Fig. 1

Standardized sagittal section images for a hard tissue and b soft tissue measurements. c Landmarks for the sagittal root angle, between the long axis of tooth and the long axis of the alveolar bone. The red line shows the tooth axis (TA) in the sagittal plane, crossing the incisor and apical points. The white line shows the corresponding alveolar bone axis (BA). To determine BA, a line was drawn joining the palatal and buccal bone crests, with the midpoint defined as A. Another line was drawn parallel to this line, 2 mm apical to the root apex, the midpoint of the labial and palatal surfaces was defined as B. BA is a straight line crossing the two midpoints, A and B. The angle between TA and BA (TA-BA) was measured in degrees. d Dimensions of hard tissue and thickness of labial gingiva measurements. Part 1 was buccal bone and gingiva dimensions, including the thickness of labial gingiva and bone at the CEJ and at levels 2, 4, and 6 mm apical to the CEJ (C-2, C-4, C-6 labial gingiva thickness and C-2, C-4, C-6 buccal bone thickness). Part 2 represented palatal bone dimensions, including the thickness of the palatal bone wall at levels 2, 4, and 6 mm apical to the CEJ (C-2, C-4, C-6 palatal bone thickness). Part 3 represented apical bone dimensions, including the thickness of the labial and palatal bone walls around the apex, measured at the apex and at levels 2 and 4 mm coronal to the apex, respectively (R-0, R-2, R-4 buccal bone thickness and R-0, R-2, R-4 palatal bone thickness). Part 4 represented bone dimensions below the apex, including the length of the root apex to the alveolar palatal plane, measured along the long axis of the anterior tooth (TA-Apex to Palate) and the corresponding alveolar bone axis (BA-Apex to Palate). Part 5 represented root dimensions, including the root diameters measured at levels 2, 4, and 6 mm apical to the CEJ, 2, 4 mm coronal to the apex (C-0, C-2, C-4, C-6, R-2, R-4 root diameter)