成都地区正常恒牙青少年X线片后段牙弓的初步研究

Establishment of Normal Value of Posterior Arch Length of Adolescence in Chengdu

目的 通过对正常恒牙青少年X线片后段牙弓长度的测量及上下第三磨牙发育情况分析 ,为临床判断磨牙位置是否前移以及正畸治疗时推磨牙向后的可能性提供参考。方法 对 81名第二磨牙已萌出的正常青少年 ,平均 (1 2 73± 1 1 9)岁 ,男 4 0名、女 4 1名 ,拍摄X线片并进行头影测量及统计学分析。结果 该年龄段青少年上颌后段牙弓长度男性 (1 6 5 2± 2 35 )mm稍大于女性 (1 6 4 2± 2 5 5 )mm ,但统计学分析无显著性差异。下颌后段牙弓长度男性 (1 3 0 0± 2 4 4 )mm稍大于女性 (1 2 4 3± 2 1 8)mm ,统计学分析同样无显著性差异。上下颌第三磨牙牙胚绝大多数已形成且牙冠已钙化完成 ,其出现率为上颌 84 0 % ,下颌 85 2 % ;下颌牙胚大多为中位前倾方向。

Objective\ To investigate the development of third molar embryo and establish the normal value of posterior arch length of adolescence in Chengdu.Methods\ The samples consisted of 40 males and 41 females with Class 1 dentitions, normal second molar occlusion, no history of orthodontic treatment, and good facial balance. Cephalometry and statistic analysis were conducted for all the subjects.Results\ The normal value of posterior arch length of maxilla in male was(16 52±2 35)mm and in female was(16 42±2 55)mm The normal length of mandible was(13 00±2 44)mm in male and(12 43±2 18)mm in female But statistic analysis showed no gender difference. Most of the third molar embryo had been formed and their tooth crowns had been calcified, the occurrence ratio was 84 0 % in maxilla and 85 2 % in mandible. Most of them located in the middle and inclined mesially.Conclusion\ The data obtained in this study will be valuable for our clinical practice and be helpful for the study concerning dento_facial growth and development.\;