Conceptualization, C.C.; methodology, C.C. and T.L; software, P.C. and T.L.; validation, C.C. and P.C.; formal analysis, C.C. and T.L.; investigation, C.C. and T.L.; resources, P.C. and T.L.; data curation, P.C. and T.L.; writing—original draft preparation, C.C. and T.L.; writing—review and editing, C.C., P.C., and T.L.; visualization, C.C.; supervision, C.C.; project administration, T.L. and C.C.; funding acquisition, C.C. All authors have read and agreed to the published version of the manuscript.

Figure 1. Cephalometric measurements. (A) The reference line was the long axis of the tooth. (B) Thicknesses were measured perpendicular to the long axis at 3, 6, and 9 mm apical to the CEJ. Heights were measured parallel to the tooth axis.

Figure 1. Cephalometric measurements. (A) The reference line was the long axis of the tooth. (B) Thicknesses were measured perpendicular to the long axis at 3, 6, and 9 mm apical to the CEJ. Heights were measured parallel to the tooth axis.

Figure 2. Measurements. On the labial side, labial alveolar bone thicknesses C-D, G-H, and L-F; labial cortical bone thicknesses C-D, G-H, and M-F; labial cancellous bone thickness L-M; labial alveolar bone height distance b. On the lingual side, lingual alveolar bone thicknesses A-B, E-F, and I-K; lingual cortical bone thicknesses A-B, E-F, and I-J; lingual cancellous bone thickness J-K; lingual alveolar bone height distance b; and root diameters B-C, F-G, and K-L and total root-bone thicknesses A-D, E-H, and I-F.

Figure 2. Measurements. On the labial side, labial alveolar bone thicknesses C-D, G-H, and L-F; labial cortical bone thicknesses C-D, G-H, and M-F; labial cancellous bone thickness L-M; labial alveolar bone height distance b. On the lingual side, lingual alveolar bone thicknesses A-B, E-F, and I-K; lingual cortical bone thicknesses A-B, E-F, and I-J; lingual cancellous bone thickness J-K; lingual alveolar bone height distance b; and root diameters B-C, F-G, and K-L and total root-bone thicknesses A-D, E-H, and I-F.

Figure 3. CBCT measurements. (A) Tooth orientation of CBCT: The sagittal plane running transversely through the midpoint of the tooth long axis. (B) The sagittal plane was used to measure the thickness and height parameters of all four incisors in each image. (C) On the labial side, labial alveolar bone thicknesses C and G; labial cortical bone thicknesses C and G; labial alveolar bone height b. On the lingual side, lingual alveolar bone thicknesses A and E+F; lingual cortical bone thicknesses A and E; lingual cancellous bone thickness F; lingual alveolar bone height a; and root diameter B and total root-bone thickness D.

Figure 3. CBCT measurements. (A) Tooth orientation of CBCT: The sagittal plane running transversely through the midpoint of the tooth long axis. (B) The sagittal plane was used to measure the thickness and height parameters of all four incisors in each image. (C) On the labial side, labial alveolar bone thicknesses C and G; labial cortical bone thicknesses C and G; labial alveolar bone height b. On the lingual side, lingual alveolar bone thicknesses A and E+F; lingual cortical bone thicknesses A and E; lingual cancellous bone thickness F; lingual alveolar bone height a; and root diameter B and total root-bone thickness D.

Figure 4. Four mandibular incisor roots were sectioned in the transverse plane to illustrate how the reference plane affects the alveolar bone thickness and root diameter. From the CBCT images, the measurements were performed perpendicular to the cut along the long axis (A). From the cephalograms, the measurements were perpendicular to the midline (B). The most prominent points in both labial and lingual aspects which appeared on the image were used for the measurements causing thicker bone and narrower root in the cephalograms.

Figure 4. Four mandibular incisor roots were sectioned in the transverse plane to illustrate how the reference plane affects the alveolar bone thickness and root diameter. From the CBCT images, the measurements were performed perpendicular to the cut along the long axis (A). From the cephalograms, the measurements were perpendicular to the midline (B). The most prominent points in both labial and lingual aspects which appeared on the image were used for the measurements causing thicker bone and narrower root in the cephalograms.

Figure 5. From CBCT. the labial bone height of the mandibular incisor was measured only at the line along the center, whereas from the cephalogram, the occlusal margin of the bone nearby the center of the alveolar crest (arrows) appeared on the film and could be measured.

Figure 5. From CBCT. the labial bone height of the mandibular incisor was measured only at the line along the center, whereas from the cephalogram, the occlusal margin of the bone nearby the center of the alveolar crest (arrows) appeared on the film and could be measured.

Table 1. Comparisons of labial alveolar bone between Ceph, L1CT, and L2CT.

Table 1. Comparisons of labial alveolar bone between Ceph, L1CT, and L2CT.

Labial SideMandibular Teeth
(n = 38)Ceph
(C)L1CT
(L1)L2CT
(L2)ANOVA
p-ValueDifferencesC-L1C-L2L1-L2(1) Alveolar bone thicknesses3 mm apical to CEJ0.64 ± 0.080.48 ± 0.150.41 ± 0.11<0.0010.16 ** ± 0.030.23 ** ± 0.030.07 ± 0.036 mm apical to CEJ0.59 ± 0.180.41 ± 0.130.30 ± 0.17<0.0010.18 ** ± 0.040.29 ** ± 0.040.10 ± 0.049 mm apical to CEJ1.56 ± 0.131.37 ± 0.341.25 ± 0.28<0.0010.19 * ± 0.050.31 ** ± 0.050.12 ± 0.05(2) Alveolar bone height1.03 ± 0.381.49 ± 0.371.51 ± 0.39<0.001−0.46 ** ± 0.09−0.48 ** ± 0.09−0.02 ± 0.09(3) Cortical bone thicknesses 3 mm apical to CEJ0.64 ± 0.080.48 ± 0.150.41 ± 0.11<0.0010.16 ** ± 0.030.23 ** ± 0.030.07 ± 0.036 mm apical to CEJ0.59 ± 0.180.41 ± 0.130.30 ± 0.17<0.0010.18 ** ± 0.040.29 ** ± 0.040.10 ± 0.049 mm apical to CEJ1.56 ± 0.131.37 ± 0.341.25 ± 0.28<0.0010.19 * ± 0.050.31 ** ± 0.050.12 ± 0.05(4) Cancellous bone thicknesses 3 mm apical to CEJ---N/A---6 mm apical to CEJ---N/A---9 mm apical to CEJ---N/A---

Table 2. Comparisons of lingual alveolar bone between Ceph, L1CT, and L2CT.

Table 2. Comparisons of lingual alveolar bone between Ceph, L1CT, and L2CT.

Lingual SideMandibular Teeth
(n = 38)Ceph
(C)L1CT
(L1)L2CT
(L2)ANOVA
p-ValueDifferencesC-L1C-L2L1-L2(1) Alveolar bone thicknesses3 mm apical to CEJ1.05 ± 0.060.79 ± 0.270.89 ± 0.04<0.0010.26 ** ± 0.040.17 ** ± 0.04−0.10 ± 0.046 mm apical to CEJ1.94 ± 0.241.69 ± 0.161.80 ± 0.10<0.0010.25 ** ± 0.040.14 ** ± 0.04−0.11 ± 0.049 mm apical to CEJ2.83 ± 0.052.54 ± 0.252.64 ± 0.08<0.0010.29 ** ± 0.040.19 * ± 0.04−0.10 ± 0.04(2) Alveolar bone height 1.54 ± 0.401.92 ± 0.391.93 ± 0.38<0.001−0.38 ** ± 0.09−0.39 ** ± 0.09−0.01 ± 0.09(3) Cortical bone thicknesses 3 mm apical to CEJ1.05 ± 0.060.79 ± 0.270.89 ± 0.04<0.0010.26 ** ± 0.040.17 ** ± 0.04−0.10 ± 0.046 mm apical to CEJ1.94 ± 0.241.69 ± 0.161.80 ± 0.10<0.0010.25 ** ± 0.040.14 ** ± 0.04−0.11 ± 0.049 mm apical to CEJ2.14 ± 0.211.91 ± 0.351.95 ± 0.27<0.010.23 * ± 0.060.19 * ± 0.06−0.04 ± 0.06(4) Cancellous bone thicknesses 3 mm apical to CEJ---N/A---6 mm apical to CEJ---N/A---9 mm apical to CEJ0.69 ± 0.130.63 ± 0.160.68 ± 0.200.2570.06 ± 0.040.01 ± 0.04−0.05 ± 0.04

Table 3. Comparisons of root diameters and total root-bone thicknesses between Ceph, L1CT, and L2CT.

Table 3. Comparisons of root diameters and total root-bone thicknesses between Ceph, L1CT, and L2CT.

Mandibular Teeth
(n = 34)Ceph
(C)L1CT
(L1)L2CT
(L2)ANOVA
p-ValueDifferencesC-L1C-L2L1-L2(1) Root diameters3 mm apical to CEJ5.52 ± 0.155.75 ± 0.106.00 ± 0.19<0.001−0.23 **± 0.03−0.48 ** ± 0.03−0.24 ** ± 0.036 mm apical to CEJ4.86 ± 0.095.08 ± 0.055.45 ± 0.09<0.001−0.22 ** ± 0.02−0.59 ** ± 0.02−0.37 ** ± 0.029 mm apical to CEJ3.81 ± 0.133.99 ± 0.154.20 ± 0.17<0.001−0.18 ** ± 0.03−0.39 ** ± 0.03−0.21 ** ± 0.03(2) Total root−bone thicknesses3 mm apical to CEJ7.21 ± 0.127.02 ± 0.187.30 ± 0.15<0.0010.19 ** ± 0.04−0.09 ± 0.04−0.28 ** ± 0.046 mm apical to CEJ7.39 ± 0.047.18 ± 0.377.55 ± 0.19<0.0010.22 ** ± 0.06−0.16 ± 0.06−0.37 ** ± 0.069 mm apical to CEJ8.20 ± 0.127.90 ± 0.408.09 ± 0.22<0.0010.30 ** ± 0.060.11 ± 0.06−0.19 * ± 0.06