Objective To analyze the anterior mandibular profile feature of the patients with lower anterior crowding. Methods The hard and soft tissue profile of anterior mandible on the lateral cephalogram were detected by digital image processing software MATLAB 7.5.0 with Canny edge detection algorithm. Then the profile differences between the patients with lower anterior crowding and the normal individuals were compared. Results For the hard tissue profile of the anterior mandible.the position of B point was significantly lower and retraller (P<0.05) in the female patients than in the female normal individuals, and the mentolabial sulcus was deeper (P<0.05).ln the male patients.the position of B point were significantly retraller (P<0.05) and the mentolabial sulcus was deeper (P<0.05) than in the normal individuals. For the anterior mandibular soft tissue profile, comparison of the depth of edges profile curve between subjects and control groups for female soft-tissue showed no significant difference (P>0.05).ln contrast, the depth of edges profile curve was significant increased in case groups for men, with deeper mentolabial sulcus (P<0.05). Conclusion For the patients with lower anterior crowding, it is the features that the anterior mandible alveolar base is hypoplastic.For the female patients.the mentolabial sulcus is not significantly deeper because of the soft tissue compensation.But for the male patient.the deeper mentolabial sulcus is resulted because of the hypoplastic alveolar base.%目的:分析下前牙拥挤患者的下颌前部侧貌轮廓特征.方法:应用MATLAB7.5.0数字图像处理软件,采用Canny边缘检测算法实现数字X线头颅侧位定位片上下颌前部软、硬组织边缘线的自动提取.比较下前牙拥挤患者与正常(牙合)个体下颌前部软、硬组织边缘线的差异性.结果:从下颌前部硬组织边缘曲线来看,女性下前牙拥挤患者相对于正常(牙合)个体,下齿槽座点B的位置明显下移(P＜0.05),矢状向位置也偏后(P＜0.05),颏唇沟深度明显变深(P＜0.05).男性下前牙拥挤的患者相对于正常(牙合)个体,下齿槽座点B的矢状向位置显著后缩(P＜0.05),颏唇沟深度明显变深(P＜0.05).从下颌前部软组织边缘曲线来看,女性下前牙拥挤患者相对于正常(牙合)个体颏部软组织侧貌轮廓曲线无明显差异性(P＞0.05)；而男性下前牙拥挤患者颏部软组织侧貌轮廓线曲度增加,颏唇沟变深(P＜0.05).结论:下前牙拥挤的患者有下颌前部齿槽基骨有发育不足的特点.女性下前牙拥挤患者的颏部软组织会产生一定的代偿,使下颌侧貌软组织不显现颏唇沟加深的情况；而男性下前牙拥挤的患者,则会显现较为明显的因下颌前部齿槽基骨发育不足造成的颏唇沟加深情况.
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