影响曲面断层片上颌尖牙长轴角度的部分因素分析

The analysis of factors affecting the canine angulation in panoramic radiograph

目的 研究上颌尖牙区三维方向上多种因素变化对曲面断层片中牙长轴角度影响.方法 用干颅骨标本、模型牙制作模型模拟拔牙矫治后理想牙颌状态,从初始状态开始,依次改变右上尖牙的轴倾度、右上尖牙的转矩、上颌右侧弓形以及曲断选层位置,并在精确定位状态下分别拍摄颅骨模型的曲面断层片,测量右上尖牙牙长轴影像与固定参照平面的夹角.结果 尖牙实际轴倾度与曲断片牙长轴角度呈同方向变化;尖牙根颊向转矩使牙根影像趋于后倾,根腭向转矩使牙根影像趋于前倾;弓形尖圆时牙根影像趋于前倾,弓形方圆时牙根影像趋于后倾;选层位置靠后时牙根影像趋于前倾,选层靠前时牙根影像趋于后倾,二者相差1.8°.结论 曲面断层片所示的牙齿长轴角度受局部多种三维因素的共同影响,且具有一定的规律性.

Objective To examine the effect of variable 3D factors of maxillary teeth position on the angulation of the canine axis in panoramic image. Methods A dry skull and a set of model teeth served as the typodont testing device to simulate the ideal occlusion after orthodontic treatment with four premolars extraction. The tip and torque of the upper right canine, the archform of the righ tdental arch and the position of the focal trough were altered in sequence, and panoramic films at each status were taken. The angulations of maxillary canines in each film were measured. Results The true tip of the upper canine and its image angulation in panoramic changed by the same direction. As the root buccal torque increased, the root image tilt distally. As the archform and the position of the focal changed, the angulations of the tooth image were distorted relatively, and the difference was as big as 1.8°. Conclusions The angulations of the long axis of teeth in panoramic images wereimpacted by a series of local 3D factors, and some laws were found about their relationship.