Abstract: Objective To compare the changes in the angulation and eruption space of the mandibular third molars in adult patients with ClassⅡmalocclusion orthodontically treated with different extraction patterns, and to discuss the effects of different therapies on the eruption of mandibular third molars. Methods 90 adult patients with ClassⅡmalocclusion were chosen, which were divided into three groups: non-extraction group (n=30); the first premolar extraction group (n=30); the second premolar retraction group (n=30). The panoramic radiographs were taken before and after treatment. The differences of the angulation and eruption space of the mandibular third molars were compared before and after treatment to predict its’ eruption. Result Compared with non-extraction group, the angulation and eruption space of mandibular third molars improved and increased significantly after treatment with the first and second premolar extraction groups (P＜0.05). There were significant differences in the eruption space change among three groups (P＜0.001). The difference of the eruption space between the non-extraction group was greater than that in the first premolar extraction group, and the first premolar extraction group was greater than that in the second premolar extraction group. The prediction of eruption of the mandibular third molar was the best in the second premolar extraction group, followed by the first premolar extraction group and then non-extraction group. Conclusion Mandibular first or second premolar extraction increases the angulation and eruption space of mandibular third molars. And the closer the third molar is to the extraction site, the more angulation and eruption space improve, the more likely it is to become erupted.

Key words: [Key words]Class Ⅱ malocclusion, mandibular third molar, angulation, eruption space