AIM To describe four cases of an uncommon type of segmental root development after endodontic revitalization procedures. The formation, development and prognosis of this phenomenon are discussed, along with the causes and preventive measures. SUMMARY This report describes one immature maxillary anterior tooth with an extensive periapical lesion after partial extrusion caused by trauma and three immature mandibular premolars with extensive periapical lesions after fracture of the dens evaginatus. All four teeth underwent revitalization procedures. During follow-up, an uncommon type of segmental root development was observed in each case, where the apical segment appeared to detach from the body of the root and developed separately. In all cases, the detached apical root segments continued to develop with a shape and structure similar to that of a normal root tip. However, further development of the root body did not appear to occur. The follow-up times of the present cases were 11, 60, 41 and 67 months, respectively. All four teeth remain intact and functioned normally without symptoms. Cases 2 and 3 displayed positive reactions to electrical pulp tests during follow-up. KEY LEARNING POINTS Trauma and extensive periapical inflammation may result in the detachment of Hertwig's epithelial root sheath (HERS) and apical papilla from the root, thus creating a separate apical root segment. Formation of an apical root segment could be regarded as evidence of displacement of the HERS and apical papilla. Once this occurs, there is no chance that the main root of the tooth will develop into a normal-sized root. This type of segmental root development is always possible. If the teeth have suffered from severe trauma or have long-term and large periapical lesions before revitalization, the possibility of segmental root development should be considered. During the process of revitalization, intracanal bleeding is induced by rotating a pre-curved K-file 2 mm past the apical foramen. This procedure should be done gently to protect the apical structures and avoid iatrogenic factors that could lead to abnormal root development.

中文翻译：

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活化后不常见的节段根发育类型。

目的 描述 4 例不常见的牙髓再生手术后节段性牙根发育的案例。讨论了这种现象的形成、发展和预后，以及原因和预防措施。总结 本报告描述了一颗未成熟的上颌前牙在外伤引起的部分挤压后具有广泛的根尖周病变，以及三颗未成熟的下颌前磨牙在外伤引起的外伤后具有广泛的根尖周病变。所有四颗牙齿都接受了修复程序。在随访期间，在每种情况下都观察到一种不常见的节段性根发育，其中顶端部分似乎与根体分离并单独发育。在所有情况下，分离的根尖部分继续发育，其形状和结构与正常根尖相似。然而，似乎没有发生根体的进一步发展。本次病例随访时间分别为11、60、41、67个月。所有四颗牙齿都完好无损，功能正常，没有任何症状。病例 2 和 3 在随访期间对电浆测试显示阳性反应。关键学习点 创伤和广泛的根尖周炎症可能导致 Hertwig 上皮根鞘 (HERS) 和根尖乳头从根部脱离，从而形成一个单独的根尖节段。根尖根段的形成可被视为 HERS 和根尖乳头移位的证据。一旦出现这种情况，牙齿的主根不可能发育成正常大小的牙根。这种类型的节段根发育总是可能的。如果牙齿在修复前曾遭受过严重外伤或有长期较大的根尖周病变，则应考虑节段性牙根发育的可能。在再生过程中，通过将预先弯曲的 K 锉旋转超过根尖孔 2 毫米来诱导根管内出血。此过程应轻柔地进行，以保护根尖结构并避免可能导致根部发育异常的医源性因素。应考虑节段根发育的可能性。在再生过程中，通过将预先弯曲的 K 锉旋转超过根尖孔 2 毫米来诱导根管内出血。此过程应轻柔地进行，以保护根尖结构并避免可能导致根部发育异常的医源性因素。应考虑节段根发育的可能性。在再生过程中，通过将预先弯曲的 K 锉旋转超过根尖孔 2 毫米来诱导根管内出血。此过程应轻柔地进行，以保护根尖结构并避免可能导致根部发育异常的医源性因素。