研究结果表明，在相同致伤条件下，伴有下颌骨骨折的颌面部火器伤的颅脑伤发生率高于无下颌骨骨折的颌面伤。
It was found that under the same wounding condition, the rate of cerebral damages was higher when the mandible was fracture than when the mandible was intact.
结论：咬颌创伤，牙周疾病，牙髓无活力等是导致牙根纵裂的重要原因。
CONCLUSION: Traumatic occlusal force, periodontal lesions, teeth with root canal therapy are the major causes that led to vertical root fractures.
盔甲鱼 类是古生代中期化石 无 颌 类的主要 类群，其分布主要限于我国境内以及越南北部。
The Galeaspid is one major group of Agnatha in the Middle Paleozoic, and is mainly distributed in China and North Vietnam.
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