tissue. Therefore, it can be suggested that these circulating progenitor cells could be the origin of non-CNC-derived cells in tooth germ and their migration pathways would be the blood vessels invading the dental pulp during tooth development. If variations of this experiment were suitably adjusted, such as the embryonic stage of the tooth germ, duration of transplantation, etc., this transplantation experiment using adult lacZ-transgenic mice could be a good system to reveal the origin and migration pathway of cells in developing organs as well as in dental mesenchymal cells.

[Tooth transplantation]

Tooth transplantations provide the option of replacing lost or missing teeth in a biological fashion. On account of their high success rates and primarily in Scandinavian countries, they are a popular alternative to orthodontic or prosthetic treatment--particularly in case of children or young people losing teeth in accidents. Success of the treatment is ensured by corresponding diagnosis and good preoperative planning. Tissue-conserving transplant collection and the corresponding conditioning of the transplant bed are of decisive importance for the regeneration of the pulp and the periodontium. The success of the therapy is also influenced by the type and duration of splinting. Depending on the surgical technique and the transplanted tooth, the success rates are between 78% and 96%. The success criteria of a transplantation are defined clinically and radiologically. The diagnosis for transplantation is made from an orthodontic, endodontic, traumatologic, periodontologic and cardiologic perspective. The present article provides an overview of literature and shows current plantation techniques.

Functional fixation of autotransplanted tooth germs by using bioresorbable membranes

OBJECTIVE

The purpose of this study was to evaluate the contribution of a bioresorbable membrane placement to the healing of immature teeth after autotransplantation of tooth buds.

STUDY DESIGN

Six cases were selected: 2 transplantations of wisdom teeth, 2 for premolar agenesis, 1 for ectopia, and 1 premolar in an incisor position. The crown of each tooth germ and the marginal alveolar bone were covered with a resorbable membrane.

RESULTS

The radicular edification was nearly complete, neither ankylosis nor inflammatory resorption was observable, the pulp vitality was preserved, and the periodontal integration was identical to that of other teeth. The membrane ensured contention and stabilization of the transplant, allowed functional stimulation, permitted protection of the coagulum and periodontal cells, and kept the epithelium at a distance.

CONCLUSIONS

The transplantations of immature teeth were improved by the use of a resorbable membrane, which caused an optimal functional fixation of the transplanted tooth.

Autotransplantation of immature third molars: influence of different splinting methods and fixation periods

Different data were published documenting the influence of fixation methods and periods on the outcome of autotransplantations of teeth. Besides studies reporting increased ankylosis and disturbances of pulpal revascularization following rigid or extended fixation, there are studies revealing no connection in this matter. The clinical and radiological results of 76 transplanted germs of third molars were to be assessed after a rigid fixation for 4 weeks or after a suture splinting for 7 days and compared with each other. The choice of fixation method depended on the initial stability of the transplant. After a mean observation period of 3.4 years (range 1.0-6.1 years), 92.9% of the teeth stabilized with a suture, but only 73.5% fixed with an acid-etch composite and wire splint could be classified as successful (P = 0.029). The significant increases in ankylosis (P = 0.036) and pulp necrosis (P = 0.041) were the factors for the less favorable results of the rigidly fixed teeth. Our data support the results of other experimental and clinical studies with regard to the negative influences of an extended and rigid fixation on the success of tooth transplantation. However, apart from a correlation with the method and period of fixation, we also suspect the influence of an incongruity between the transplant and recipient site.

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.

Experimental odontogenic cysts induced by in vitro 4-nitroquinoline 1-oxide (4NQO) treatment of F344 rat incisor tooth germs

This study was designed to establish an experimental animal model for elucidating the early stages of odontogenic cysts and tumors. It involves the in vitro treatment of tooth germs with 4-nitroquinoline 1-oxide (4NQO) at the early bell stage and their subsequent transplantation into the kidney subcapsular space. While all tooth germ transplants of the control group not exposed to the carcinogen showed continued tooth development with no pathological lesions, 21 of 23 4NQO-treated tooth germs developed into similar appearing keratinized cysts with or without associated tooth structures. The remaining two transplants failed to develop cysts and formed only a tooth. The present experimental procedure was effective in inducing keratinized cystic lesions that exhibit some similarities to human odontogenic keratocysts or primordial cysts.

[Auto-transplantation of tooth germs. Discussion and presentation of 3 treated cases]

The authors examine the theoretical possibilities of human dental transplants: autologous, homologous and heterologous. They, then discuss-with reference to autologous transplants-an autotransplant as an alternative to prosthodontic treatment. This would apply both to traditional prosthodontic treatment and on implants or orthodontic treatment aiming at filling dental gaps. They show both general and local counterindications against this operational method the knowledge of which is necessary for an adequate selection of patients. They stress the determining factors for a successful autotransplant: 1) particular care with the choice of the germ to be transplanted taking into account its morphology and the stage of root development; 2) adequate surgical preparation of the receiving site in relation to the size of the germ to be transplanted; 3) suitable surgical technique entailing a particular care in the manipulation of soft and hard tissues and of the germ and appropriate conditions of sterilization; 4) use of appropriate retention means to ensure stability of the transplanted germ so as to favour cellular proliferation and reduce osteoclastic activity; 5) reduction of occlusal pressure on the transplanted germ. The authors describe for example's sake 3 out of 32 cases treated with the documentation of the achieved long-term success. They also analyse the possible causes of failure of such operational method (careless manipulation of the germ, incorrect surgical technique, removal of the germ in a too early stage of its development, too long exposure of the germ outside the oral cavity, poor oral hygiene, caries, periodontal disease, occlusal trauma.

Premolar child-to-parent grafting within the framework of orthodontic serial extraction

While allografting of human teeth holds all the risks and problems of immunological reactions or host-versus-graft reactions encountered in any organ transplantation, root resorption and thus the loss of the grafted tooth may be delayed by several decades if the transfer is between close relatives and minimum histocompatibility is 50%. In 2 cases premolars with incomplete root growth, which had to be extracted because of considerable crowding, were transplanted from child to mother and child to father, respectively. The grafts healed without complications and after a retention time of several weeks the teeth were attached. Three years after transplantation the teeth show only minor signs of root resorption and are fully functional.

Long-term histopathologic findings in tooth germs autotransplantation. Analysis of a series

Tooth germ autotransplantation, a surgical technique based upon extraction of a germ followed by reimplantation in the same individual, is indicated in tooth agenesis or loss as an alternative to traditional methods of treatment. The success of autotransplantation relies on several factors, and clinical studies indicate that results are excellent if correct surgery is carried out. This work offers a morphological contribution to the understanding of post-transplantation changes of the pulp, periodontal ligament and root cementum.

Polarizing activity, Sonic hedgehog, and tooth development in embryonic and postnatal mouse

Tooth development involves reciprocal epithelial-mesenchymal interactions, polarized growth, mesenchyme condensation, and complex morphogenetic events. Because these processes bear similarities to those occurring in the developing limb, we asked whether morphogenetic signals found in the limb also occur in the developing tooth. We grafted mouse embryo tooth germs to the anterior margin of host chick embryo wing buds and determined whether the dental tissues had polarizing activity. Indeed, the grafts induced supernumerary digits. Activity of both molar and incisor tooth germs increased from bud to cap stages and was maximal at late bell stage in newborn. With further development the polarizing activity began to decrease, became undetectable in adult molar mesenchyme but persisted in incisor mesenchyme, correlating with the fact that incisors grow throughout postnatal life while molars do not. When different portions of neonatal incisors were assayed, a clear proximo-distal gradient of activity was apparent, with maximal activity restricted to the most proximal portion where undifferentiated mesenchyme and enamel organ reside. In situ hybridizations demonstrated that prior to induction of supernumerary digits, the tooth germ grafts induced expression in host tissue of Hoxd-12 and Hoxd-13. In addition, whole-mount in situ hybridizations and immunohistochemistry showed that developing tooth germs express Sonic hedgehog (Shh). Shh expression was first detected in bud stage tooth germs; at later stages Shh transcripts were prominent in enamel knot and differentiating ameloblasts at the cuspal region. We concluded that tooth germs possess polarizing activity and produce polarizing factors such as Shh. As in the limb, these factor(s) and activity probably play key roles in establishing polarity and regulating morphogenesis during early tooth development. Given its subsequent association with differentiating ameloblasts, Shh probably participates also in cytogenetic events during odontogenesis.

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.

[Outcome of wisdom tooth germ transplantation]

In 68 patients, 79 tooth germs of the third molar were transplanted. Out of this group, 43 patients with 50 transplantations under-went a follow-up examination. All surgery was performed by one surgeon. Retrospectively, we tried to establish whether the success of postoperative healing depends on the donor and receiver regions. Crossing the jaw border clearly worsens the prognosis for transplantation. Altogether 9 transplantations turned out to be failures, 7 of which had been transplanted from the upper to the lower jaw. The results of this investigation showed incomplete root development in 34%, the necessity of endodontic treatment in 6% and enlarged periodontal pockets in 8%. Ankylosed teeth were found in 10%; we did not see any root resorptions.

Autotransplantation of teeth in cases with agenesis or traumatic loss of maxillary incisors

The purpose of this study was to investigate the prognosis of 50 consecutively autotransplanted teeth to the maxillary incisor region. Thirty-five were transplanted in cases of traumatic injuries, eleven in cases of agenesis and four in cases with impaction of maxillary canines. The average follow-up time was 7 years and 6 months (range 4-17 years). The transplants were examined clinically in respect of tooth vitality and radiographically in respect of root canal obliteration, periradicular changes, root formation, and root length. The results show a success rate of 82 per cent. It is concluded that the procedure of tooth transplantation has the advantage of maintaining or restoring alveolar bone volume and gives the opportunity to replace a missing tooth without involvement of neighbouring teeth as prosthetic abutments.

[The possibility of orthodontic therapy in transplanted teeth]

The paper reports four cases of tooth transplant: two teeth were transplanted once they were fully mature (completely formed roots) and two were transplanted as germs. Having documented the clinical and radiological recovery for all four teeth, orthodontic braces were applied for a variety of reasons. In the two cases of teeth transplanted once the roots had completely formed it was impossible to move the teeth, whereas in the case of the germ transplants the teeth were quickly moved to a correct occlusal position. On the basis of these different reactions, the author assesses the possibility of histological recovery of the tooth transplant. Repeated radiographic controls showed anomalies in radicular formation and of the camera pulposa. Lastly, the paper discusses the optimal time to transplant a tooth germ.

[Tooth germ transplantation or gap closure--a comparative study in the loss of the first molar]

In our study 37 transplanted and 33 mesialized molars by orthodontics were clinically and radiologically compared. The teeth moved by orthodontics showed a better long-term prognosis. As vital teeth with functioning periodontal structures and only slightly shortened roots they were equivalent to healthy teeth. However, the disadvantage of orthodontic space closure is the requirement of a good compliance due to long treatment time. The prognosis of maintaining a transplanted tooth germ is uncertain. One third of the teeth showed an altered periodontium with resorption areas. The danger of a continuing resorption, as well as a late external resorption is still a risk after a long period of time and can eventually lead to tooth loss. As a treatment alternative, germ transplantation may serve as a replacement of a single missing 6-year-molar in adolescence. Orthodontic space closure is indicated at any age with an existing dysgnathia, the loss of several first molars, the loss of space and mesial tipping of the second molars.

Repair potential in localized juvenile periodontitis. A case in point

An aggressive form of localized juvenile periodontitis (LJP) in a 12-year old West African female is reported. The case was treated with scaling, root planing, debridement, and tetracycline therapy, which resulted in complete resolution of the disease, including elimination of periodontal inflammation, regeneration of lost periodontal structures, and spontaneous repositioning of teeth that had pathologically migrated. A hopelessly involved mandibular right first molar was successfully replaced by an incompletely developed maxillary third molar tooth bud whose roots and pulp structure continued to develop after autotransplantation. It is suggested, that LJP can be successfully treated without periodontal surgery and that the potential for repair in LJP cases is apparently greater than what one can anticipate in adult forms of periodontitis.

Calcification capacity of dental papilla mesenchymal cells transplanted in the isogenic mouse spleen

The capacity of the dental pulp to form calcified tissue was examined in papilla cells dissociated from first molar tooth germs of the neonatal mouse and isografted in the spleen for up to 7 days. To obtain papilla cell populations without odontoblasts, pulpal mesenchyme was isolated mechanically from the enamel organ after 0.1% trypsin treatment and rolled on a membrane filter. On day 3 after transplantation, the grafted papilla cells had changed into large, spindle-shaped cells, and initial calcification with needle-like crystals began in association with the collagenous matrix surrounding those cells. On day 7 after transplantation, the spindle cells transformed into odontoblast-like cells containing well-developed secretory organelles, and irregular, but nontubular, calcified tissues were commonly observed surrounding the extracellular collagenous matrix. The calcified tissue matrix with cellular inclusions displayed a structure similar to that of osteodentin. During this period, an intense positive reaction for alkaline phosphatase (ALPase) activity was demonstrated along the cell membranes of the odontoblast-like cells aligned at the periphery of forming calcified tissue. Enzymatic activity could not be detected on the cells incorporated completely into osteodentin-like matrix. The present results show that the papilla cell population transplanted into the spleen formed osteodentin-like material, thus demonstrating the capacity of papilla cells to produce calcified tissue.

Creation of a chimaeric periodontium in the rat by isotopic tooth germ transplantation

The purpose of this work was to develop and test a chimaeric periodontium in which it would be possible to distinguish between connective tissue cells of odontogenic and oral mucosal origin. The recombinant periodontium was created by transplanting first maxillary molar tooth germs with their follicles from 1-3-day-old hooded Lister rats into the corresponding evacuated crypts of 6-9-day-old histocompatible recipients of the same strain. Of 71 transplants, 22 had formed erupted teeth 3 weeks later, with dentogingival junctions and periodontal ligaments histologically similar to those of control teeth. The recombinant nature of the graft periodontium was confirmed by incubating tooth germs in vitro with tritiated thymidine before grafting them, and then demonstrating radiolabelled nuclei in the dentogingival junctions formed by the transplants. Labelled cells were randomly distributed within the periodontal ligament and predominantly near to the basement membrane of junctional epithelium.

[Autotransplantation of tooth germs]

During the routine orthodontic examination of a 8-year-4-month old female, it was found that the upper right canine and premolars were missing. The anamnesis revealed that their buds had been surgically removed after a trauma when she was 6 years old. The lower incisors were slightly crowded. Since the age of the patient would not permit a fixed prosthetic restoration in the next few years, it was decided to attempt an autogeneic transplant of the lower first premolars to replace the upper right canine and premolars too.

[Periodontal development after tooth germ transplantation within the framework of orthodontic treatment]

The normal development of the periodontal structures was confirmed histologically on young beagle dogs following tooth germ transplants. In humans, clinical and radiographic examinations revealed no pathology of the periodontium following transplantation of tooth germs. The grafted teeth could be moved orthodontically in the same way as any other teeth. No precautions need to be taken. This paper describes the most common indications for transplanting the tooth germs of canines, bicuspids and molars.

Retrovirus-induced insertional mutation in Mov13 mice affects collagen I expression in a tissue-specific manner

In the Mov13 mouse mutant, transcription of the alpha 1 (1) collagen gene is blocked by a retroviral insert in the first intron. We now report that teeth derived from homozygous embryos produce a dentin layer containing normal amounts of collagen 1. In situ hybridization and RNAase protection experiments indicate that the mutant allele is efficiently transcribed in odontoblasts, in contrast to other cell types. Correct splicing of the primary transcript containing the viral sequence results in a functional alpha 1 (1) collagen mRNA. The absence of a mutagenic effect in odontoblasts, as opposed to fibroblasts, suggests that the retroviral insert interferes with tissue-specific transcriptional control of the alpha 1 (1) collagen gene, most likely by inactivating cell-type-specific cis-acting regulatory elements.

[Combined surgical orthodontic therapy in a patient with multiple agenesis]

After a wide analysis of the problems concerning biology and integration of autogenic transplantation of tooth germs, the Authors present a clinical case of monolateral agenesis of two premolars, with the transfer of the second premolar germ from one side to an other, suggesting some technical details in flap scalloping.

[Autotransplantation: technic and long-term results]

Dental transplantation can be a useful and efficious technic. It was first described by Ambroise Pare and the authors have had over 12 years success and failures enough to present clinical cases and illustrations of the surgery and the orthodontic treatment. Success depends essentially on the right indication, the time and the exact methodical technic, reproducible in a treatment plan.

Morphological evidence of the formation of intracellular collagen fibrils in the embryonic mouse molar odontoblasts induced by colchicine administration

The effects of colchicine on collagen formation were examined ultrastructurally using secretory odontoblasts in mouse molar tooth germs isografted to the spleen for 1 week. Colchicine in concentrations of 0.025 or 0.05 mg/0.1 ml was injected intravenously 12-24 h prior to harvesting. Colchicine induced the disruption of the Golgi apparatus and caused the accumulation of various types of Golgi-associated vacuoles containing collagenous fibrillar structures. Many vacuoles containing fine particles, nonstriated parallel filaments, banding patterns with a periodicity of approximately 63-nm intervals, and occasionally segment-long-spacing-like assemblies were aggregated in the cytoplasm during the experimental period. These morphological changes in vacuole contents may reflect the initial steps for polymerization of the intracellular collagen fibrils. The majority of the aggregated vacuoles were degraded by fusion with lysosomes but banded filamentous material in some vacuoles appeared to polymerize into the collagen fibrils with native structures. These results suggested that in unsecreted vacuoles accumulated in the odontoblasts as a result of colchicine administration the polymerization of collagen fibrils with native structures can occur.

Ultrastructure of a new generation of odontoblasts in grafted coronal tissues of mouse molar tooth germs

Third molar tooth germs were removed from 14-day-old mice and freed from the enamel organ and follicle. After section of the apical tissues, including Hertwig's sheath, they were transplanted in 1-day-old newborn mice of the same lineage. Electron microscopy of grafts removed 7, 14 and 21 days later showed that, following the disappearance of the initial layer of odontoblasts and a period of adaptation, 14 days after transplantation newly differentiated odontoblasts deposited tubular dentine. The dentine matrix production was increased over that of controls, demonstrating that synthesis was accelerated, possibly because of lack of nerves in the grafts. Numerous characteristic structures that might be involved in the transit of proteoglycans from the Golgi apparatus were seen, as far as the extremity of the odontoblast processes. The particular experimental conditions allowed the observation in the neck region of the odontoblast of a concentration of coated vesicles which might be involved in cellular lengthening. Thus, in the presence of a fine and regular vascular network, a new generation of odontoblasts may differentiate, even in the absence of epithelial and nervous elements, and so predentine may contain inductive factors that allow the odontoblastic differentiation of pulp cells in contact with it.

Autogenic tooth transplantation: a report of ten cases

Modifications in the surgical procedure for transplantation of the unerupted mandibular third molar to the first molar socket are presented, and the clinical and radiographic data on ten cases with a 3-year follow-up are described. The proposed method of treatment makes it possible to stabilize the transplant without a splint by using a suture crossed over the occlusal surface of the tooth.