A study on mechanisms of odontoblast differentiation during reparative dentinogenesis.

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In order to elucidate mechanisms by which pulp cells differentiate into odontoblasts during reparative dentinogenesis, immunohistochemical analyses for several factors related to cell differentiation were performed. The results were as follows :1. During tooth development, differential expression of laminin-5 and integrin α6 and β4 subunits in the inner dental epithelium may be involved in ameloblast differentiation. These changes in basement membrane composition might be also related to odontoblast differentiation.2. In pulps affected by early caries, MHC class II antigen-expressing cells (HLA-DR-positive dendritic cells) aggregated mainly in the cell-free zone associated with PGP 9.5-immuno-reactive nerve fibers. In advanced caries, the accumulated HLA-DR-positive cells and PGP 9.5-immunoreactive nerve fibers showed close association with each other especially beneath the odontoblast layer. Class II molecules were recognized not only in dendritic cells but also in the Schwann cells o … More f non-myelinated nerves in the pulp. These suggested a synergistic action between immune and nervous systems in pulpal inflammation and reparative process.3. Pulpal responses after cavity preparation with either Er : YAG laser or a conventional drill were evaluated. The immunoreactivity for tissue non-specific alkaline phosphatase was more pronounced in the laser group. Clear similarities in the distribution patterns of OX6-immunopositive cells and PGP 9.5- immunoreactive nerve fibers were noted. OX6-positive MHC class II antigen-expressing cells accumulated along the pulp-dentin border and numerous bead-like PGP 9.5-immunoreactive nerve fibers were observed under the odontoblastic layer, suggesting their involvement in pulp tissue repair and reparative dentin formation.4. During hard tissue formation in the pulp cavity of rat molar after transplantation into subcutaneous tissue, non-collagenous proteins, such as osteocalcin, osteopontin, bone sialoprotein and dentin sialoprotein showed different distribution patterns in newly-formed hard tissues in the coronal, root canal and apex areas, respectively. These suggested that each hard tissue was formed by differently-derived cells. Less