The Preparatory Research To Spherical Relationship Of Chinese Occlusal Surface On CT Three-dimensional Model

We tend to use more and more CT three-dimensional model for its property of objectivity. Moreover, the CT three-dimensional model is one of the ways to take three dimensional measurements. This article examines the spherical relationship of Chinese occlusal surface on CT three-dimensional model. The purpose of this research is to establish a method of three-dimensional measurements in the future.The paper mainly includes discussions concerning the spherical relationship of Chinese occlusal surface. Firstly, we get a new method of aided identifying landmark on CT three-dimensional model. With this method, we can precise identify landmark of occlusal surface. Experiments prove this spherical relationship to be true by using the definition of the sphere. The center of a sphere is the point of crista galli. Finally, we made a measurement of a canted occlusal plane with the theory of spherical relationship. The results indicate the initial value of the spherical relationship. The whole paper divided to three parts:1. Aided identifying landmark of the complicated structure of occlusal surface on CT three-dimensional model. We introduce a new method of aided identifying landmark in experiment 1. It is the foundation for three-dimensional measurements. The method of direct identifying landmark on three-dimensional model may lead to the hard identifying and the waste of time because of the influence of visual perspective. These reasons become the problems of the three-dimensional measurements. In order to resolve the problem, after the CAD (Computer-aided design) point coincident with the common landmark,we acquired the coordinate of common landmark by reading the coordinate of CAD point. This method made the three-dimensional identifying landmark to become two-dimensional identifying landmark. The aided identifying landmark method can identify the complicated structure such as the occlusal cusp in intercuspal position. The error is less than 0.2 millimeter. The aided identifying landmark method is easy to learn and the reliability is good.2. The preparatory research to spherical relationship of Chinese occlusal surface. When we find the center of occlusal sphere is behind the original point, we suggest that the center of occlusal sphere is the point of crista galli. Experiments prove this spherical relationship to be true using the definition of the sphere. The differences of distance between crista galli and the occlusal cusps are less than 0.9mm. It is acceptable in clinical. This means that the differences of distance between crista galli and occlusal cusps are small. So we can consider it as sphere. In a word, the occlusal surface forms the occlusal sphere. 3. The application of occlusal sphere--the measurements of the canted occlusal plane. The occlusal sphere is with features of three-dimensional measurements. With this theory, we made a measurement of the canted occlusal plane. The experiment's results indicated that we can measure every tooth. It is more precise than measurements of'occlusal plane'. So we made the two-dimensional measurements of occlusal plane to three-dimensional measurements. Finally, the experiment indicated the initial value of the occlusal sphere theory.The whole paper discusses the spherical relationship of the occlusal surface. Moreover, we bring up a precise method of aided identifying landmark on three-dimensional model. Finally we prove the initial value of spherical relationship.