[Hertwig's epithelial root sheath, bone matrix proteins, and initiation of cementogenesis in mouse teeth]

The aim of this study was to analyze the association between Hertwig's epithelial root sheath (HERS), noncollagenous matrix proteins, and cementogenesis.Eighteen BALB/c postnatal mice were divided into five groups according to the developing stages. The mouse teeth were examined at the onset of root development by light and transmission electron microscopy. PV two-step immunohistochemical method was used to detect the expression of proliferating cell nuclear antigen(PCNA), OPN and BSP during the root formation.Hertwig's epithelial root sheath, which derived from the apical extensions of inner and outer enamel epithelium, was formed at 5-day mouse teeth and expressed PCNA positively. During the fuse of inner and outer enamel epithelium, some cells, which displayed the cytologic features of protein synthesis and secretion, could be found between the two epithelium cells. Desmosomal cell junctions were observed. The positive expressions of OPN were observed at the beginning of HERS. An accumulation of OPN could also be observed at the dentin-cementum junction during cementogenesis, but no positive BSP signals were seen at the onset of HERS.At onset of HERS, the inner enamel epithelium, outer enamel epithelium embrace several cells with developed cytoplasmic organelles, which may derive from stratum intermedium or stellate reticulum, and form a structure like enamel organ, which may be associated with initial cementogenesis. OPN, the non collagenous matrix proteins of cementum, may also take part in the formation of the dentin-cementum junction.