Introduction
This retrospective study aimed to evaluate the morphology of the alveolar bone and to assess the incidence of fenestration and dehiscence during presurgical orthodontic decompensation in patients with skeletal Class III malocclusion.
Methods
The study included 60 patients with skeletal Class III high-angle malocclusion who had completed presurgical orthodontic treatment. Lateral cephalograms and cone-beam computed tomography images were obtained before (T0) and after (T1) the presurgical orthodontics. The labial inclination angles of the mandibular central incisors were measured using lateral cephalograms. Cone-beam computed tomography images evaluated alveolar bone thickness and height along the roots of the target teeth and assessed the incidence of fenestration and dehiscence. Statistical analyses were conducted using paired t tests, chi-square tests, and binary logistic regression.
Results
From T0 to T1, decompensatory movements of the mandibular central incisors resulted in a reduction in alveolar bone thickness and vertical height. Most teeth exhibited bone loss of 2 mm apical to the cementoenamel junction. The prevalence of labial bone defects increased significantly, rising from 51.7% to 73.3% in the mandibular left central incisor and from 51.7% to 76.7% in the mandibular right central incisor. Greater decompensation angles were linked to higher risks of fenestration and dehiscence at T1. When the probability of bone defect occurrence was set at 50%, the thresholds for changes in the IMPA and L1-NB were found to be 5.47° and 5.91°, respectively.
Conclusions
The threshold for decompensation of the mandibular central incisors is relatively low in patients with skeletal Class III high-angle because of the anatomically thin alveolar bone. Exceeding this threshold increases the risk of bone defects. Therefore, careful evaluation of the periodontal condition is essential when establishing treatment objectives to prevent adverse periodontal outcomes.
Highlights
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Presurgical treatment can lead to a reduction in alveolar bone thickness in this study.
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The incidence of alveolar bone fenestration and dehiscence also increased.
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Patients in this study have a restricted range for mandibular incisor decompensatory movement.
Skeletal Class III malocclusion is a prevalent clinical condition, with a reported prevalence of 15.69% in the Chinese population. Research indicates that 36% of patients with skeletal Class III malocclusion undergoing early treatment require additional surgical intervention. Comprehensive management typically involves orthodontic-orthognathic treatment, which consists of 3 phases: presurgical orthodontic decompensation, orthognathic surgery, and postsurgical orthodontics. , Presurgical decompensation includes the retraction of labially inclined maxillary incisors and labial movement of lingually inclined mandibular incisors to correct their axial inclinations.
The extent of presurgical orthodontic decompensation directly affects bone segment movement during orthognathic surgery. Insufficient preparation of the incisors can adversely affect surgical outcomes and postsurgery alignment, often leading to suboptimal skeletal improvements in orthognathic surgery patients. ,
Compared with other malocclusion types, patients with skeletal Class III high-angle malocclusion typically have the thinnest alveolar bone in the anterior mandibular region. , Substantial decompensation during presurgical orthodontics, influenced by both anatomic limitations and iatrogenic factors, can lead to alveolar bone resorption and undesirable periodontal outcomes, including fenestration and dehiscence. However, the optimal level of decompensation required to achieve favorable surgical results while maintaining the stability of the alveolar bone remains debated. ,
This study assessed the morphology of the alveolar bone around the mandibular central incisors before and after presurgical orthodontic treatment in patients with skeletal Class III high-angle malocclusion. It evaluated the incidence of alveolar bone defects and examined the relationship between these changes and the degree of presurgical orthodontic decompensation. Furthermore, the study explored the periodontal limits of decompensation and proposed guidelines for establishing presurgical orthodontic objectives in patients with skeletal Class III malocclusion.
Material and methods
This study recruited 60 patients with skeletal Class III high-angle (18 males and 42 females, with a mean age of 24.66 ± 4.75 years) who completed presurgical orthodontic treatment at Tianjin Stomatological Hospital between June 2019 and October 2023. The patients met the inclusion and exclusion criteria ( Table I ). A total of 120 mandibular central incisors (left and right) were evaluated. The average duration of presurgical orthodontic treatment was 16.77 ± 8.68 months. Sample size estimation was performed using G∗Power software (version 3.1.9.7; Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany). The analysis indicated that 34 samples were necessary based on an effect size of f = 0.5, a significance level of α = 0.05, and a statistical power of 0.8. The study was approved by the Ethics Committee of Tianjin Stomatological Hospital (approval code: PH2024-Q-013).
Table I
Inclusion criteria and exclusion criteria
| Inclusion criteria | Exclusion criteria |
|---|---|
| 1. Skeletal Class III malocclusion: ANB <−3° | 1. Missing or malformed mandibular anterior teeth |
| 2. Bilateral molar angle Class III relationship | 2. History of previous orthodontic or orthognathic treatment |
| 3. High-angle: SN-MP >37.7°; FH-MP >32.0°; FHI ≤62% | 3. History of endodontic treatment or restorations on the mandibular central incisors |
| 4. Mandibular dental arch crowding: <3 mm and not concentrated in the central incisors (mild crowding) | 4. History of periodontal surgery |
| 5. Healthy periodontium with no significant horizontal or vertical bone resorption | 5. Severe facial asymmetry, craniofacial syndromes, and cleft lip or palate |
| 6. Orthodontic treatment plan: straight-wire fixed appliances (0.022-in MBT prescription appliance) |
Cone-beam computed tomography (CBCT) scans and lateral cephalograms were obtained before (T0) and after (T1) presurgical orthodontic decompensation, using a KaVo 3DeXam system (120 kV, 10 mA, 17.8 seconds, 0.3 mm voxel). The T1 CBCT imaging data were typically recorded 1 week before orthognathic surgery. During imaging, patients were seated naturally and instructed to occlude in maximal intercuspation. CBCT data were exported in digital imaging and communications in medicine format and imported into Dolphin Imaging software (version 11.8; Dolphin Imaging and Management Solutions, Chatsworth, Calif). A 3-dimensional (3D) reconstruction of CBCT data was performed to obtain coronal, sagittal, and axial views. Lateral cephalograms were also imported into the software to facilitate more precise identification of landmarks.
A schematic diagram of the cephalometric landmarks is shown in Figure 1 . The following variables were evaluated: ANB (°), SN-MP (°), FH-MP (°), FHI (S-Go/NMe, %), IMPA (°), and L1-NB (°). In this study, changes in IMPA and L1-NB were used to indicate the decompensation of the mandibular central incisors. The labiolingual movement of the mandibular central incisors and the alveolar crest at T0 and T1 was measured on lateral cephalograms ( Fig 2 ). The horizontal reference plane (HRP) was established by rotating the SN plane clockwise by 7° through point S. The vertical reference plane (VRP) was defined as a plane perpendicular to the HRP and passing through point S. The distances from the VRP to the incisal edge, the root apex, and the labial and lingual alveolar crests were measured.
Cephalometric landmarks. N, nasion; S, sella; P, porion; Or, orbitale; A, subspinale; B, supramental; Go, gonion; Me, menton; L1-Tip, mandibular central incisor; L1-Root, root apex of mandibular central incisor.
Reference planes and variables of position measurements of the mandibular central incisors. Reference planes: HRP , a horizontal plane at an angle of 7° clockwise to the SN plane passing through Sella; VRP , plane perpendicular to the HRP passing through point Sella. Measurement variables: edge-VRP , the distances from the VRP to the incisal edge; li-VRP , the distances from the VRP to the lingual alveolar crests; la-VRP , the distances from the VRP to the labial alveolar crests; edge-VRP, the distances from the VRP to the root apex.
After importing CBCT data, alveolar bone thickness and vertical height were assessed at specific intervals along the maximum labiolingual diameter of the designated tooth. To obtain the target axial slice, the blue lines on the coronal and sagittal views were aligned with the cementoenamel junction (CEJ). Subsequently, the intersection of the red and green lines was positioned at the center of the pulp chamber at the incisal plane of the designated tooth. The image was rotated until the red line passing through the tooth represented the shortest distance. In the sagittal view, the green line was adjusted to align with both the root apex and the midpoint of the CEJ. Finally, in the coronal view, the red line was positioned through the midpoint of the incisal edge and the root apex, thereby generating the desired slice. Using the 2-dimensional line module, alveolar bone thickness was measured at 2, 5, and 7 mm apical to the CEJ, as well as at the root apex. Figure 3 , A and B illustrates the measurement planes of the mandibular central incisors before and after presurgical orthodontic treatment. In addition, the vertical attachment level of mandibular central incisors was assessed ( Fig 4 ).
Measurement planes of the target teeth: A, T0; B, T1.
Marker points and measurement variables. ABH , alveolar bone height (distance between CEJ and crest of alveolar ridge); ABT , alveolar bone thickness; la , labial side; li , lingual side.
A bone cortical defect more than 2 mm from the alveolar crest to the CEJ in the CBCT coronal section was classified as dehiscence. ,, A defect not involving the alveolar crest was classified as a fenestration. The dehiscence and fenestration constitute alveolar bone defects. , The integrity of the buccal and lingual alveolar bone was assessed through the axial and cross-sectional slices of each mandibular central incisor. An alveolar bone defect was confirmed when the cortical bone was absent around the root in at least 3 consecutive views.
Statistical analysis
All samples were remeasured by the same examiner after a 2-week interval. The intraclass correlation coefficient exceeded 0.9, indicating high reproducibility. Intraobserver agreement in the diagnosis of dehiscence and fenestration was evaluated using kappa statistics, with the following interpretive scale: κ ≤0.20, poor; κ = 0.21-0.40, fair; κ = 0.41-0.60, moderate; κ = 0.61-0.80, good; κ = 0.81-1.00, very good.
This study employed the Dahlberg formula (e = √ [Σd 2 / 2n]) to determine the absolute method error. Random measurement errors were assessed using Bland-Altman plots. An independent t test was conducted to analyze gender differences, whereas paired t tests compared alveolar bone morphology between T0 and T1. Chi-square tests were used to evaluate the incidence of fenestration and dehiscence before and after treatment and by gender. Pearson correlation, linear regression, and binary logistic regression were used to assess the relationship between mandibular incisor decompensation and changes in alveolar morphologic bone. A significance level of α = 0.05 was adopted for all statistical tests.
This study analyzed 120 mandibular central incisors (from 60 patients, bilaterally) to identify risk factors associated with alveolar bone dehiscence and fenestration during orthodontic treatment. Generalized estimating equations accounted for within-patient clustering using patient ID as the cluster variable. An exchangeable correlation structure was assumed (constant intrapatient correlation), with robust standard errors (Huber-White estimator). Fixed effects (treatment duration, basal cortical bone thickness, and sex) were reported as β coefficients (95% confidence interval [CI]) for population-averaged effects. Analyses used R software (R Core Team, Vienna, Austria) (α = 0.05).
Sensitivity analyses using alternative correlation structures (unstructured or AR1) confirmed robust treatment duration effects (β = 0.12 [95% CI, 0.05-0.19], P <0.001). An intraclass correlation coefficient of 0.18 indicated moderate within-patient correlation, supporting generalized estimating equations adjustment.
Results
The kappa value for interobserver agreement was 0.791, indicating good reliability for this method. The Dahlberg formula calculated absolute measurement errors at each site ranged 0.13-0.21 mm, with all errors being below 0.3 mm. This falls within the threshold recommended by Houston for alveolar bone measurements. Bland-Altman analysis revealed mean differences between the 2 measurements ranging from −0.05 to 0.07 mm. The largest discrepancy in alveolar bone thickness was observed at CEJ-5 (mean difference = 0.07 mm; limits of agreement = −0.46 to 0.61 mm; Fig 5 ). The absolute mean differences were less than 0.15 mm at all sites, indicating good consistency. Alveolar bone thickness and vertical height data were normally distributed (Shapiro-Wilk test, P > 0.05).
Bland-Altman plots illustrating the measurement error in CBCT-measured alveolar bone thickness at the CEJ-5 level. Circle, difference between 2 measurements (y-axis) relative to their mean (x-axis); Dashes , mean difference (Diff); Lines , 95% limits of agreement.
Effect sizes were interpreted based on Cohen’s (1988) criteria as follows: trivial (d <0.2), small (0.2-0.5), moderate (0.5-0.8), and large (>0.8) following orthodontic CBCT meta-analyses. The independent t test exhibited no statistically significant variations in alveolar bone thickness between genders or between the left and right sides. From T0 to T1, statistically significant decreases were noted in most measured parameters ( Table II ). A significant decrease in labial alveolar bone thickness occurred at 2 mm apical to the CEJ (0.30 ± 0.24 mm, P <0.001; 95% CI, 0.24-0.36; d = 0.41). Similarly, at 5 mm apical to the CEJ on the labial side, the bone thickness demonstrated a statistically significant decrease (0.25 ± 0.27 mm, P = 0.001; 95% CI, 0.18-0.32; d = 0.33). On the lingual aspect, a significant reduction in alveolar bone thickness was noted at 7 mm apical to the CEJ (0.45 ± 0.82 mm, P = 0.021; 95% CI, 0.24-0.66; d = 0.46). Moreover, the apical lingual alveolar bone exhibited a pronounced decrease in thickness (1.22 ± 1.06 mm, P <0.001; 95% CI, 0.95-1.49; d = 0.51). Conversely, alveolar bone height increased on the labial and lingual sides. The labial inclination of the mandibular central incisors also increased significantly from T0 to T1.
Table II
Changes in height and thickness of the labial and lingual alveolar bone of mesial incisors in T0 and T1
| Measurement | T0 | T1 | T0 − T1 | P values |
|---|---|---|---|---|
| ABH-la | 1.93 ± 1.38 | 3.20 ± 2.36 | −1.26 ± 2.03 | 0.001 |
| ABH-li | 2.58 ± 1.29 | 4.73 ± 2.95 | −2.15 ± 2.88 | <0.001 |
| CEJ-2la | 1.00 ± 0.22 | 0.70 ± 0.14 | 0.30 ± 0.24 | <0.001 |
| CEJ-2li | 0.99 ± 0.26 | 0.77 ± 0.41 | 0.22 ± 0.38 | 0.227 |
| CEJ-2 | 6.33 ± 0.68 | 5.97 ± 0.75 | 0.36 ± 0.52 | <0.001 |
| CEJ-5la | 0.89 ± 0.41 | 0.64 ± 0.29 | 0.25 ± 0.27 | 0.001 |
| CEJ-5li | 1.21 ± 0.62 | 0.96 ± 0.40 | 0.25 ± 0.74 | 0.191 |
| CEJ-5 | 6.29 ± 0.84 | 5.93 ± 0.81 | 0.36 ± 0.84 | 0.021 |
| CEJ-7la | 0.71 ± 0.44 | 1.11 ± 0.50 | 0.41 ± 0.64 | 0.115 |
| CEJ-7li | 1.64 ± 0.91 | 1.20 ± 0.63 | 0.45 ± 0.82 | 0.021 |
| CEJ-7 | 5.98 ± 1.06 | 5.72 ± 0.98 | 0.26 ± 0.95 | 0.119 |
| CEJ-Ala | 2.12 ± 0.88 | 3.03 ± 1.64 | 0.91 ± 1.32 | 0.061 |
| CEJ-Ali | 3.79 ± 1.26 | 2.57 ± 1.01 | 1.22 ± 1.06 | <0.001 |
| CEJ-A | 6.07 ± 1.69 | 5.70 ± 1.82 | 0.37 ± 1.05 | 0.050 |
| IMPA | 79.63 ± 8.54 | 86.49 ± 7.41 | −6.86 ± 8.04 | <0.001 |
| L1-NB | 22.08 ± 7.07 | 29.68 ± 7.71 | −7.59 ± 8.06 | <0.001 |
Note. Values are presented as mean ± standard deviation.
ABH , distance between CEJ and crest of alveolar ridge; la , labial side; li , lingual side.
After presurgical orthodontic treatment, the incisal edge of the mandibular central incisors exhibited 3.87 mm labial movement, whereas the root apex exhibited nonsignificant movement. In addition, a nonstatistically significant labiolingual movement was observed at the alveolar crest. This lack of discernible movement may be linked to alveolar bone remodeling and a reduction in vertical bone height during the treatment ( Table III ).
Table III
Position of the mandibular central incisors at T0 and T1
| Measurement | T0 | T1 | T0 − T1 | P value |
|---|---|---|---|---|
| edge-VRP | 70.03 ± 4.96 | 74.01 ± 6.34 | −3.87 ± 1.79 | 0.041 |
| li-VRP | 63.90 ± 5.19 | 64.79 ± 6.46 | −0.91 ± 1.94 | 0.801 |
| la-VRP | 68.20 ± 5.05 | 67.77 ± 7.11 | 0.65 ± 2.34 | 0.445 |
| apex-VRP | 62.37 ± 5.82 | 63.42 ± 9.03 | 0.77 ± 1.33 | 0.172 |
Note. Values are’ presented as mean ± standard deviation.
edge-VRP , the distances from the VRP to the incisal edge; li-VRP , the distances from the VRP to the lingual alveolar crests; la-VRP , the distances from the VRP to the labial alveolar crests; edge-VRP , the distances from the VRP to the root apex.
The chi-square test results indicated no gender difference in the incidence of bone defects. At T0, fenestration and dehiscence were observed on the labial and lingual aspects of the mandibular central incisors ( Table IV ). After presurgical orthodontic treatment, a marked increase in the prevalence of alveolar bone defects was observed.
Table IV
Occurrence of fenestration and dehiscence
| Measurements | T0 (n = 60) | T1 (n = 60) | Total (n = 120) | ||||
|---|---|---|---|---|---|---|---|
| H | D-F/DF | H | D-F/DF | H | D-F/DF | P value (χ 2) | |
| 31la | 29 (48.3) | 31 (51.7) | 16 (26.7) | 44 (73.3) | 45 (37.5) | 75 (62.5) | 0.014 |
| 31li | 26 (43.3) | 34 (56.7) | 17 (28.3) | 43 (71.7) | 43 (35.8) | 77 (64.2) | 0.087 |
| 41la | 29 (48.3) | 31 (51.7) | 14 (23.3) | 46 (76.7) | 43 (35.8) | 77 (64.2) | 0.004 |
| 41li | 30 (50.0) | 30 (50.0) | 12 (20.0) | 48 (80.0) | 42 (35.0) | 78 (65.0) | <0.001 |
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