In conjunction with the recent development of CAD technology and computer graphics, the laser scanning technique has been applied in the field of dentistry to obtain 3D information from dental models because of high-speed processing and high accuracy. Recently, in order to obtain more accurate data on dental cast surface, a novel special dental model laser scanning system has been designed, which is completed by rotating the horizontal disk and vertical disk. This scanning system with 2 axes can minimize the blind area brought by the dental cast surface’s irregularity, and compared with the previous 3 axes scanning system, its structure is simpler and its cost less. Based on the feature of scanning data obtained by the special dental cast laser scanning system, we present a sequence of new algorithms for measuring and analyzing dental model.

In general, the dental model surface consists of three hundred thousands’ triangle faces, and the vertexes of these triangles are not distributed on regular mesh. In computer-aided measuring and analyzing system in orthodontics, most operations such as intersection algorithm, model measuring, tooth extraction, and collision detection, are all done on the triangle faces, thus, how to organize the triangle faces efficiently is a key point. Here we present an approach to organizing and indexing triangle faces with regular mesh, which provides us a good way to solve the problem.

It is a basic interactive operation to pick up a point on dental model surface, i.e., obtain three-dimensional coordinate of a point, which is indispensable for measuring dental model. This operation is essentially equivalent to an intersection algorithm between a line and all the triangle faces on the surface. Based on the aforementioned mesh index way, we propose a fast, stable and real time intersection algorithm.

With the above intersection algorithm, users, by using 2D mouse, can get the 3D coordinates of any points on the dental surface, so they can calculate straight line distance of two points and the separation angle between two lines easily. They can also calculate curvilinear distance along dental surface between two points and surface area on the dental model surface.

We develop a computer-aided reconstructing and measuring system in orthodontics in PC environment by using our presented algorithms. Its main modules include: 1) Reading and preprocessing of laser scanning data; 2) 3D reconstruction and display; 3) Model measuring and the measured data storage. Besides, some other modules such as tooth operations and collision detection between the upper jaw and the lower jaw are also included in the system. The system has been used in Peking University of School of Stomatology.

This work offers a good instance for CAD technique in medicine field.