Fig. 2

Representative images presenting the protocol of measurement. The correlated planes were determined by 3 intersected guidelines with different colors, which are blue for an axial plane, red for a sagittal plane, and green for a coronal plane. A Adjust the location of the axial plane by passing the blue guideline through the CEJ of the selected tooth in both the coronal and sagittal views, then rotate the green guideline until the intersecting line is the shortest. B Rotate the red guideline until it passes through the root apex and the midpoint of the incisal margin. C Rotate the green guideline until it passes through the root apex and the cusp. D Variables measured in CBCT in the sagittal plane. 1. LABA, the blue alveolar bone area of the labial side of the sagittal plane of the 6 mandibular anterior teeth. 2. vertical alveolar bone loss (CEJ-crest, the distance from the cementoenamel junction of the 6 mandibular anterior teeth to the alveolar bone crest measured on the sagittal plane); B, labial bone loss; L, lingual bone loss. 3. R, root length (distance from the cementoenamel junction of the 6 mandibular anterior teeth to the root apex, measured parallel to the long axis of the tooth on the sagittal plane); 4. upper (D1), middle (D2), and lower (D3) alveolar thicknesses (labial alveolar thickness on the sagittal plane as a distance from the root surface of the 6 mandibular anterior teeth to the labial surface of the alveolar bone, measured perpendicular to the long axis of the tooth at 3 mm, 6 mm, 9 mm below the CEJ)