骨性Ⅱ类错[牙合]拔牙矫治前后下颌牙弓与基骨形态的变化

Morphological changes of dental and basal arch forms in skeletal class Ⅱ malocclusions before and after extraction treatment

目的通过三维数字化模型，利用WALA嵴分析骨性Ⅱ类错[牙合]畸形患者拔牙矫治前后下颌牙弓和基骨形态的变化，以期为临床治疗提供相关指导。方法扫描25例骨性Ⅱ类错[牙合]畸形患者治疗前后的下颌模型，标定各牙FA点及对应WALA点，利用WALA点通过最小二乘法确定参考平面，并得到临床冠中心（FA点）和膜龈联合处软组织最凸点（WALA点）在参考平面的投影。建立相应坐标系并拟合生成基骨弓及牙弓所对应的曲线，分析治疗前后牙弓和基骨形态的变化和关系。结果治疗后基骨前、中、后段分别增加（0.835±1.259） mm，（1.700±1.280） mm，（2.170±1.227） mm。治疗后牙弓前段宽度缩窄（3.345±2.907） mm，后段宽度增加（1.110±1.566） mm，中段无明显变化。结论骨性Ⅱ类错[牙合]畸形患者拔牙治疗后下颌基骨中后段宽度增加，整体形态基本稳定，而牙弓前段宽度减小，后段宽度增大。治疗后牙弓与基骨形态更加匹配，有利于功能和稳定。

ObjectiveTo study the variation of the dental and basal arch forms before and after orthodontic treatment of patients with skeletal class Ⅱ malocclusion by tooth extraction. MethodsThe mandibular dental casts of 25 skeletal class Ⅱ patients were laser scanned before and after treatment. The facial axis （FA） points, which were used to represent the dental arch, and the WALA point, which were used to represent the basal bone, were identified for each tooth from the right first molar to the left first molar. We constructed the curve with points of projection of the FA and WALA point on the reference plane, and compared the curve of dental arch and basal bone before and after treatment. ResultsThe width of anterior middle and posterior of the basal arch increased （0.835±1.259） mm, （1.700±1.280） mm and （2.170±1.227） mm, respectively. While the dental arch had a wider width （1.110±1.566） mm in posterior segment but a narrower one in anterior （3.345±2.907） mm. ConclusionsThe width of middle and posterior of basal bone represented by WALA ridge becomes wider after orthodontic treatment with tooth extraction in patients with skeletal class Ⅱ malocclusion, while the dental arch turns to a new form, which is more coordinated to the basal bone.