下颌第三磨牙近中阻生相关因素的头影测量分析

目的探讨成人下颌第三磨牙(M3)近中向阻生或萌出的机制及其与颌骨发育的关系。方法选取72例正畸患者为研究对象,术前拍摄全景X线片和头颅定位侧位片。通过全景X线片观察下颌M3阻生或萌出的情况,将其分为阻生组和萌出组,并对其X线头颅侧位片进行头影测量分析。结果阻生组与萌出组的下颌体长度(Go-Po’)、下颌支宽度(W)、下颌平面角(MP-FH)、前下面高(ANS-Me)、下颌支长度与下颌骨长度的比值(Co-Go/Co-Po)的差异有统计学意义(P<0.05),阻生组的W、Co-Go/Co-Po大于萌出组,而Go-Po’、ANS-Me、MP-FH小于萌出组。两组间的Co-Po、Co-Go、上下中切牙角、上牙槽座点-鼻根点-下牙槽座点角的差异无统计学意义(P>0.05)。结论下颌M3的近中向阻生和萌出可能与下颌的旋转生长及面部生长型有关,下颌向前旋转和短面型患者的下颌M3更易发生近中向阻生。

A cephalometric study on relevant factors of the mesial impaction of mandibular third molars

Objective To evaluate the mechanism of the mesial impaction of mandibular third molars(M3) in adults and the relationship between the mesial impaction or eruption of M3 and the development of maxillary and mandible.Methods 72 subjects who have taken panoramic radiographs and lateral cephalometric radiographs before orthodontic treatments were divided into two groups based on the status of M3: Impaction group and eruption group,and all cephalometric radiographs were analyzed for the two groups.Results Mandibular body length(GoPo’),ramal width(W),mandibular plane angel(MP-FH),lower anterior face height(ANS-Me) and ramal length/mandibular length ratio(Co-Go/Co-Po) were significantly difference(P<0.05) in the impaction group than in the eruption group.W and Co-Go/Co-Po were significantly increased(P>0.05) and Go-Po’,ANS-Me,MP-FH were decreased in the impaction group.The impaction and eruption groups did not differ significantly(P<0.05) in respect to Co-Po,Co-Go,U1-L1 angel and ANB angle.Conclusion The mesial impaction or eruption of mandibular M3seemed to be relevant to the rotational growth of the mandibles and the pattern of facial growth. M3 mesial impactions were more likely to occur in subjects with anterior facial rotation and short facial forms.