下颌第三磨牙的萌出可分为萌出前期：下颌第三磨牙在下颌升支底部发育，咬合面向近中倾斜；萌出期：牙胚沿牙体长轴移动，伴近中移动；萌出后期：下颌第三磨牙萌出到咬合功能位置后，终身伴有轴向和近中向的移动。影响下颌第三磨牙萌出间隙的因素包括下颌升支前缘的改建性骨吸收，下颌牙弓和牙槽向前的生长量，下颌体矢状向的生长量；影响下颌第三磨牙萌出角度的因素包括下颌第三磨牙的萌出间隙、牙根发育状况和患者的矢状骨型等。评价第三磨牙萌出间隙和萌出角度的手段有X线头颅侧位片、全颌曲面断层片和锥形束CT。拔除前磨牙对第三磨牙萌出的影响尚无定论。下颌第三磨牙的萌出受多因素影响，目前尚不能进行准确的预测。%The mandibular third molar eruption is commonly divided into three phases: pre-eruptive phase, the process of developing at the bottom of mandibular ramus as well as moving forward; pre-functional eruptive phase, dental germ moving along the axis of tooth with mesial movement; functional eruptive phase, gingival emergence to the occlusal plane. The factors affecting eruption space were modeling resorption of the mandibular ramus, growth amount of the mandibular arch and alveolar bone, sagittal growth amount of mandibular body, etc.. And eruption angulation was another variable associated with retromolar space, the development of root, sagittal skeletal classification, etc.. As for the methods to evaluate eruption space and angulation of third molar, cephalometric radiograph, panoramic radiograph and cone beam CT were included. However, it is not clear whether premolar extraction orthodontic treatment can have effects on the mandibular third molar eruption. Other factors may influence the angulation and position of the mandibular third molar and that it is not possible to predict exactly.
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