The 3D volumetric model of a tooth is constructed based on the image data of CT cross-section layers.Each cross-section image

whose interval is 0.5mm and thickness is 1mm

is treated by two-value conversing

boundary extracting and boundary key points selecting.With the boundary key points of four neighborhood layers

three-dimensional solids between the two adjacent layers are produced according to 3D-Delaunay tetrahedron algorithm.Its validity of each solid element is checked if their internal products between the estimated outward normal vector and the vector from sphere center to vertex are all positive or not.All obtained valid 3D solid elements are combined with Boolean operation

and the volumetric model of a tooth is then achieved at last.This approach is proved to be simple and effective with a tooth sample.