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Improved lip esthetics in patients with skeletal Class III malocclusion and facial asymmetry after isolated mandibular orthognathic surgery

Improved lip esthetics in patients with skeletal Class III malocclusion and facial asymmetry after isolated mandibular orthognathic surgery



American Journal of Orthodontics and Dentofacial Orthopedics, 2022-05-01, Volume 161, Issue 5, Pages e407-e415, Copyright © 2021 American Association of Orthodontists


Introduction

Asymmetry of the lips severely affects facial esthetics and is often one of the chief complaints of orthognathic patients, especially those with Class III malocclusion. The objectives of this study were to investigate the changes in lip symmetry in patients with mandibular prognathism and deviation and the relationships between jaw hard tissue and lip soft-tissue changes.

Methods

Three-dimensional facial scan and cone-beam computed tomography scan data of 30 orthodontic-orthognathic patients treated with bilateral sagittal split ramus osteotomy were combined to conduct the research. Paired-sample t test and Pearson correlation coefficient were applied to compare the differences in the same variable before and after the orthognathic surgery and the potential correlations between the changes in hard and soft variables. To explore the important hard tissue variables influencing the lip soft-tissue changes, linear regression analysis was performed.

Results

Although there was significant upper lip asymmetry presurgery, the upper lip asymmetry was corrected postsurgery. Surgical correction of the mandibular deviation was also accompanied by lengthening of the bilateral philtrum crests. Improvement in lip asymmetry and lengthening of the philtrum crests were primarily related to the transverse correction of the mandible rather than sagittal changes. The corresponding prediction formulas were established.

Conclusions

The isolated mandibular bilateral sagittal split ramus osteotomy surgery can substantially improve the upper and lower lip asymmetry in patients with mandibular prognathism and deviation, but one should be wary of the unesthetic effects associated with lengthening of the philtrum crests.

Highlights

  • Asymmetry of the lips presents in patients with mandibular prognathism and deviation.

  • Asymmetry of the lips can be corrected by BSSRO surgery.

  • Improvement in lip asymmetry was related to transverse correction of the mandible.

  • Correction of mandibular deviation was accompanied by lengthening of philtrum crests.

Symmetry and harmony of the lips are important factors in determining the esthetics of the lower part of the face. Asymmetry of the lips severely affects facial esthetics. It is often one of the chief complaints of the patients. Previous studies of lip symmetry have mainly focused on patients with cleft lip or palate. With increasing emphasis on facial beauty, improvement of lip esthetics has also been pursued by orthognathic patients. Therefore, orthognathic surgery should not be limited to improving the sagittal jaw relationship and profile protrusion of the patients. The correction results of lip asymmetry also directly affect the satisfaction of patients with orthognathic surgery.

For correction of asymmetric deformities, orthognathic surgery is usually performed. , Aoyama et al reported that lip asymmetry in patients with Class I relationships could be corrected by bimaxillary surgery by surgically flattening the occlusal plane and aligning the mandibular midline to the face. However, for patients with Class III malocclusion, the orthognathic surgery usually involved transverse correction and sagittal backward of the mandible, and even vertical movements, so which factor is related to the improvement of lip symmetry or which factor related more? No responses have yet been given from previous studies. Jeon et al insisted that the bilateral sagittal split ramus osteotomy (BSSRO) alone can greatly improve lip symmetry in patients with Class III malocclusion and facial asymmetry, but their predictor variables were mainly the lip line, which only involved improvement of lip symmetry in the transverse direction. The symmetry of the lip contains many other structures, such as the Cupid’s bow, the vermilion border, the angle of the mouth on both sides, which deserve further study. In addition, in other papers, some scholars , found no significant changes in upper lip length in patients with symmetrical mandibular prognathism treated with BSSRO procedure alone; the increase in upper lip length was mainly because of the anterior migration of the maxilla. So, whether patients with mandibular prognathism and deviation also have upper lip asymmetry, or whether isolated mandibular surgery will cause changes in the upper lip region in such patients? The answer is still unknown.

Therefore, the purpose of this study was to investigate the changes in lip symmetry in patients with mandibular prognathism and deviation after isolated mandibular BSSRO surgery; meanwhile, to further explore the relationship between surgical changes in lip and mandible; and finally, to make surgeons have a clearer understanding of facial soft-tissue changes and related bony factors after orthognathic surgery.

Material and methods

To investigate the changes in lip symmetry induced by isolated mandibular surgery, we designed this longitudinal study, which included 30 patients with mandibular protrusion and deviation and treated with BSSRO surgery by the same experienced surgeon from June 2019 to June 2021. Ethical approval of this study was granted by the Ethics Committee of Stomatological Hospital of Chongqing Medical University, and agreement to participate in the study was obtained from each patient. The following inclusion criteria were used to collect samples: (1) mandibular prognathism (SNB >84° and ANB <0°), (2) mandible deviation without severe occlusal plane deviation (the midpoint of the alveolar margin of the mandibular central incisors deviated from facial midline >2 mm), (3) orthognathic-orthodontic sequential treatment, (4) rigid fixation method, (5) complete hard and soft-tissue data before and 6 months after orthognathic surgery, and (6) body mass index range 18.5-23.9 kg/m 2 . The exclusion criteria were as follows: (1) 2-jaw surgery, LeFort I osteotomy was involved, (2) facial trauma or congenital deformity, (3) cleft lip and/or cleft palate, (4) surgery-first orthognathic approach, and (5) patients had genioplasty.

This study combined a 3-dimensional (3D) facial scanner Morpheus 3D (Morpheus, Gyoung-gi, Korea), and cone-bean computed tomography (CBCT) scanner (KaVo Dental GmbH, Bismarckring, Germany) to explore the hard and soft-tissue changes. Each patient underwent those 2 kinds of scans a week before the surgery and 6 months after the surgery. For 2 image acquisitions, all subjects were asked to keep their heads in a natural position to make the Frankfort Horizontal plane perpendicular to the floor and bite their teeth at the maximum intercuspation to reduce errors in the late fusion of the 2 images. The 3D facial scan data were saved in MPA (moving picture expert group associated files) format and CBCT data in DICOM (digital imaging and communications in medicine) format, then 2 data were stored in a specialized computer (Windows 10 operation system, Microsoft, Wash) for use.

The 3D facial scan data and CBCT data of the 2 stages were opened with MDS software (Morpheus, Gyoung-gi, Korea) for measurement and analysis. First, hard tissue models were reconstructed using the most suitable Hounsfield unit values, and 3D images of the facial soft tissue were adjusted for optimal visual recognition ( Fig 1 ). Then, superimposing the preoperative and postoperative soft-tissue models by a method of landmark-based superimposition (The superimposition result was presented as a color map) so that 2 models from the same patient would be unified into 1 coordinate system, as is shown in Figure 2 .

Soft and hard tissue models were used in this study: A, preoperative; B, postoperative.
Fig 1
Soft and hard tissue models were used in this study: A, preoperative; B, postoperative.

Superimposition of preoperative and postoperative facial models: A, preoperative model; B, postoperative model; C, superimposed model (color map).
Fig 2
Superimposition of preoperative and postoperative facial models: A, preoperative model; B, postoperative model; C, superimposed model (color map).

All measurements were performed on 3D models in MDS software. The side to which the chin deviated was defined as the deviated side (D), and the contralateral side as the nondeviated side (ND). For bony measurements, changes of the mandible in 3D space were represented with the 3D movements of the midpoint of the alveolar margin of the mandibular central incisors (Mid), rather than the Menton (Me) point used by previous studies, which had relatively lower accuracy for landmark location in 3D models. After that, the preoperative and postoperative 3D bony models were superimposed by a method of voxel-based superimposition to obtain the changes of bony landmarks. The mandibular hard tissue landmarks and measurement variables were detailed in Figure 3 and Table Ι .

Superimposition of preoperative and postoperative bony models: A, preoperative model; B, postoperative model; C, superimposed model.
Fig 3
Superimposition of preoperative and postoperative bony models: A, preoperative model; B, postoperative model; C, superimposed model.

Table I
Definition of hard and soft-tissue landmarks
Landmarks Definition
Mid Midpoint of the alveolar margin of the mandibular central incisors
Sbal (D/ND) The turning point of philtrum crest and nasal columella (deviated side/nondeviated side)
Cph (D/ND) The highest point of the arch of the upper lip (deviated side/nondeviated side)
Ch (D/ND) The outermost point of the joint of the upper and lower lips (deviated side/nondeviated side)
Ls Midpoint of the vermilion border of the upper lip
Li Midpoint of the vermilion border of the lower lip

The measurement of lip soft-tissue symmetry was based on a previous study, and the specific landmarks and measurement variables were shown in Figure 4 and Table Ι .

Soft-tissue model landmarks and measurement variables: A, landmarks: 1, Sbal-D; 2, Sbal-ND; 3, Cph-D; 4, Ls; 5, Cph-ND; 6, Ch-D; 7, Ch-ND; 8, Li; B, length measurements: a/a’ , length of philtrum crest (D/ND); b/b’ , length of upper lip vermilion (D/ND); c/c’ , length of Cupid's bow (D/ND); d/d’ , length of lower lip vermilion (D/ND); C, angle measurements: α/α’ , angle of Cupid's bow (D/ND); β/β’ , angle of the upper mouth (D/ND); γ/γ’ , angle of the lower mouth (D/ND); δ/δ’ , angle of the mouth (D/ND). D, the deviated side; ND , nondeviated side.
Fig 4
Soft-tissue model landmarks and measurement variables: A, landmarks: 1, Sbal-D; 2, Sbal-ND; 3, Cph-D; 4, Ls; 5, Cph-ND; 6, Ch-D; 7, Ch-ND; 8, Li; B, length measurements: a/a’ , length of philtrum crest (D/ND); b/b’ , length of upper lip vermilion (D/ND); c/c’ , length of Cupid's bow (D/ND); d/d’ , length of lower lip vermilion (D/ND); C, angle measurements: α/α’ , angle of Cupid's bow (D/ND); β/β’ , angle of the upper mouth (D/ND); γ/γ’ , angle of the lower mouth (D/ND); δ/δ’ , angle of the mouth (D/ND). D, the deviated side; ND , nondeviated side.

Statistical analysis

To control the study error, the first author located the landmarks twice at an interval of 2 weeks, and intraobserver reliability was analyzed statistically by intraclass correlation with 95% confidence intervals. The data were then imported into SPSS (version 26.0; IBM, Armonk, NY) for statistical analysis. A paired-sample t test was applied to compare the difference of the same variable before and after surgery. A Pearson correlation coefficient was used to evaluate the potential correlation between the changes in hard and soft-tissue variables at a significance level of 5%. To explore the important hard tissue variables influencing the lip soft-tissue changes, linear regression analysis was performed.

Results

A total of 30 patients were included in this study (12 males and 18 females; average age, 21.2 ± 3.5 years). The preoperative mandibular deviation range of this study was 5.87 ± 2.79 mm. The average mandibular setback was 5.21 ± 1.07 mm, and the average horizontal deviation correction was 4.90 ± 1.58 mm. The postoperative mandibular deviation range was 1.01 ± 0.96 mm. The high intraclass correlation value (range, 0.900-0.921) indicated good intraobserver reliability in this study. Measurement values of soft and hard tissue variables are shown in Table II .

Table II
Results of soft and hard tissue measurements
Measurement variables T1 T2 △T (T2 − T1)
a (mm) 12.59 ± 2.11 13.15 ± 2.07 1.41 ± 2.45
a’ (mm) 12.67 ± 2.02 13.19 ± 2.04 1.29 ± 2.56
b (mm) 24.92 ± 2.57 25.73 ± 2.27 0.81 ± 1.84
b’ (mm) 23.29 ± 1.37 25.20 ± 1.94 1.91 ± 1.669
c (mm) 6.54 ± 0.94 6.84 ± 1.14 0.31 ± 0.88
c’ (mm) 6.69 ± 1.01 6.69 ± 0.83 0.00 ± 0.65
d (mm) 27.64 ± 2.88 27.65 ± 2.39 0.01 ± 1.69
d’ (mm) 28.36 ± 2.03 27.61 ± 2.19 −0.75 ± 1.54
α (°) 130.19 ± 6.62 126.80 ± 5.72 0.42 ± 0.87
α’ (°) 124.84 ± 6.66 124.66 ± 6.48 −0.18 ± 4.17
β (°) 25.37 ± 5.85 26.78 ± 4.65 0.48 ± 0.77
β’ (°) 28.49 ± 5.85 27.69 ± 4.35 −3.40 ± 4.24
γ (°) 23.12 ± 3.53 21.83 ± 2.58 −0.80 ± 3.06
γ’ (°) 22.55 ± 3.12 21.88 ± 2.07 −0.67 ± 2.40
δ (°) 47.27 ± 8.48 47.70 ± 6.14 0.44 ± 4.19
δ’ (°) 49.99 ± 7.31 48.83 ± 5.72 −1.16 ± 4.11
Mid-X (mm) 5.87 ± 2.79 1.01 ± 0.96 −4.90 ± 1.58
Mid-Y (mm) 64.11 ± 3.45 62.56 ± 4.40 −1.56 ± 1.39
Mid-Z (mm) 45.14 ± 4.34 40.01 ± 4.21 −5.21 ± 1.07
T1, before orthognathic surgery; T2, 6 months after orthognathic surgery.

To investigate which symmetrical structure of the lips changed significantly after the surgery, a paired-sample t test was performed in this section. The results showed that the philtrum crests (a and a’) and vermilions of the upper lip of both sides (b and b’) became elongated postoperatively, accompanied by a shorter lower lip vermilion on the nondeviated side (d’) ( Table III ). In addition, significant changes were also observed in the angle of Cupid’s bow (α), the angle of the upper mouth (β), and the angle of the lower mouth (γ) on the deviated side.

Table III
Changes of lip measurement variables between T1 and T2
Measurement variables △T (T2 − T1) t P value
a (mm) 1.41 ± 2.45 −4.190 <0.001 ∗∗
a’ (mm) 1.29 ± 2.56 −3.322 0.002 ∗∗
b (mm) 0.81 ± 1.84 −2.428 0.022
b’ (mm) 1.91 ± 1.669 −6.215 <0.001 ∗∗
c (mm) 0.31 ± 0.88 −1.909 0.066
c’ (mm) 0.00 ± 0.65 −0.008 0.993
d (mm) 0.01 ± 1.69 −0.043 0.966
d’ (mm) −0.75 ± 1.54 2.665 0.012
α (°) 0.42 ± 0.87 4.382 <0.001 ∗∗
α’ (°) −0.18 ± 4.17 0.242 0.811
β (°) 0.48 ± 0.77 −3.158 0.004 ∗∗
β’ (°) −3.40 ± 4.24 1.437 0.161
γ (°) −0.80 ± 3.06 2.781 0.009 ∗∗
γ’ (°) −0.67 ± 2.40 1.538 0.135
δ (°) 0.44 ± 4.19 −0.572 0.572
δ’ (°) −1.16 ± 4.11 1.546 0.133
T1, before orthognathic surgery; T2, 6 months after orthognathic surgery.

P <0.05.

∗∗ P <0.01.

For the length of both sides of the upper and lower lips, only the preoperative philtrum crests and vermilion of the upper lip showed significant difference (a and b, D vs ND before orthognathic surgery; P <0.05), but this difference was not significant postoperatively (a and b, D vs ND 6 months after orthognathic surgery; P >0.05). A similar phenomenon was observed in the angle of α, γ, and δ, as is shown in Table IV .

Table IV
Difference between deviated and nondeviated side in T1 and T2
Measurement T1 T2
Variables D ND P value D ND P value
a (mm) 12.59 ± 2.11 12.67 ± 2.02 <0.001 ∗∗ 13.15 ± 2.07 13.19 ± 2.04 0.108
b (mm) 24.92 ± 2.57 23.29 ± 1.37 <0.001 ∗∗ 25.73 ± 2.27 25.20 ± 1.94 0.174
c (mm) 6.54 ± 0.94 6.69 ± 1.01 0.354 6.84 ± 1.14 6.69 ± 0.83 0.273
d (mm) 27.64 ± 2.88 28.36 ± 2.03 0.134 27.65 ± 2.39 27.61 ± 2.19 0.922
α (°) 130.19 ± 6.62 124.84 ± 6.66 <0.001 ∗∗ 126.80 ± 5.72 124.66 ± 6.48 0.386
β (°) 25.37 ± 5.85 28.49 ± 5.85 0.183 26.78 ± 4.65 27.69 ± 4.35 0.895
γ (°) 23.12 ± 3.53 22.55 ± 3.12 0.031 21.83 ± 2.58 21.88 ± 2.07 0.678
δ (°) 47.27 ± 8.48 49.99 ± 7.31 0.001 ∗∗ 47.70 ± 6.14 48.83 ± 5.72 0.058
T1, before orthognathic surgery; T2, 6 months after orthognathic surgery.

P <0.05.

∗∗ P <0.01.

Changes of bilateral philtrum crests (△a and △a’) were both positively correlated with the amount of horizontal deviation correction (△Mid-X), in which r = 0.439 and P <0.05 and r = 0.602 and P <0.01, respectively. Besides, the change of vermilion of the lower lip on the nondeviated side (△d’) was negatively correlated with △Mid-X ( r = −0.374; P <0.05). In terms of angular changes, only the angle of the lower lip on the deviated side (△γ) showed a significant correlation with △Mid-X ( r = 443; P <0.05). All remaining correlations were not significant ( Table V ).

Table V
Correlation between changes of soft and hard tissues
Soft tissue Hard tissue Pearson correlation coefficients
Variables (mm/°) Variables (mm) r P value
△a △Mid−X 0.439 0.015
△Mid−Y −0.002 0.992
△Mid−Z −0.131 0.492
△a’ △Mid−X 0.602 <0.001 ∗∗
△Mid−Y 0.106 0.565
△Mid−Z −0.259 0.176
△b △Mid−X 0.002 0.991
△Mid−Y 0.131 0.492
△Mid−Z −0.031 0.869
△b’ △Mid−X −0.139 0.463
△Mid−Y 0.061 0.750
△Mid−Z −0.002 0.993
△d’ △Mid−X −0.374 0.042
△Mid−Y −0.176 0.351
△Mid−Z 0.241 0.199
△α △Mid−X −0.238 0.206
△Mid−Y −0.160 0.397
△Mid−Z 0.025 0.894
△β △Mid−X 0.073 0.702
△Mid−Y −0.011 0.954
△Mid−Z −0.317 0.088
△γ △Mid−X 0.443 0.014
△Mid−Y 0.086 0.650
△Mid−Z 0.188 0.320

P <0.05.

∗∗ P <0.01.

Table VI exhibits the linear regression analysis results of the variables with significant associations described above. The 4 regression models are as follows:

Table VI
Liner regression analysis results for hard and soft variables
Variables Unstandardized coefficient Standardized coefficient Significance
Soft Hard B SE (β) t P value
△a Constant 1.522 0.424 3.591 0.001 ∗∗
△Mid-X 0.213 0.082 0.439 2.588 0.015
△a’ Constant 2.047 0.428 4.787 <0.001 ∗∗
△Mid-X 0.331 0.083 0.602 3.986 <0.001 ∗∗
△d’ Constant −2.545 0.882 −2.886 0.007 ∗∗
△Mid-X −0.366 0.171 −0.374 −2.134 0.042
△γ Constant 2.219 1.411 1.573 0.127
△Mid-X 0.717 0.274 0.443 2.615 0.014
SE , standard error.

P <0.05.

∗∗ P <0.01.

Model 1: △a = 1.522 + 0.213 ∗ △Mid-X

Model 2: △a’ = 2.047 + 0.331 ∗ △Mid-X

Model 3: △d’= −2.545 − 0.366 ∗ △Mid-X

Model 4: △γ = 0.717 ∗ △Mid-X

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