小鼠磨牙上皮根鞘与牙骨质发育的关系

目的：研究上皮根鞘细胞（Hertwig’s epithelial root sheath，HERS）的发生，非胶原基质蛋白骨桥素（osteopontin，OPN）、骨涎蛋白bone sialoprotein，BSP）及牙骨质发育之间的关系。方法：取出生后5d、9d、15d、19d及4个月的BALB／c小鼠共18只，光镜观察上皮根鞘的发生、牙骨质发育过程，透射电镜观察该阶段上皮根鞘细胞的超微结构。PV免疫组化两步法检测增殖细胞核抗原（proliferating cell nuclear antigen。PCNA）、OPN、BSP在牙骨质形成过程中的表达。结果：超微结构观察发现，内、外釉上皮在融合过程中，2层细胞间包含个别具有丰富细胞器的一类细胞。其胞质中可见大量的高尔基复合体和粗面内质网，通过桥粒与内、外釉上皮连接。免疫组化显示，新形成上皮根鞘细胞呈OPN阳性表达，但未见BSP阳性表达。在牙根的发育过程中，牙本质一牙骨质交界处OPN有较高表达，伴随牙骨质基质在根面不断沉积，OPN在牙骨质中表达增强，成熟牙根表面可见厚度不同的牙骨质覆盖，OPN阳性表达。结论：上皮根鞘发生时，内、外釉上皮间可包容个别源于网状层或中间层、细胞器丰富的细胞，从而形成类似成釉器的结构。其可能在牙根发育起始阶段分泌某些蛋白和信号分子，启动根部牙本质和牙骨质的形成。

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

PURPOSE:The aim of this study was to analyze the association between Hertwig's epithelial root sheath(HERS),noncollagenous matrix proteins,and cementogenesis.METHODS: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.RESULTS:Hertwig's epithelial root sheath,which derived from the apical extentions 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.CONCLUSION: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.