上皮根鞘细胞在牙骨质发育中的作用

目的：观察牙根发育中上皮根鞘细胞（Hertwig＇s epithelial root sheath,HERS）断裂后结局和增殖凋亡相关基因的表达,探讨上皮根鞘在牙根发育特别是牙骨质形成中的可能作用.方法：用TUNEL（ TdT- mediated - dUTP nick end labeling , TUNEL） 法原位细胞凋亡检测牙根发育中上皮根鞘细胞凋亡的情况.以细胞角蛋白14（cytokeratin 14）标记上皮根鞘细胞,追踪其断裂后结局.SP免疫组化法检测增殖细胞核抗原（proliferating cell nuclear antigen, PCNA ）和凋亡抑制基因Bcl-2在上皮根鞘细胞的表达.结果：牙冠形成后,内外釉上皮结合增殖形成HERS,此时呈PCNA表达阳性;牙根发育开始后,HERS呈Bcl-2阴性表达,在少量牙本质基质形成处,上皮根鞘细胞开始呈TUNEL阳性表达,之后HERS断裂,在其外侧可见成牙骨质细胞的形成,断裂的HERS细胞部分转入牙周膜形成上皮剩余（the epithelial rest of Malassez）,而细胞牙骨质形成中可见部分埋入细胞呈CK14阳性表达.结论： HERS细胞的凋亡可能会为成牙骨质细胞分化提供信号,部分HERS细胞可能参与牙骨质的形成.

Role of Hertwig''''s epithelial root sheath in the developing cementum

AIM:To analyze the apoptosis and proliferation of HERS (Hertwig's epithelial root sheath) and to evaluate the roles of HERS cells in the development of cementum. METHODS: Apoptosis was identified by the terminal deoxy-transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) method. Cytokeratin 14(CK 14) was applied as a special marker of HERS cells. SP immunohistochemical method was used to detect the expression of Bcl-2 protein and PCNA (proliferating cell nuclear antigen). RESULTS:After the completion of crown formation, the inner and outer enamel epithelia fused below the level of crown cervical enamel to produce a bilayered epithelial sheath termed HERS, which positively expressed PCNA but negatively Bcl-2. Immediately after formation of predentin, HERS postively expressed TUNEL and then disintegrated. Cementoblasts could be found beside these disintegrated HERS. Latterly some cells migrated into the periodontal ligament and aggregated to form ERM cell clusters. However, several cells incorporated in the cementum, positively expressed CK14, which hinted their epithelial origin. CONCLUSION:Apoptosis of HERS cells may be the signal of cementum development, and some HERS cells may be directly participate in the progress.