正常下颌第二前磨牙牙冠轴面外形与牙龈外形的几何关系

目的 探讨正常牙冠轴面外形与其周围健康牙龈外形的关系。方法 以下颌第二前磨牙为研究对象，在牙列模型上通过牙冠部、牙龈作３个纵断面，用曲线拟和方法得到每个断面的牙齿轴面外形及相应牙龈外形的曲线方程，以此分析两者之间 关系并计算牙冠起始外形角度，即倒凹程度的大小。结果 不同个体的牙冠轴面外形和牙龈外形有其特定的几何关系，同一断面的牙冠轴面外形曲线对应特定的牙龈外形曲线。同名牙同一断面的牙冠轴面外形之间

Geometric relationship of axial crown contour and gingiva contour of normal second mandibular premolars

OBJECTIVE: To investigate the relationship of axial crown contour and surrounding healthy gingiva contour. METHODS: Mandibular second premolars were selected as the object of study. Three cross-sections were made through crown and gingiva of the model tooth. Curve functions of axial buccal crown and gingiva contour of each section were acquired by means of curve fitting, and the angle of emergence profile was calculated, which represents the degree of undercut. RESULTS: There is unique relationship between axial crown and gingiva contour individually. This character of tooth is similar to its contralateral tooth. The emergence profile angles are in the range of 40 degrees-110 degrees, 84.1% of the angles are in range of 70 degrees-110 degrees, 15.9% in 40 degrees-70 degrees, that is to say natural teeth are inclined to be of less undercut. CONCLUSION: The geometric relationship between crown contour and gingiva contour is so characteristic that contralateral tooth should be the only guidance to replace lost tooth.