Figure 4.

Determination of IIA by cephalometric definition of the labial axis of opposing permanent and deciduous incisor clinical crowns (LACC) and the lingual and palatal clinical crown border reference axes (LPB) for permanent third incisor teeth. (A,B) LACC reconstructions required definition of certain dental landmarks starting with the sagittal occlusal center (SOC). The SOC was determined by bisecting the occlusal surface of individual incisors (inserts). For that purpose, PixelStick endpoints (yellow) were positioned to the most labial (circle endpoint) and palatal or lingual (diamond endpoint) occlusal points. The SOC was thus automatically ascertained by the ruler instrument. Subsequently, endpoints were positioned to connect the SOC and palatal or lingual alveolar margin (AM) of permanent incisors and palatal or lingual crown neck of deciduous incisors (inserts). A line perpendicular to the SOC-AM line and the AM point, in turn, defined the apicolabial reference point (ALRP) at the intersection with the labial tooth surface. For scans that reveal the gingival margin (inserts; arrow heads), the ALRP always appeared close or superposed to it. The respective occlusolabial reference point (OLRP) was defined as the most labial occlusal point. Connection of ALRP and OLRP resulted in the respective LACC (red line) for each incisor. IIA was defined as the angle enclosed by the LACC of opposing incisors. (C) The angle enclosed by the adopted lingual and palatal reference axes of third incisor teeth was determined (red lines; arrows). All angles were measured using the angle measuring capabilities of PixelStick. A, 101:401; B, 501:801; C, 103:403; labial, left; lingual or palatal, right.