Fig. 4
The detailed protocol of A, B angle measurements. Creating local 3D reference frames, the correlated planes were determined by intersected guidelines with different colors, which were red for axial planes, green for sagittal planes, and orange for coronal planes. A WP-based reference frame. Take WP as horizontal plane, project the bony WALA ridge marks of the first and second molars on the horizontal plane, connect the two points as WLp, make the sagittal plane through WLp and perpendicular to the horizontal plane, and make the coronal plane through one mark and perpendicular to the horizontal plane and sagittal plane. B OP-based reference frame. The method was the same as A, and the two landmarks were replaced by the mesial buccal cusp of the first and the second molars. C Mesiodistal angle (A angle): Find the sagittal section of the longest tooth axis of M3 and record the angle between this axis and the horizontal plane in the sagittal plane; labiolingual angle (B angle): Find the coronal or horizontal section of the longest tooth axis of M3, record the angle between this axis and the sagittal plane in the coronal or horizontal plane