Abstract:

Objective To analyze the effects about inclinations of the second and the third molars in patients treated with or without premolar extractions. Methods Fifty- six adolescents were chosen and divided into the first premolar extraction and non- extraction groups, 30 and 26 patients respectively. The pre- treatment and post- treatment panoramic radiographs were made. Angles between long axis of the third molar and the occlusal plane（the second molar alike）, and long axis of the second and the third molar were measured and evaluated. Results The maxillary and mandibular third molar angulations were all improved after treatment in two groups. Compared with non - extraction group, the average changes of angle between long axis of the third molar and the occlusal plane increased significantly in maxilla and mandible（P<0.05）. Average changes of angles between long axis of the second and the third molar decreased and had statistically significant difference（P<0.05）. The change of angle between long axis of mandibular second molar and the occlusal plane had statistically significant difference（P<0.05）, but there was no statistically significant difference in maxillary second molar（P >0.05）. Conclusion The first premolar extraction in orthodontic treatment could improve the third molar angulations and it would promote the eruption of the third molar.

Key words: the first premolar extraction, non- extraction treatment, the third molar angulation