Position change of mandibular third molar after extraction or non-extraction orthodontic treatment in patients with Class II~1 malocclusion

Objective To study the impact with extraction or non-extraction orthodontic treatment on mandibular third molar. Methods Twenty-seven patients of Class Ⅱ1 malocclusion in 2002—2005 were chosen randomly,and they were divided into two groups according to their extraction or non-extraction orthodontic treatment. Their panoramic radiographs of pretreatment and post-treatment were analysed. Results After orthodontic treatment, eruption space of mandibular third molar(BX) increased in the two groups;changes were statistically significant(P 0.05). Mesioclination angle of mandibular third molar decreased in the extraction group, but increased in the non-extraction group;difference between the two groups was also statistically significant(P 0.01). Though changes of mandibular third molar eruption space with mandibular third molar crown width ratio(BX/MD)were significant in the extraction group,but changes of the ratio of the two groups had no statistical significance when compared. Conclusion For Class Ⅱ1 patients who are in the growing period,extraction orthodontic treatment is more conducive to mandibular third molar’s eruption.