Abstract
Background
The surgical outcomes and stability of patients with skeletal Class II malocclusion determine the success of treatment. Variations in surgical interventions, patient responsiveness, and growth patterns across vertical facial morphologies result in varying treatment outcomes and postoperative stability.
Methods
This retrospective study recruited 52 adults diagnosed with skeletal Class II malocclusion treated with bimaxillary surgery; these adults were divided into two groups according to their vertical facial patterns. Cone-beam computed tomography images were collected before surgery (T0), after surgery (T1), and after orthodontic treatment (T2). Reconstructed three-dimensional images were used for cephalometric measurements and analysis.
Results
From T0 to T1, the Frankfort-mandibular plane angle decreased in the high-angle group but increased in the low–medium-angle group. The mandible advanced 9.02 and 6.21 mm in the high-angle and low–medium-angle groups, respectively. From T1 to T2, significant changes were observed in the anterior mandible horizontal movement of the high-angle group (−1.91 ± 3.63 mm) compared with the low–medium-angle group (−0.57 ± 1.04 mm). There were more patients exhibit clinically significant relapse (>2 mm) in the high-angle group (44 %) than in the low–medium-angle group (20 %).
Conclusion
The relapse patterns in the two groups were similarly upward and backward. However, the high angle group exhibited greater average postoperative changes. The proportion of patients who exhibited a clinically significant relapse was higher in the high angle group.
Keywords: Postoperative stability, Vertical facial pattern, Three-dimensional cephalometry, Skeletal Class II malocclusion, Orthognathic surgery
Highlights
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3D cephalometric analysis enabled precise evaluation of surgical changes.
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High-angle group showed higher relapse rates post-surgery; 10-15% overcorrection of planned distance is required.
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Low–medium-angle group demonstrated smaller mandibular advancement but superior stability across all dimensions.
1. Introduction
Surgical orthodontic treatment for patients with skeletal Class II malocclusion could alter and improve facial profile and airway patency in Class II deformities [[1], [2], [3]]. Patients with skeletal Class II malocclusion having varied vertical growth patterns require different treatment plans and exhibit different surgical responses [4,5]. For patients with a high mandibular plane angle, Maxillary impaction is indicated for reducing the vertical facial height [6,7]. By contrast, it might not be required for patients with a medium or low mandibular plane angle. These patients similarly require mandibular advancement to improve the position of the mandible [8]. Although some variations occur in the other movement. For high angle patient, mandible would have a counterclockwise rotation, hence reduce the mandibular plane angle. By contrast, in patients with a low or medium angle, mandible would have a clockwise rotation [9].
The advancement of the maxillo-mandibular complex can cause further soft tissue tension, which can lead to inferior relapse of the anterior mandible [10]. However, the current technique of rigid internal fixation can withstand more muscle tissue tension [7]. For skeletal Class II patients, Previous studies have demonstrated a close association between the presurgical mandibular plane angle and postsurgical stability or relapse [6,9]. Horizontal relapse occurs more frequently in patients with high mandibular plane angle, and vertical relapse occurs more frequently in patients with low mandibular plane angles [9,11]. Nevertheless, some studies have reported a contrasting finding, namely that the initial mandibular plane angle is not related to relapse [5,10]. Several studies found a positive correlation between an amount of mandibular advancement and a postoperative stability of mandible [[10], [11], [12]]. Therefore, controversy still exists regarding whether the presurgical vertical facial patterns is factor effecting the stability for patients with skeletal Class II.
Majority of earlier research have focused on the single jaw bilateral sagittal split osteotomies (BSSO) [9,13,14]. Furthermore, most of the previous studies were based on lateral cephalograms which represent only two dimensions from the radiograph to compare postoperative stability [4,6,9,14,15]. The use of three-dimensional (3D) cephalometric measurements enhances the quality of image evaluation for the position of the jaw bones.
The aim of this study was to compare the surgical outcomes and the postoperative stability in patients with skeletal Class II malocclusion having different vertical facial patterns by using a series of three-dimensional cone-beam computed tomography images after bimaxillary surgery treatment.
2. Materials and methods
2.1. Study design and patients
This retrospective study recruited Taiwanese patients who were diagnosed with skeletal Class II malocclusion and treated with bimaxillary orthognathic surgery at the Craniofacial Center of Chang Gung Memorial Hospital between 2013 and 2022. All the patients were operated on by the same team of surgeons and treated by single orthodontist. The inclusion criteria were: (1) age >20 years; (2) diagnosis of skeletal Class II malocclusion with no evident facial asymmetry (menton deviation of <4 mm); (3) no additional surgical procedures performed except for genioplasty; and (4) complete clinical and 3D imaging data. The exclusion criteria were: (1) previous facial surgery (e.g., cosmetic surgery); (2) congenital craniofacial anomalies (e.g., cleft lip and palate); and (3) major facial trauma history.
All surgeries were performed by the same team of surgeons and a single orthodontist. Presurgical preparation followed either a surgery-first or surgical-early approach. Osteotomies were guided by 3D surgical simulation and executed using 3D-printed surgical stents, including both intermediate and final occlusal stents.
In surgical occlusion setup, sagittal relationships were primarily determined by molar and canine positions, with a recommended degree of mild overcorrection. However, the incisor relationship—specifically overbite (OB) and overjet (OJ)—varied depending on factors such as incisor inclination, arch space, and crowding. In cases where postoperative retraction of the lower anterior teeth was not required, a shallow positive OB and OJ could be established. Conversely, when postoperative lower anterior retraction was anticipated, an edge-to-edge or even anterior crossbite setup was intentionally adopted. This strategy accounts for expected vertical changes during postoperative bite settling, such as slight upward movement of point B, while ensuring sufficient overbite to maintain occlusal stability.
The required sample size of 23 in each group was calculated using G∗Power 3 software (Dusseldorf, Germany), with p < 0.05 indicating statistical significance, power of 80 %, and an effect size of 0.80 for detecting differences in skeletal changes over time in each group [4].
This study was performed in accordance with the Declaration of Helsinki. The ethical approval for this study was provided by the Institutional Review Board and Medical Ethics Committee of Chang Gung Memorial Hospital (No. 202400689B0).
2.2. Data collection and measurement
A series of cone-beam computed tomography (CBCT) images were captured at three time points: T0, before surgery; T1, after surgery; and T2, upon completion of orthodontic treatment. The CBCT images were obtained using an i-CAT system (DEXIS, Pennsylvania, USA; 120 kVp and 36.9 mAs, FOV: 22 cm [height] × 16 cm [depth], scanning time: 40 s, voxel size: 0.4 × 0.4 × 0.4 mm3). All scans were taken in the natural head position with centric occlusion. CBCT images were then imported into PROPLAN CMF™ software (Materialise Dental, Leuven, Belgium) to reconstruct 3D images. Landmarks used for 3D analysis included: S (sella turcica), N (nasion), B (B point), A (A point), Po(R) (right porion), Co(R) (right condylion), Co(L) (left condylion), Or(R) (right orbitale), Or(L) (left orbitale), U1 (upper incisor), L1 (lower incisor), Pog (pogonion), Me (menton), Go(R) (right gonion), and Go(L) (left gonion). These landmarks were identified in the reconstructed images at all three time points. Reference planes for 3D reconstructed images positioning were the mid-sagittal plane (MSP), coronal plane (CP), and Frankfort horizontal plane (FHP). In the sagittal direction, anterior to the coronal plane was defined as a positive value. In the vertical direction, inferior to the Frankfort horizontal plane was defined as a positive value. Superimposition of the three images for each patient was performed using registration at the frontonasal area and anterior cranial base. Consistency in this process was ensured through a surface-based method.
2.3. Study variables
The vertical facial type, classified according to the Frankfort-mandibular plane angle (FMA), was the primary predictor variable. The reference values used for the FMA were based on the Asian 3D cephalometric norms [16,17]. The analyzed patients were classified into high-angle (FMA >32°), medium-angle (FMA = 22°–32°), and low-angle (FMA <22°) groups. However, owing to an insufficient number of low-angle patients, the study population was instead divided into two groups, namely high-angle (HA; FMA >32°) and low–medium-angle (LMA; FMA 32°) groups.
Regarding the primary outcome variable, linear and angular measurements were performed using the craniofacial landmarks [Fig. 1]. The changes of each measurement from T0 to T1 were defined as surgical changes. The difference of each measurement from T1 to T2 were defined as postoperative changes. According to the definition by Proffit et al., the secondary outcomes variables involve the percentage of patients that exhibited clinically significant changes of more than 2 mm [3].
Fig. 1.
3D reconstructed model showing craniofacial measurements. (A) Angular measurement: SNA is the angle between sella (S), nasion (N), and point A. SNB is the angle between sella, nasion, and point B. ANB is the angle between point A, nasion, and point B. FMA is the angle between the Frankfort horizontal plane (FHP) and the mandibular plane (MP). (B)Linear measurement: A-CP, B-CP, Pog-CP, and Me-CP indicate the distances from point A, point B, pogonion, and menton to the coronal plane (CP). A-FHP, B-FHP, Pog-FHP, and Me-FHP indicate the distances from the same landmarks to the Frankfort horizontal plane. (C) Transverse measurement: The intercondylar distance is measured between the right and left condylion points (Co(R)–Co(L)). The intergonial distance is measured between the right and left gonion points (Go(R)–Go(L)). Ramus height is defined as the vertical distance from the condyle to gonion on both sides.
2.4. Statistical analysis
Statistical analyses were performed using SPSS Statistics version 29.0 for Mac (IBM, Chicago, IL, USA). Pearson's chi-square test was used to compare age, sex, and maxillary and mandibular surgical approaches between the groups. The Shapiro–Wilk test was conducted to assess normality of all measured variables. Based on the results, between-group comparisons were performed using either the independent samples t-test for normally distributed data or the Mann–Whitney U test for non-normally distributed data. Within-group comparisons (pre- and post-surgery) were analyzed using the paired t-test for normally distributed data and the Wilcoxon signed-rank test for non-normally distributed data. The proportions of patients in each group with clinically significant relapse were compared using Pearson's chi-square test. Intra-rater reliability was assessed by second landmarking and measuring 15 randomly selected samples after 4 weeks interval and intraclass correlation were test on all variables. Statistical significance was set at p < 0.05.
3. Results
The intraclass correlation coefficient ranged from 0.851 to 0.999 for all identified landmarks and measured variables, indicating high intra-rater reliability.
This study analyzed 27 patients in the HA group and 25 patients in the LMA group. The follow-up periods were 24.21 ± 8.66 months for the HA group and 19.16 ± 9.00 months for the LMA group. Statistically significant differences of follow-up duration were observed between the groups. The distribution of mandibular and maxillary surgical approaches was comparable between the two groups [Table 1]. Postoperative stabilities were compared among different maxillary surgical approaches, and the postoperative changes at point A were found to be non-significant (A-CP, p = 0.141; A-FHP, p = 0.345).
Table 1.
Patients’ demographic data.
| HA | LMA | P-value | |
|---|---|---|---|
| No. of patient | 27 | 25 | |
| Sex | 0.100a | ||
| Female | 19 (70.4 %) | 12 (48 %) | |
| Male | 8 (29.6 %) | 13 (52 %) | |
| Age (Year) | 25.29 ± 5.72 | 29.30 ± 10.04 | 0.080b |
| Preoperative treatment duration (month) | 8.57 ± 7.47 | 9.47 ± 9.76 | 0.715c |
| Postoperative treatment duration (month) | 24.21 ± 8.66 | 19.16 ± 9.0 | 0.021∗ c |
| Maxillary surgery | 0.436a | ||
| LeFort 1 | 14 (51.9 %) | 16 (64 %) | |
| 2-Pieces segmental | 6 (22.2 %) | 6 (24 %) | |
| 3-Pieces segmental | 7 (25.9 %) | 3 (12 %) | |
| Mandibular surgery | 0.623a | ||
| BSSO | 1 (3.7 %) | 0 (0 %) | |
| BSSO + G | 25 (92.6 %) | 24 (96 %) | |
| BSSO + G + K | 1 (3.6 %) | 1 (4 %) |
Abbreviations:FMA: angle formed between the Frankfort horizontal plane and the mandibular plane; SD: standard deviation; HA: high-angle; LMA: low–medium-angle; BSSO: bilateral split sagittal osteotomy; G: genioplasty; K: Köle osteotomy.
∗p < 0.05.
Chi-squared test.
Independent samples t-test.
Mann–Whitney U test.
3.1. Patient characteristics before surgery
Significant differences were observed in the mean FMAs between the HA and LMA groups (40.11° ± 5.89° and 27.28° ± 3.14°, respectively). Presurgical sagittal linear measurements, angular measurements, condylar width, and ramus height exhibited significant intergroup differences. The mean A-CP distances were 84.24 ± 6.54 and 89.26 ± 4.90 mm; p < 0.05, for the HA and LMA groups, respectively. The mean B-CP distances were 69.12 ± 9.50 and 79.49 ± 5.30 mm; p < 0.001, for the HA and LMA groups, respectively. However, no significant differences were observed in vertical linear measurements, except for B-FHP [Table 2].
Table 2.
Patients’ presurgical characteristics (T0).
| HA |
LMA |
P-value | |||
|---|---|---|---|---|---|
| mean | SD | mean | SD | ||
| Angular measurement | |||||
| FMA | 40.11 | 5.89 | 27.28 | 3.14 | <0.001b∗∗ |
| ANB | 8.39 | 2.87 | 6.58 | 2.08 | 0.013a∗ |
| SNA | 82.46 | 3.63 | 85.29 | 3.23 | 0.005a∗ |
| SNB | 74.14 | 3.95 | 78.88 | 3.21 | <0.001a∗∗ |
| Sagittal measurement | |||||
| N-CP | 84.30 | 6.19 | 87.48 | 5.61 | 0.034a∗ |
| A-CP | 84.24 | 6.54 | 89.26 | 4.90 | 0.003b∗ |
| B-CP | 69.12 | 9.50 | 79.49 | 5.30 | <0.001a∗∗ |
| Pog-CP | 67.53 | 11.26 | 79.21 | 5.21 | <0.001a∗∗ |
| Me-CP | 60.85 | 12.01 | 72.59 | 5.03 | <0.001a∗∗ |
| Vertical measurement | |||||
| N-FHP | 27.52 | 2.66 | 27.07 | 2.60 | 0.568a |
| A-FHP | 33.01 | 3.43 | 30.86 | 3.28 | 0.025b∗ |
| B-FHP | 74.98 | 4.46 | 71.66 | 5.10 | 0.016a∗ |
| Pog-FHP | 85.46 | 6.90 | 83.68 | 5.07 | 0.300a |
| Me-FHP | 91.57 | 8.83 | 90.61 | 5.16 | 0.639a |
| Transverse measurement | |||||
| Intergonion distance | 94.50 | 6.34 | 94.75 | 6.38 | 0.885a |
| Intercondylar distance | 110.26 | 5.08 | 113.91 | 7.40 | 0.042a∗ |
| Ramus measurement | |||||
| Ramus height (R) | 50.38 | 5.57 | 56.57 | 4.98 | <0.001a∗∗ |
| Ramus height (L) | 49.56 | 4.65 | 56.21 | 5.58 | <0.001a∗∗ |
| Dental measurement | |||||
| U1-SN | 98.74 | 7.98 | 100.56 | 6.57 | 0.589b |
| L1-MP | 92.69 | 8.47 | 95.76 | 9.05 | 0.212a |
HA, high-angle; LMA, low–medium-angle; T0, before surgery.
∗p < 0.05.
∗∗p < 0.01.
Independent samples t-test.
Mann–Whitney U test.
3.2. Surgical outcomes
The FMA of the HA group significantly decreased through surgery, with a change of 5.28° ± 3.13° (p < 0.001). By contrast, the FMA of the LMA group exhibited only a minimal increase after surgery, namely 0.01° ± 2.71°. Statistically significant differences were observed between the groups, except for the SNA, A-CP, and A-FHP [Table 3].
Table 3.
Comparison of surgical changes (T1-T0) between the 2 groups.
| HA |
P-value | LMA |
P-value | P-value | |||
|---|---|---|---|---|---|---|---|
| mean | SD | mean | SD | ||||
| Angular measurement | |||||||
| FMA | −5.28 | 3.13 | <0.001c∗∗ | 0.01 | 2.71 | 0.981c | <0.001a∗∗ |
| ANB | −3.85 | 2.02 | <0.001d∗∗ | −3.01 | 2.34 | <0.001c∗∗ | 0.060b |
| SNA | 0.47 | 3.06 | 0.434c | 0.24 | 4.07 | 0.767c | 0.823a |
| SNB | 4.90 | 3.01 | <0.001c∗∗ | 3.52 | 2.95 | <0.001c∗∗ | 0.102a |
| Sagittal measurement | |||||||
| A-CP | 0.47 | 3.11 | 0.438c | 0.40 | 4.29 | 0.904d | 0.436b |
| B-CP | 9.02 | 5.54 | <0.001c∗∗ | 6.21 | 5.35 | <0.001c∗∗ | 0.070a |
| Pog-CP | 13.80 | 7.99 | <0.001c∗∗ | 9.99 | 6.68 | <0.001c∗∗ | 0.068a |
| Me-CP | 14.35 | 9.17 | <0.001d∗∗ | 10.93 | 7.02 | <0.001c∗∗ | 0.071b |
| Vertical measurement | |||||||
| A-FHP | −1.79 | 2.32 | <0.001c∗∗ | −0.94 | 1.96 | 0.024c∗ | 0.163a |
| B-FHP | −1.76 | 2.62 | 0.002c∗ | 1.60 | 2.88 | 0.010c∗ | <0.001a∗∗ |
| Pog-FHP | 2.62 | 4.80 | 0.002d∗ | 3.20 | 3.02 | <0.001c∗∗ | 0.111b |
| Me-FHP | 2.32 | 7.50 | 0.073d | 2.86 | 3.00 | <0.001c∗∗ | 0.058b |
| Transverse measurement | |||||||
| Intergonion distance | 1.61 | 4.62 | 0.81c | 4.04 | 2.86 | <0.001c∗∗ | 0.051a |
| Intercondylar distance | 2.03 | 4.02 | 0.014c | 1.64 | 3.08 | 0.014c∗ | 0.693a |
| Ramus measurement | |||||||
| Ramus height (R) | −0.52 | 2.05 | 0.201c | −1.75 | 2.36 | <0.001c∗∗ | 0.052a |
| Ramus height (L) | −0.56 | 1.80 | 0.156d | −1.91 | 3.09 | <0.001d∗ | 0.101b |
| Dental measurement | |||||||
| U1-SN | −4.41 | 8.63 | 0.066c | −5.41 | 11.11 | 0.656c | 0.848b |
| L1-MP | 8.68 | 9.23 | 0.486d | 5.66 | 10.61 | 0.840d | 0.117b |
∗p < 0.05.
∗∗p < 0.01.
Independent samples t-test.
Mann–Whitney U test.
Paired t-test.
Wilcoxon signed-ranked test.
Regarding sagittal movement, the A point moved forward less than 0.5 mm in both groups. By contrast, the B point moved forward significantly, with a mean advancement of 9.02 ± 5.54 and 6.21 ± 5.35 mm in the HA and LMA groups, respectively [Table 3].
Both the HA and LMA groups exhibited superior movement of the A point (1.79 ± 2.32 and 0.94 ± 1.96 mm, respectively). However, the movement of the B point differed; in the HA group, the B point moved upward by 1.76 ± 2.62 mm, whereas in the LMA group, the B point moved downward by 1.60 ± 2.88 mm (p < 0.001). All changes in vertical linear measurements were nonsignificant between the two groups, except for that for B-FHP [Table 3].
The movement direction of the A point from T0 to T1 were upward and forward in both groups. However, the amount of vertical movement in HA was larger. The movement direction of the B point was forward and upward in the HA group but forward and downward in the LMA group [Fig. 2].
Fig. 2.
Average change in maxillary and mandibular position (A point and B point). Average horizontal and vertical changes in the A point (left) and B point (right) from T0 to T1 and to T2. A point and B point are normalized to 0 at T0. In the sagittal direction, a positive value indicates forward movement. In the vertical direction, a positive value indicates downward movement.
3.3. Postoperative stability
From T1 to T2, The FMA of the HA group significantly increase 2.59° ± 2.70° (p< 0.001). By contrast, the LMA group exhibited only a minimal increase of 0.31° ± 1.58°.
Regarding maxillary stability, the A-CP distance also significantly decreased from T1 to T2, namely −1.05 ± 1.00 mm and −0.74 ± 1.04 in the HA and LMA groups, respectively. The A-FHP distance of the two groups showed slight increases with less than 0.5 mm changes. [Table 4].
Table 4.
Comparison of Postoperative changes (T2-T1) between the 2 groups.
| HA |
P-valueb | LMA |
P-valueb | P-value | |||
|---|---|---|---|---|---|---|---|
| mean | SD | mean | SD | ||||
| Angular measurement | |||||||
| FMA | 2.59 | 2.70 | <0.001c∗∗ | 0.31 | 1.58 | 0.236d | 0.002b∗ |
| ANB | 0.26 | 1.72 | 0.446c | −0.41 | 1.32 | 0.131c | 0.120a |
| SNA | −1.02 | 0.99 | <0.001d∗∗ | −0.78 | 1.00 | 0.001c∗ | 0.826b |
| SNB | −1.08 | 2.01 | 0.010c | −0.33 | 1.13 | 0.158c | 0.108a |
| Sagittal measurement | |||||||
| A-CP | −1.05 | 1.00 | <0.001d∗ | −0.74 | 1.04 | 0.002c∗ | 0.714b |
| B-CP | −1.91 | 3.63 | 0.011c∗ | −0.57 | 1.97 | 0.164c | 0.108a |
| Pog-CP | −3.40 | 3.87 | <0.001c∗ | −0.86 | 2.01 | 0.009d∗ | 0.032b∗ |
| Me-CP | −3.56 | 4.31 | <0.001c∗ | −0.94 | 2.16 | 0.040c∗ | 0.009a∗ |
| Vertical measurement | |||||||
| A-FHP | 0.46 | 1.27 | 0.146d | 0.49 | 1.01 | 0.037d∗ | 0.833b |
| B-FHP | −1.04 | 3.91 | 0.110d | −0.66 | 2.21 | 0.150c | 0.847b |
| Pog-FHP | −0.15 | 1.89 | 0.677c | −0.53 | 2.17 | 0.237c | 0.511a |
| Me-FHP | 0.35 | 1.54 | 0.248c | −0.58 | 1.77 | 0.178d | 0.047b∗ |
| Transverse measurement | |||||||
| Intergonion distance | −1.25 | 2.39 | 0.011d∗ | −1.35 | 1.79 | <0.001c ∗∗ | 0.589b |
| Intercondylar distance | −1.43 | 4.28 | 0.121d | −1.47 | 2.79 | 0.006c∗ | 0.431b |
| Ramus measurement | |||||||
| Ramus height (R) | −1.19 | 2.51 | 0.021c∗ | −0.32 | 1.36 | 0.251c | 0.133a |
| Ramus height (L) | −0.67 | 2.61 | 0.196c | 0.27 | 1.77 | 0.778d | 0.301b |
| Dental measurement | |||||||
| U1-SN | 3.36 | 9.02 | 0.051c∗ | 1.80 | 22.78 | 0.783c | 0.743a |
| L1-MP | −14.50 | 12.76 | <0.001c∗∗ | −16.06 | 20.41 | 0.004c∗ | 0.750a |
∗p < 0.05.
∗∗p < 0.01.
Independent samples t-test.
Mann–Whitney U test.
Paired t-test
Wilcoxon signed-ranked test.
Regarding mandibular stability, the B-CP distance decreased by −1.91 ± 3.63 mm and −0.57 ± 1.97 mm in the HA and LMA groups, respectively. In the HA group, significant changes were detected only in B-CP from T1 to T2. The postsurgical position changes in Pog-CP and Me-CP were significantly different between the HA and LMA groups. Regarding changes in vertical linear measurements, the HA and LMA groups exhibited decreases in B-FHP of −1.04 ± 3.91 and −0.66 ± 2.21 mm, respectively [Table 4]. In both groups, mandibular position changes in the B point from T1 to T2 occurred in a similar direction, yielding a backward and upward relapse pattern [Fig. 2].
In the assessment of the percentage of patients having relapse of the A point [Fig. 3], it was observed that both groups experienced substantial posterior movement. For clinically significant changes, 14.81 % and 8 % of the patients in the HA and LMA groups, respectively, exhibited >2-mm backward movement. Regarding the postoperative vertical changes of the A point, 7.41 % and 8 % of the patients in the HA and LMA groups, respectively, exhibited movement of >2 mm. The chi-square test showed no significant difference between the HA and LMA groups for proportions of patient having clinically significant relapse at point A in both A-CP (χ2 = 0.670, df = 1, p = 0.413) and A-FHP (χ2 = 0.002, df = 1, p = 0.967).
Fig. 3.
Percentage of patients exhibit horizontal (left) and vertical (right) relapse of the A point after surgery (T2–T1). ∗ Indicates clinically significant relapse (>2 mm).
In the assessment of the percentage of patients having relapse of the B point [Fig. 4], high proportions of patients in both groups exhibited backward movement. Moreover, 44 % and 20 % of the patients in the HA and LMA groups, respectively, exhibited >2-mm backward movement. The chi-square test showed a significant difference in patients having clinically significant higher relapse (>2 mm) proportion between the HA and LMA groups regarding the B-CP (χ2 = 3.923, df = 1, p = 0.0476). Regarding the postoperative vertical changes of B point, 7.41 % of the patients in the HA group and 8 % of the patients in LMA group exhibited movement of >2 mm. No significant difference was found for B-FHP between the two groups (χ2 = 0.002, df = 1, p = 0.967).
Fig. 4.
Percentage of patients exhibit horizontal (left) and vertical (right) relapse of the B point after surgery (T2–T1). ∗ Indicates clinically significant relapse (>2 mm).
4. Discussion
Variations in surgical plan and growth patterns across vertical facial morphologies result in varying postoperative stability [2,3]. In this study, Despite the difference in surgical movement between the two groups, their average relapse directions were similar. Regarding the characteristics of the patients before surgery [Table 2], the HA group exhibited distinct characteristics relative to the LMA group. Before surgery, maxillary protrusion was more evident in the HA group, but mandibular retrusion was more evident in the LMA group. These findings contrast with those of Marangoni et al., who reported no significant difference in the SNA and SNB angles between the two groups [4]. The distance between coronal plane and A point, B point, and Pogonion were significantly larger in the HA group. In addition, the anterior facial height in the HA group was greater than that in the LMA group. This facial characteristic of both groups reflects the dolichofacial and brachyfacial growth patterns, as mentioned in previous studies [[18], [19], [20]]. Mizugochi et al. explained that the HA patients exhibit downward–backward rotation of the mandible resulting form postero-superior growth of the condyle together with bone apposition in the inferior border of the mandible, giving the impression of a longer vertical dimension [21]. The hypodivergent type is characterized by an elongated horizontal component. Correspondingly, in individuals with a short-faced type, excessive forward growth rotation of the mandible occurs, leading to a shorter anterior lower face height [18,19,22].
Treatment plans and surgical movement vary in accordance with the characteristics observed in different facial growth patterns [Table 3]. From T0 to T1 [Fig. 2], the surgical movement direction of the maxilla was upward and forward in both groups, although the change was nonsignificant. However, in the mandible, the B point moved upward 1.76 mm, and the Gonion moved upward 0.54 mm in the HA group. This finding indicated the differential superior movement of the B point and gonion and was consistent with previous findings showing that such movement resulted in decreases in the FMA and the anterior facial height [6,9]. By contrast, in LMA group, the B point moved downward 1.60 mm while the Gonion moved upward 1.83 mm. This result indicated the clockwise rotation of the mandible. In both groups, downward movement of the gonion was carefully avoided to maintain muscle stability, contributing to the preservation of the condyle. The amount of advancement of the mandible was significantly larger in the HA group. These amount of advancement in both group were larger than those reported in previous studies [9,13,14,23]. Furthermore, a significant discrepancy in the advancement between A point and B point was observed across both groups. This difference could be attributed to the segmental osteotomies in the maxilla, which were intended to facilitate a minimal repositioning of maxilla with large amount of advancement of mandible. As well as in single piece LeFort I surgery, rotational movement of the maxillo-mandibula complex were necessary to accommodate the differential advancements of the two jaws.
In the present study [Table 4], postoperative changes at points A and B in both the vertical and horizontal directions were not statistically significant between the HA and the LMA groups. However, the Pogonion demonstrated a significant difference between the two groups in the horizontal direction, while Menton showed significant differences in both horizontal and vertical dimensions. These findings may be attributed to the effects of genioplasty remodeling. LeFort 1 osteotomy provided a relatively stable result, with average relapse of 1.05 mm horizontally and 0.5 mm vertically. These results are consistent with those of previous results indicating that maxillary osteotomy is highly stable [3]. The relapse patterns appeared to be downward and backward in both groups [Fig. 2]. The mandibular relapse in the present study was comparable to that reported by Eggensperger et al., who similarly indicated slightly larger horizontal relapse in their HA group [13]. However, our results revealed larger average horizontal relapse when measured at the pogonion (3.4 mm in the HA group) partly from the remodeling of genioplasty [10]. Regarding the vertical dimension, in both groups, the B point moved upward, although superior surgical movement was found in the HA group [Fig. 2]. This reduction of the anterior facial height resulted from bite settling and the finishing phase in the postsurgical orthodontic treatment [24]. In the present study, the proportion of patients with clinically significant relapse (>2 mm) was significantly higher (p = 0.0476) in the HA group (44 %) than in the LMA group (20 %) [Fig. 4]. This suggests that patients with a high mandibular plane angle may be more prone to horizontal relapse at B point following surgery. Which was consistent with those reported by Mobarak et al. The clinically significant relapse in both groups in the present study was lower than that reported by Mobarak et al. (55 % in the HA group, 30 % in the LA group) and Carvalho et al. (48 % in the combined group) [9,25]. This finding contrasting with the previous study, which observed that patients with a high angle exhibited less horizontal relapse than the other group [12]. In the present study, the proportions of patients in the HA (8 %) and LMA (7.41 %) groups who exhibited clinically significant vertical relapse at both the A and B points were almost identical. Following surgery, 29.61 % of the HA group and 36 % of the LMA group showed additional anterior movement of the B point, reflecting positive postoperative outcomes in both groups. In terms of vertical changes, up to 60 % of the HA group experienced an upward shift of the B point, which contributed to favorable treatment results. Conversely, only 30 % of the LMA group displayed the beneficial downward movement of the B point between T1 and T2 [Fig. 3, Fig. 4]. In the present study, the HA group exhibited less stability than did the LMA group, as indicated by the proportions of patients who had clinically significant relapse and average postoperative changes. According to the literature, the counterclockwise positional changes of condyle after surgery cause a compression force between glenoid fossa and condyle [26]. Additionally, patients with a hyperdivergent profile have a smaller condyle with less dense trabecular bone. This anatomical limitation may be the reason for the inferior ability of the condyle to adapt to increased muscle load [13,14,23]. A significant correlation was found between the degree of advancement at the B point and horizontal relapse (p < 0.05) in this study. Multiple studies have described that the degree of advancement from BSSO is significantly correlated with postsurgical relapse [12,14,27]. However, some studies have stated that the degree of surgical movement does not affect postoperative stability [5,13,28].
In the present study, in the HA group, the mean FMA decreased from 40.11° to 34.83° after surgery and then increased to 37.42° at T2 [Table 3]. This finding contrasts with that of Ruslin et al., namely that the preoperative FMA did not differ from the 1-year postoperative value [12]. However, the FMA of the LMA group exhibited minimal changes over time. These changes reflect the minimal surgical changes that occurred and also the higher stability in the LMA group relative to the HA group [6,9,13]. However, the intergonial distance changes after surgery may have resulted from the osteotomy through the gonion, leading to bone remodeling and positional changes of gonion. The decreased intercondylar distance after surgery marked the inward remodeling of the condylar head. L1-MP significantly decreased from T1 to T2 in both groups. The retroclination of the lower anterior teeth result from changes in the mandibular plane and decompensation tooth movement for achieving a dental Class I relationship [Table 4]. The HA group had a significantly longer postoperative treatment duration (T1–T2) than the LMA group, indicating a more complex treatment process. Moreover, orthodontic treatment process had to be adapted to the simultaneous relapse occurring throughout the process.
Until recently, few studies had examined stability across different vertical facial patterns. Accordingly, the present study compared stability after bimaxillary surgery in patients with skeletal Class II malocclusion across vertical facial types by utilizing 3D CBCT images. Nevertheless, this study had some limitations, namely its retrospective design, age and sex distributions, and comparatively short observation period. Thus, further investigation is warranted to assess condylar remodeling and soft tissue changes and for the long-term study of bimaxillary surgery.
5. Conclusion
Despite variations in surgical movement between the HA and LMA groups, the relapse patterns of the maxilla and mandible remained similar. The HA group experienced greater relapse, particularly in terms of clinically significant relapse and average postoperative changes in the vertical and sagittal dimensions. In contrast, the LMA group demonstrated greater stability across all dimensions. These findings highlight that surgical planning, outcomes, and relapse patterns in bimaxillary orthognathic surgery can vary significantly based on vertical facial type. Given the higher likelihood of relapse in the HA group, especially in horizontal direction, overcorrection of mandibular advancement by 10–15 % of the planned advancement distance may be advisable to accommodate potential backward and upward relapse.
Patient consent
Not required.
Author statement
Dr. Ellen Wen-Ching: Conceptualization, Methodology, Validation, Supervision. Wasuthorn Poolsin: Methodology, Formal analysis, Data Curation, Writing-Original Draft. Carol Yi-Hsuan Chen: Investigation, Resources. Cheng-Hui Lin, Investigation, Resources.
Ethical approval
This study was approved by the Institutional Review Board of Chang Gung Memorial Hospital (No.202400689B0).
Declaration of generative AI and AI-assisted technologies in the writing process
During the preparation of this work the authors did not use generative artificial intelligence (AI) and AI-assisted technologies for data management.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of interest
The authors declare no conflicts of interest.
Acknowledgments
We thank the Craniofacial Research Center in Chang Gung Memorial Hospital for the technical support in the 3D data analysis.
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