Measurements of the angles. (A) Measurement of the angle between the axis connecting the apex and the cusp tip of the mandibular first premolar and the true vertical. As can be observed, sections were made buccolingually, and the section pertaining to the mesiodistal width of the tooth was used. (B) Measurement of the labial surface curvature. The arrow indicates the axis connecting the cusp tip to the apex. The horizontal lines are 0.5 mm apart. The measurement of the angle is performed between the axis of the tooth and tangents drawn at the intersection of the horizontal lines and the labial surface.