关键词: 正畸治疗, 拔牙矫治, 非拔牙矫治, 第三磨牙倾斜度

Abstract:

Objective  To compare the inclinations of third molars of patients treated orthodontically with and without premolar extractions. Methods  Records of 37 first premolar extraction patients and 32 nonextraction patients were examined. The pretreatment and posttreatment panoramic radiographs were analyzed. The angles were measured between the long axis of the third molar and the occlusal plane and between the long axis of the third molar and the long axis of the second molar. Changes in third molar angulations from pretreatment to posttreatment for two groups were compared by Mann-Whitney U-test. Results  There were statistically significant difference between the extraction and nonextraction groups in the median angle formed by the long axis of third molar angulation relative to the occlusal plane（P<0.05） and the second molar（P<0.05） in mandible but not in maxillary. In the extraction group, at the end of the orthodontic treatment, the mandibular third molars showed more uprighting than did the maxillary third molars. Conclusion  Orthodontic treatment involving premolar extractions improves mandibular third molar angulations.

Key words: orthodontic treatment, extraction, nonextraction, third molar angulation