A study on mechanisms of tissue formation and regeneration of the dentin-pulp complex

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This study aims to elucidate mechanisms of tissue formation and regeneration of the dentin-pulp complex. The results were as follows :1. During mouse tooth development, the expression of an intermediate filament nestin was intense in differentiating odontoblasts, and became restricted to the secretory pole of functional odontoblasts, suggesting that nestin plays a role in terminal differentiation, especially in cell elongation and/or polarization of odontoblasts.2. Distinct temporal and spatial expression patterns of TIMPs suggest divergent functions of these factors in incisor organogenesis. Intense expression of Timp-1 was detected in differentiating odontoblasts, while Timp-3 was expressed by subodontoblasts, suggesting their involvement in odontoblast differentiation.3. The unerupted rat incisor was composed of osteodentin, with numerous cells present in the anterior apex. The osteodentin was immunopositive for osteocalcin, bone sialoprotein, and dentin sialoprotein, with an immunolocalization pattern similar to that of dentin. These results indicate that osteodentin in the rat incisor possesses a dentin-like characteristics.4. We performed a histological and immunohistochemical evaluation of mineralized tissue induced by pulp transplantation into subcutaneous tissue. The results indicate that pulp cells are able to form hard tissue with bone- or cementum-like characteristics without dentin influence. Calcification may start in necrotic cells and matrix vesicles, followed by collagenous calcification.5. Pulpal responses to GaAlAs laser irradiation were elucidated. The results indicated that the GaAlAs laser may induce the formation of tertiary dentin by influencing the secretory activity of odontoblasts. However, higher energies may cause irreversible changes to the pulp, often leading to the formation of an intrapulpal bone-like tissue.