关键词: 全景X线片, 第三磨牙, 阻生, 头影测量分析

Abstract:

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（Go- Po’）, 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 M3 seemed 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.

Key words: orthopantomograph, third molar, impaction, cephalometric analysis