Abstract: Objective    To analyze the impact of maxillary third molar impaction on the position of maxillary molars in adult patients with skeletal class Ⅱ high-angle malocclusion. Methods    A retrospective analysis was conducted on the clinical and imaging data of 40 adult patients with skeletal class Ⅱ high-angle malocclusion who were treated in the Department of Orthodontics at Dalian Stomatological Hospital from 2018 to 2020. Among them，there were 20 patients with normal eruption of maxillary third molars on both sides（the eruption group），and 20 patients whose maxillary third molar crowns were fully formed but had not erupted on both sides（the impacted group）. Cone beam CT（CBCT）was used to measure and analyze the angle of the maxillary first molar（A-U6），the angle of the maxillary second molar（A-U7），the inclination of the maxillary occlusal plane（FHP-MOP），the height of the maxillary first molar（FHP-U6，PP-U6），the height of the maxillary second molar（FHP-U7，PP-U7），subfacial height（ANS-ME），total length of the palatal plane（ANS-PNS），anterior palatal plane length（ANS-U6），and the ratio of ANS-U6 to ANS-PNS（A6/AP）. Results    The comparison of the measurement results for the angle of maxillary molars（A-U6，A-U7）and the height of maxillary molars（PP-U6，PP-U7，FHP-U6，FHP-U7）between the eruption group and the impacted group showed no statistically significant differences（all P > 0.05）. Therefore，the average values of the left and right sides of the two groups were used for inter-group comparison. A-U6，A-U7，FHP-U6 and FHP-U7 in the eruption group were all greater than those in the impacted group，while FHP-MOP，ANS-ME，ANS-U6 and A6/AP were all lower than those in the impacted group，with differences being statistically significant（all P < 0.05）. There was no significant difference in PP-U6，PP-U7 or ANS-PNS between the two groups（all P > 0.05）. The A6/AP of impacted group was 0.53 ± 0.06. Conclusion    In adults with skeletal class Ⅱ high angle malocclusion，compared to the eruption of the maxillary third molar，the crowns of the maxillary first and second molars in the impacted state of the maxillary third molar are tilted more distally，the height of the maxillary molars is reduced，and the inclination of the maxillary occlusal plane is greater. Maxillary posterior dentoalveolar discrepancy may lead to the impaction of the maxillary third molar.

Key words: maxillary third molar, impaction, skeletal class Ⅱ, high angle malocclusion, cone beam CT

摘要： 目的    分析上颌第三磨牙阻生对骨性Ⅱ类高角错畸形成人患者上颌磨牙位置的影响。方法    选取2018—2020年于大连市口腔医院正畸科就诊的40例骨性Ⅱ类高角错畸形成人患者的临床和影像学资料进行回顾性分析，其中两侧上颌第三磨牙均正常萌出患者20例（萌出组），两侧上颌第三磨牙牙冠均已形成但未萌出患者20例（阻生组）。应用锥形束CT影像测量分析2组患者上颌第一磨牙角度（A-U6）、上颌第二磨牙角度（A-U7）、上颌平面倾斜度（FHP-MOP）、上颌第一磨牙高度（FHP-U6、PP-U6）、上颌第二磨牙高度（FHP-U7、PP-U7）、面下高（ANS-ME）、腭平面总长度（ANS-PNS）、前腭平面长度（ANS-U6）及ANS-U6与ANS-PNS的比值（A6/AP）。结果    萌出组、阻生组左右两侧上颌磨牙角度（A-U6、A-U7）、上颌磨牙高度（PP-U6、PP-U7、FHP-U6、FHP-U7）测量结果比较，差异均无统计学意义（均P > 0.05），因此将2组左右两侧数据取均值进行组间比较。萌出组的A-U6、A-U7、FHP-U6及FHP-U7均大于阻生组，FHP-MOP、ANS-ME、ANS-U6及A6/AP均小于阻生组，差异均有统计学意义（均P < 0.05）。2组PP-U6、PP-U7、ANS-PNS比较，差异均无统计学意义（均P > 0.05）。阻生组A6/AP为0.53 ± 0.06。结论   在骨性Ⅱ类高角错畸形成人患者中，与上颌第三磨牙萌出时比较，上颌第三磨牙阻生状态下的上颌第一、第二磨牙牙冠更向远中倾斜，上颌磨牙高度降低，上颌平面倾斜度较大；上颌磨牙后部空间不调可能导致上颌第三磨牙阻生。

关键词: 上颌第三磨牙, 阻生, 骨性Ⅱ类, 高角型, 锥形束CT