Orthlieb J D
Cranio. 1997 Oct;15(4):333-40. doi: 10.1080/08869634.1997.11746028.
The tangent law explained the sagittal organization of the mandibular teeth by geometrical analyses. According to this concept, the long axis of all mandibular teeth must converge at one point in the circle of the "curve of Spee", and this point is diametrically opposed to the condylar point. A cephalometric analysis of 470 patients was the basis for this statistical study of the radius of the curve of Spee. The mean radius was approximately 80 mm. The mandibular incisors followed the tangent law, but the long axis of the posterior mandibular teeth exhibited a progressive differential angle (postero-anterior) with the direction of the tangent (15 degrees, 20 degrees, 25 degrees, 28 degrees). This differential angle generates a horizontal strength component with tendency to forward tooth movement, tightening of the proximal contacts. The use of this cephalometric reference could help the dentist to determine a more suitable organization of the occlusion in the sagittal plane.
正切定律通过几何分析解释了下颌牙齿的矢状排列。根据这一概念，所有下颌牙齿的长轴必须在“司皮曲线”的圆周上汇聚于一点，且该点与髁突点相对。对470例患者的头影测量分析是这项关于司皮曲线半径的统计学研究的基础。平均半径约为80毫米。下颌切牙遵循正切定律，但下颌后牙的长轴与切线方向呈现出逐渐增大的差异角度（后 - 前）（15度、20度、25度、28度）。这种差异角度产生一个水平力分量，有使牙齿向前移动、收紧邻面接触的趋势。使用这种头影测量参考可以帮助牙医在矢状平面上确定更合适的咬合排列。
