The role of host tissue in repair of transplanted mouse molar teeth: a reappraisal of induction of odontoblasts during tooth development and repair

Immunolocalization of fibronectin during the early response of dog dental pulp to demineralized dentine or calcium hydroxide-containing cement

The role of fibronectin during the events initiating the post-developmental histogenesis of dentine was investigated by exposing the pulp to implants of autogenous demineralized dentine or calcium hydroxide-containing cement for short periods. Implants exposed for 3 days were processed for immunoelectron-microscopic analysis of fibronectin adsorption on to their surfaces. The localization of fibronectin in the critical area of interaction was examined by immunofluorescence 6, 14 and 21 days after implantation. Heavy adsorption of fibronectin on to the dentine implants and the crystalline structures that had been deposited on the cement implants was demonstrated. Positive fluorescence was consistently seen around dentine implants. Strongly immunopositive fibroblast-like cells and weakly reactive, differentiating odontoblast-like cells were found in association with the implanted matrix. Uncalcified matrix secreted by the polarized or non-polarized cells was consistently rich in fibronectin. Fibroblast-like cells exhibiting intense immunoreaction only at 14 and 21 days were mainly associated with the crystalline precipitates on the cement surfaces or within the surrounding pulp. The findings indicate that the specific inductive effects of demineralized dentine on pulp cells are initiated by exposure of the pulp to a fibronectin-containing surface; adhesion of pulp cells and synthesis of a fibronectin-rich matrix characterize the development of new dentine. The reparative response to non-specific inductive influences such as calcium hydroxide seems to be mediated by progressive enhancement of fibronectin synthesis in pulp cells.

Mechanisms controlling secondary initiation of dentinogenesis: a review

Dentinogenesis can be initiated secondarily as an intrinsic ability of the dental pulp to repair, or after interaction of pulp cells with specific exogenous inductive factors. In the present article the basic developmental aspects, highlighting the mechanism by which dentinogenesis is initiated during tooth development, are discussed. Furthermore, clinical and experimental observations concerning the events taking place during secondary initiation of dentine formation, as part of exposed or non-exposed pulp tissue repair, or as a result of dentine matrix or other chemical-pulp cell interactions, are reviewed. Discussion includes hypotheses relating to the crucial biological steps leading to expression of odontoblastic-like cell phenotype and secondary initiation of dentine histogenesis.

Short-term dentinogenic response of dog dental pulp tissue after its induction by demineralized or native dentine, or predentine

The events initiating the expression of odontoblastic potential by pulpal ectomesenchymal cells were investigated by exposing the pulp to demineralized, native and unmineralized autogenous dentine. The pulp responses to implants were histologically evaluated 3, 7 and 10 days postoperatively, while the surface structure of the newly mineralized matrices was examined 12 and 28 days after implantation. Differentiation of odontoblast-like cells in close proximity to the implanted matrix was consistently demonstrated after exposure to predentine. Scattered columnal cells undergoing polarization, characterized ultrastructurally by the orientation of their rough endoplasmic reticulum, were also found in direct contact with the demineralized dentine. However, in response to demineralized implants, groups of differentiated odontoblast-like cells were clearly seen only in association with a zone of matrix secreted in a polar, predentine-like pattern, indicating an asynchronous inductive influence of this type of implant on pulp cells. Further, the response of pulp cells to native dentine was characterized by the elaboration of a two-layered matrix (a fibrous and a polarly deposited matrix) before initiation of secondary dentinogenesis. Scanning electron microscopy of the newly deposited matrices revealed differences between the indirect matrix synthesis, observed in short-term response to implants of demineralized or native dentine, and the specific, dentinogenic function of the odontoblast-like cells. These observations indicate that the dentine-induced dentinogenesis is initiated by two mechanisms--direct induction of odontoblast-like cells as well as indirect matrix synthesis, which further controls cell polarization. Immobilization of the cells on implanted matrix seems to be the critical requirement for direct expression of the odontoblastic phenotype.

Differentiation of odontoblasts in mouse dental papillae recombined with normal or chemically-treated dentinal matrices

Separation and recombination experiments were made with manually or trypsin-dissociated dental papillae (day 15, 16, 17, 18 in utero and 2, 7, 14 postnatal) and manually isolated hard tissues of the third molar crown (14 postnatal days). Several series of hard tissues were further treated with citric acid, hyaluronidase or sodium hypochlorite. The recombinations were transplanted into the subcutaneous tissue of new-born mice. Grafts were removed 7, 14 and 21 days later and prepared for light and electron microscopy. Whatever the age of the papilla and whatever the treatment of the crowns, well-characterized odontoblasts differentiated and deposited new layers of tubular dentine, except when the recombined dental papilla was 15 days old. These findings indicate that odontoblasts are very early committed (since day 16 in utero) and that they may differentiate in dental papillae in contact with chemically altered dentinal matrices.

Differentiation of odontoblasts in grafted recombinants of murine epithelial root sheath and dental mesenchyme

The epithelial root sheath (ERS) was isolated from first molars of 5-day-old post-natal CD-1 mice using trypsin. After isolation, ERS cells remained viable in vitro and immunohistochemical examination of cultures confirmed the epithelial phenotype and the absence of mesenchymal contamination. Recombinants of isolated ERS and dental papilla resulted in odontoblast differentiation within cells of the dental papilla, and the formation of root-like fragments of dentine after 2 weeks of intra-ocular grafting. These findings indicate the inductive influence of the ERS on dental papilla cells.

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.