牙列缺损模型三维数字化观测线的确立

The identification of electronic surveying fines on 3-D digital models of dentition defects

目的探索一种基于三维点云模型获取三维数字化观测线的计算方法，开发自动提取三维数字化观测线的软件，为提高模型观测的客观性和精确度、实现应用计算机辅助设计（CAD）与计算机辅助制作（CAM）技术完成可摘局部义齿修复奠定基础。方法以Kennedy第二类第二亚类牙列缺损为研究对象，光栅扫描法采集石膏模型的三维点云数据，在Geomagic Studio6通用CAD—CAM软件中进行数据处理和三维重建。通过本项实验开发的投影轮廓提取法软件，计算观测方向上的最大轮廓曲线，测量倒凹深度，确定并标记卡环固位体卡臂尖的位置。结果得到牙列缺损模型的三维数字化观测线；该观测线将倒凹区和非倒凹区明确分开，可从各个方向观察和分析模型，判定相应的义齿就位道；自动测量倒凹深度，确立并标记固位臂卡臂尖的位置。结论应用该计算方法和软件初步实现了牙列缺损三维模型的数字化观测和分析。

Objectives To develop a mathematical algorithm and a software package for the process of electronically surveying a scanned point cloud cast. To provide a principal premise to the subsequent computer aided design and computer aided manufacture （CAD/CAM） of removable partial denture framework, and to provide a method to improve quality control in the dental laboratory. Methods Point cloud data of a partially edentulous cast, a mandibular Kennedy Class Ⅱ Modification 2 arch, was captured using an optical scanning system with projective grating and high-resolution digital camera. Using commercial CAD/CAM software system （Geomagic Studio 6）, this point cloud data was processed and the 3-D digital model of partially edentulous cast was reconstructed. From a suggested surveying angle the contour points of height were identified, and then the digital surveying lines were traced using Projection and Contour Extraction software package. The depth of undercut was measured and defined to determine the clasp termination of retainer. Results Electronic surveying line of 3-D digital dentition defect model was achieved. Digital surveying line defined the cast into undercut and non-undercut areas. Different virtualized paths of insertion could be automatically suggested when the cast was surveyed and analyzed from different angles. The depth of undercut was automatically measured and the retentive clasp termination was determined. Conclusions The mathematical algorithm and the software package in this study can be used to survey and analyze 3-D digital models of dentition defects, and to identify an electronic surveying line.