中文摘要：

目的：分析总结与下颌埋伏第三磨牙断根有关的影像学或临床表现,分析断根风险的相关因素以指导临床。方法：2013-11—2014-10期间共收集91例下颌埋伏阻生的第三磨牙患者的完整术前、术中相关影像学和临床表现数据并分析。所有患者在同样环境标准流程下治疗,由未提前告知研究目的不同临床医生处理。结果采用卡方检验或t检验。结果 ：91例病例中,12例在拔牙术中出现断根（断根率13.1%）。经统计分析,患者年龄、阻生深度、牙根数目、医生资历均与断根发生率有相关（P〈0.05）。在多根牙,拔牙方式（是否分根）对断根发生有意义。经统计分析,其他因素与断根发生之间无相关。结论：与下颌阻生第三磨牙拔除时断根相关的高危因素有患者年龄、阻生深度、医生经验、牙根数目和拔除方式。

英文摘要：

Objective： The aim of this prospective study was to investigate radiologic and clinical factors associated with root fracture during the removal of impacted mandibular third molars. Methods： A total of 91 patients who required 91 surgical extractions of impacted mandibular third molars from November 2013 to October 2014 were involved in the study.Radiologic and clinical data were taken preoperatively as well as intraoperatively. All surgical procedures were performed under the same conditions and by the different surgeons who were unaware of the data collected in the pre-selection phase.Either Pearson＇s chi-square test or Fisher＇s exact test was used for the data analysis. Results： Among these 91 patients with impacted mandibular third molars, root fractures were seen in 12 patients（13.1%） during the surgical interventions.There were a highly significant increase in the incidence associated with increasing patient＇s age（ P〈0.05）, depth of impaction（P〈0.05）, number of roots（P〈0.05） and surgeon＇s experience（P〈0.05）. For the multi-rooted tooth, the incidence of root fracture was associated with extraction method（root not split）（P〈0.05）. Statistical analyses revealed that the root fracture was unrelated to the other variables. Conclusion： Major risk factors closely associated with the increase incidence of surgical difficulties and intraoperative root fracture, during the surgical removal of impacted mandibular third molars, are patient＇s age, depth of impaction, surgeon＇s experience, number of roots and extraction methods.