PURPOSE: To provide the extracting method for a margin line for considering the CAD/CAM conversion for manufacturing a crown and deciding easily the margin line by deriving a variation from data for showing a shape of a supporting base tooth, extracting a sequence of points which can be decided to be a margin part and determining the margin line.
CONSTITUTION: First of all, by measuring a shape of a plaster model of a supporting base tooth, shape data of the supporting base tooth is obtained. Subsequently, an intersecting line 23 of a plane containing a central axis 22 of a three-dimensional shape 21 of the supporting base tooth and the curved surface for forming the supporting base tooth shape 21 is considered, and a distance between each point on the intersection line 23 and the central axis 22, and an inclination of each adjacent point are calculated. As a result, a point in which the inclination crosses 'O' or a point in which a variation of the inclination becomes larger than a certain value becomes a margin part. Subsequently, a calculation is repeated with regard to the intersecting line to the respective planes and a sequence of points of the margin part is obtained. Next, this sequence points is displayed on a display device, and based therein, a margin line is determined.
Katsuya Miyoshi
Masami Baba
