[摘要]目的通过全景片分析成都地区12岁青少年第三磨牙(M3)的发育情况。方法随机抽取四川大学华西口腔医院影像资料库12岁青少年的全景片449张，根据观察的结果将M3的发育状况进行分级统计，分析不同性别以及上下颌骨和两侧颌骨M3的发育情况。结果12岁青少年M3的发育情况为：大部分牙冠已钙化，牙冠呈帽状，而且男性与女性的发育情况差别不明显。大部分下颌M3较上颌M3发育得更早，左右两侧M3分别占60.69%和64.25%。上颌M3以垂直向生长为主，下颌M3以近中向生长为主。结论12岁青少年M3牙冠大部分已经钙化，下颌发育早于上颌。

    [关键词]全景片；第三磨牙；牙胚；发育；阻生

    [中图分类号]R 814[文献标志码]A[doi]10.3969/j.issn.1673-5749.2012.03.005

    Study on the development of third molar of the twelve-year-olds in Chengdu through X-ray filmsRen Jiayin, Wang Hu, Li Guo, Zhao Shuping, Wu Wanhong, Yuan Shanshan.(Dept. of Radiology, West China Hospi-tal of Stomatology, Sichuan University, Chengdu 610041, China)

    [Abstract]ObjectiveTo investigate the development of third molars of twelve years old teenagers in Chengdu through X-ray films. MethodsRandomly selected 449 panoramic radiographs of twelve -year -olds from the database of West China Hospital of Stomatology, Sichuan University, and divided the development degree of third molars into several phrases to analysed the development status according to different genders, the left and right sides, the maxilla and the mandible. ResultsMost part of the crowns of the third molars of the twelve years old teenagers were mineralized. There was no significant differences between male and female about the development degree of third molars. Mostly, the development of third molars appeared earlier in the mandible than that in the maxillary. The occurrence ratio was 60.69% on the left side and 64.25% on the right side. The abnormal devel-opment direction of third molar in the maxillary appeared vertical tilting and in the mandible appeared mesial tilting more frequently. ConclusionThe crowns of the twelve-year-olds’third molars were mostly mineralized. The mandible third molars appeared earlier than maxillary ones. ......