牙列缺损数字化模型观测方法初探

Electronic surveying of digital partially dentate casts

目的探索牙列缺损数字化模型的观测方法，为下一步计算机辅助设计（CAD）可摘局部义齿支架奠定基础。方法三维点激光扫描仪采集牙列缺损石膏模型的三维点云数据，在国产三维CAD软件唐龙系统中进行数据处理和三维重建。以唐龙系统为平台，用C＋＋语言开发“模型观测”功能模块。在点云中心建立垂直于袷平面的中心轴，以10°为单位，将周围点云围绕中心轴等分为多个区域，通过计算每个区域内点云距中心轴的距离，得到颊、舌侧外形高点，分别连接每个区域颊侧及舌侧外形高点，得到以中心轴方向为就位道的观测线。通过调整中心轴角度得到不同的观测线。唐龙系统在生成观测线的同时自动标示倒凹区，并测量倒凹深度，通过将外形高点线沿就位道方向向倒凹区延伸完成去除倒凹的功能。结果在计算机中绘制出牙列缺损数字化模型的观测线，确定了倒凹区及倒凹深度，并可完成去除倒凹的操作。数字化模型的观测线与传统方法在石膏模型上绘制的观测线形态相似。结论基于唐龙系统开发的“模型观测”模块可实现对牙列缺损数字化模型的观测，操作简便，可在此模块基础上进一步进行可摘局部义齿CAD。

Objective To develop a method of surveying the digitalized partially dentate cast in order to accomplish computer aided design （CAD） of removable partial denture （RPD） frameworks. Methods The stone cast of a partially dentate patient was scanned using a three-dimensional laser scanner. Points on the surface of the digitalized cast, termed as a ＂point cloud＂ , were obtained. The point cloud was then imported into self-developed Tanglong software to sample and uniform. New module of identifying the surveying lines was specially written in Tanglong using C ＋ ＋. A straight line was created in the center of the cloud point. Then the cloud point surrounding the straight line was divided into many parts. Local coordinates were established to indicate the information of angle and distance of every point to the straight line. Surveying lines were produced step by step electronically by identifying the closest and farthest points relative to the straight line and then connected together. Different surveying lines were obtained by adjusting the angle of the straight line. After the surveying lines were decided, the undercut areas could be marked and the depth of undercut was calculated automatically. The blockout of the undercuts could also be achieved by moving the location of the point cloud in undercut area. Results Survey lines of digitalized partially dentate casts were generated in computer. The undercut area and its depth were identified and the undercut could be blocked out. The shape of survey lines on the digitalized casts was similar to that on the physical casts drawn using traditional method. Conclusions The new module in Tanglong software was developed specifically for surveying partially dentate casts. It had a user-friendly interface with the easy-to- understand menus. The success of surveying dental casts digitally would make it possible to CAD of RPD frameworks.