Figure 2.

Definition of a 3D virtual global reference frame (GRF) using multiplanar reconstruction (MPR) and the two-dimensional (2D) on-screen Cartesian coordinate system (CCS). MPR adds a third dimension (z-axis) to the x- and y-axis of the 2D CCS (corresponds to the x- and y-axis in b). The axes were set orthogonal (90° offset) in all three dimensions, which resulted in a sagittal (A,D), transversal (B,E), and coronal (C,F) section plane view. Initially the axes were rotated until the sagittal z-axis (A) and transversal (B) and coronal x-axes (C) matched the horizontal x-axis of the on-screen CCS. The sagittal axes (orange) were orthogonal to this (B,C). For maximal standardization of object orientation, the object was first aligned along the axes of the transversal (B) and coronal (C) section planes using some symmetry planes (dotted lines). Subsequently, the region of interest has been enlarged [(D–F), zoom factor 1.7]. The sagittal axes (orange) were translationally moved off from the median plane to the right side (E) and rotated (F) until the tooth 101 appeared in the sagittal plane view (D). There the object was rotated along a laterolateral axis until the incisor occlusal table (IOT; see insert) hits the coronal z-axis (red). Object alignment was rechecked. To create a GRF for single tooth reconstruction, the object was then spatially fixed within the coordinate system by avoiding rotation and translation of the object as well as rotation of orthogonal axes in the sagittal and transversal view. R, right; L, left; D, dorsal; V, ventral, Ro, rostral; Cd, caudal.