Fig. 4. Reference points and measurements at the sectioned lingual polished surface. (a) the lingual margin of the artificial teeth, (b) the height of the contour at the lingual polished surface, (c) the most inferior lingual border, (A) the perpendicular distance between the a-c line and b, (B) the vertical distance from the occlusal plane to b, (C) the vertical distance between b and c, (D) the vertical distance from the occlusal plane to c, (E) the ratio of C to D, (F) the angle formed by the a-b line and the occlusal plane, (G) the angle formed by the b-c line and the occlusal plane, (H) the angle formed by the a-b line and the b-c line.