The identification ofelectronic surveying lines on 3-D digital models of dentition defects

：Objectives To develop amathematical algorithm and a software package for the process of electronically surveyinga scanned point cloud cast. To provide a principal premise to the subsequent computeraided design and computer aided manufacture (CAD/CAM) of removable partial dentureframework, 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, wascaptured using an optical scanning system with projective grating and high-resolutiondigital camera. Using commercial CAD/CAM software system (Geomagic Studio 6), this pointcloud data was processed and the 3-D digital model of partially edentulous cast wasreconstructed. From a suggested surveying angle the contour points of height wereidentified, and then the digital surveying lines were traced using Projection and ContourExtraction software package. The depth of undercut was measured and defined to determinethe clasp termination of retainer. Results Electronic surveying line of 3-D digitaldentition defect model was achieved. Digital surveying line defined the cast into undercutand non-undercut areas. Different virtualized paths of insertion could be automaticallysuggested when the cast was surveyed and analyzed from different angles. The depth ofundercut was automatically measured and the retentive clasp termination was determined.Conclusions The mathematical algorithm and the software package in this study can be usedto survey and analyze 3-D digital models of dentition defects, and to identify anelectronic surveying line. Key words: Computer-aideddesign;  Denture,partial,removable;  Electronic surveying