下颌无牙颌牙槽嵴牙位划分方法的初步探讨

A preliminary study on division method of teeth position in the edentulous mandible alveolar ridge

目的:初步探讨下颌无牙颌牙槽嵴牙位划分方法,为测量分析下颌牙槽嵴形态及其对义齿稳定影响提供定位依据。方法:收集符合标准的下颌无牙颌患者模型302例,从中随机选取50例,通过三维激光扫描获取石膏模型牙槽嵴表面数据,运用Solid Works软件确定咬合平面、并在牙槽嵴顶线的投影上利用各天然牙中点至中切牙近中面长度占同侧天然牙列近远中长度(正中切牙近中面至第二磨牙远中面)的百分比值确定各牙位,标记并连接各测量点:牙槽嵴顶中央点投影(A),左侧磨牙后垫前缘投影(L),右侧磨牙后垫前缘投影(R),左右磨牙后垫前缘投影连线(L R)的中点(M),连接A、M并标记AM中点C;连接C到各牙位中点标记点,并连接M到后牙区各牙位中点标记点,测量各连线与AM的夹角;统计分析测量的数据。结果:在前牙区,C点到各个牙位中点连线近似位于同心圆上,连线与AM的夹角稳定性高(C.V<5%);在后牙区,M点到各个牙位中点连线与AM的夹角较C点连接角度的方差和极差更小,稳定性更高(C.V<5%);同时,利用AM与LR的比值作为定位角度参数建立预测方程,可有效较正各牙位定位偏差。结论:选择下颌牙槽嵴中央线上不同的牙位划分线原点,使用划分线与矢状线的夹角平均值,并通过咬合平面上牙槽嵴顶线投影的高宽比作为参数建立牙位划分角度预测方程,可在下颌牙槽嵴顶线上较稳定地划分各牙牙位。

Objective： To investigate the method of dividing the mandibular alveolar ridge into each tooth position, and provide a basis of tooth positing method for morphometric study of mandibular alveolar ridge. Methods： in this study, 50 cases were randomly selected from 302 cases of standard model of mandibular edentulous patients. The alveolar surihce data of plaster models were collected by three-dimensional laser scanning, and the occlusal plane was determined by using the SolidWorks software. On the projection of alveolar ridge line, each tooth position was determined by the percentage values of length of natural tooth midpoint to central incisor mesial surface accounted for unilateral side natural dentition mesiodistal length（central incisor mesial surface to second molar distal surface）, the measuring points were marked and connected as follows： ① LR was defined as connecting line of the projection of left apex of the retromolar pad （L） and projection of right apex of the retromolar pad （R） whose midpoint was labeled as M, AM was defined as the line connecting the projection of alveolar ridge crest central point （A） and M, C was labeled as midpoint of AM; ②Connected C to the midpoint of each tooth, and connected M to the posterior region of each tooth midpoint, measuring the angles between each connection and AM. Statistical analysis were followed. Results： In the anterior region, the connecting line of C to midpoint of each tooth was approximately located on the concentric circle, high stability of the angles were observed （CV〈5%）; In the posterior region, the angle between the connecting line of M to midpoints of each tooth and AM showed smaller variance, range and higher stability than the angle between the connecting line C to midpoints of each tooth and AM （CV〈5%）; Meanwhile, the ratios of AM and LR could be used as the division angle to establish the predictive equation, and to correct teeth positioning deviation effectively. Conclusion： By choosing different origins of division line in the sagittal line of mandibular alveolar ridge, teeth position can be divided in the mandibular alveolar crest line using the included angle of division line and sagittal line on average value. And the aspect ratio of alveolar crest line in the occlusal plane can be used as a parameter to establish prediction equations for division angle of tooth position.