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Facial changes in patients with skeletal class III deformity after bimaxillary surgery: an evaluation based on three-dimensional photographs registered with computed tomography
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Orthodontics, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Digital stomatology Center, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Clinical Research Center for Oral Diseases, Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, 145 West Changle Road, Xi’an 710032, PR China
The objective of this study was to evaluate facial soft and hard tissue changes, individually and relative to each other, in patients with skeletal class III deformity after bimaxillary surgery using three-dimensional (3D) photos obtained by white light scanning. Thirty patients with skeletal class III deformity who underwent bimaxillary surgery were selected. Each patient underwent white light scanning and spiral computed tomography (CT) within two weeks before (T0) and six months after surgery (T1). The 3D photos were registered with CT soft tissue models for T0 and T1, and the skeletal area unaffected by treatment (cranial base) was used to register T0 and T1. Then, the 3D colour-coded map was analysed to assess both skeletal and soft tissue changes between T0 and T1. Changes in the 3D coordinates of each anatomical landmark were analysed using the Student’s t-test. Maxillary advancement by 2–3 mm and mandibular recession by 5–6 mm were observed; the mandible was shortened in the vertical direction. Compared with the preoperative values, the nasal columella was 0.51 mm shorter, the upper lip was 0.71 mm longer, the base of the alar cartilage was 1.38 mm wider, and the nasolabial angle became larger. The ratio of change in the position of soft tissue point Sn to hard tissue point A was 0.73:1, and that of soft tissue point Pg to hard tissue point Pog was 0.86:1. Images obtained by structured white light scanning registered with CT can be used as an alternative to study facial changes after orthognathic surgery.
Jaw deformity is a common clinical condition. With the improvement in quality of life over time, an increasing number of patients are seeking surgical treatment for jaw deformities to obtain normal occlusal function and enhance facial aesthetics.
Consequently, to evaluate the feasibility of treatment and to optimise case management, accurate prediction of hard and soft tissue changes is an important part of diagnosis and treatment planning in orthognathic surgery cases.
Although commonly used to study soft and hard tissue changes after orthognathic surgery with the highest spatial resolution, cone beam computed tomography (CBCT) has some disadvantages, including higher noise and lower contrast, compared with conventional medical CT systems, especially for 3D surface reconstruction.
The relationship between soft tissues and hard tissues after orthognathic surgery remains controversial owing to varying results, heterogeneity in research design and methods, and confounding variables.
Toward a higher accuracy in orthognathic surgery by using intraoperative computer navigation, 3D surgical guides, and/or customized osteosynthesis plates: a systematic review.
This retrospective study aimed to evaluate the ratio of soft-to-hard tissue changes in patients with skeletal class III malocclusion treated with bimaxillary surgery without genioplasty.
Material and methods
This study was performed in accordance with the Declaration of Helsinki and was approved by the appropriate review board. All patients provided written informed consent.
Research data
For this retrospective study, patients with skeletal class III malocclusion (retruded maxilla and protruded mandible) treated from August 2019 to June 2020 in a single centre were identified. The exclusion criteria were as follows: (1) severe facial asymmetry (menton deviation >4 mm), (2) increase or decrease in body weight by >2 kg before and after surgery, (3) body mass index >28 kg/m2, (4) craniofacial anomaly, (5) severe transverse discrepancies (>4 mm), and (6) age >35 years. All included patients underwent two-jaw orthognathic surgery with 3D computer-aided planning (intermediate/final wafer with plates adapted at the time). A combination of different degrees of maxillary advancement and posterior impaction using Le Fort I osteotomy and mandibular setback bilateral sagittal split ramus osteotomy (BSSRO) was adopted to achieve a normal dentoskeletal relationship. Each patient underwent nasal alar retraction suture with double silk fixed at the small hole of the anterior nasal ridge and V-Y lip lengthening. Finally, 30 patients (11 men and 19 women; mean [SD] age, 23.05 [3.52] years) were included in the study.
Research methods
Patients underwent a full skull CT (Philips Brilliance 64-slice spiral CT; scanning layer thickness: 1.25 mm) and 3D photo scanning (Artec Eva hand-held 3D scanner) within two weeks before surgery (T0) and six months after surgery (T1). The original CT-DICOM data were imported into CMF PROPLAN 3.0 (Materialise) software to reconstruct 3D hard-tissue and soft-tissue models. A space rectangular coordinate system was established by default in the CMF PROPLAN 3.0 software. The orientation of the skull model in the coordinate system was adjusted such that the line passing through the bilateral infraorbital margins and the Frankfurt plane and the line passing through the bilateral mastoid processes were parallel to the horizontal plane when viewed from the front, lateral, and bottom perspectives. The X-, Y-, and Z-axes were in the horizontal, vertical, and sagittal directions, respectively.
After processing with Artec studio 12.0 software, the 3D photos (T0/T1) were registered with the CT soft-tissue model (T0/T1) in CMF PROPLAN 3.0 software using the best fit surface-based superimposition. Then, T0 and T1 hard-tissue models that merged with 3D photos were registered in CMF PROPLAN 3.0 software using the best fit superimposition based on an unchanged anatomical site—the cranial base area (Fig. 1).
Fig. 1Fusion model generation process and registration. The three-dimensional photographs were registered with the computed tomographic soft-tissue model. Then, T0 and T1 hard-tissue models were registered by the best fit superimposition based on an unchanged anatomical site—the cranial base area.
In the CMF PROPLAN 3.0 software, 20 anatomical landmarks were assigned on the T0 and T1 3D photos, and 18 anatomical landmarks (Fig. 2) were assigned on the T0 and T1 3D hard-tissue models in the same coordinate system twice by the same researcher at 2-week intervals.
Toward a higher accuracy in orthognathic surgery by using intraoperative computer navigation, 3D surgical guides, and/or customized osteosynthesis plates: a systematic review.
The 3D coordinate value of each landmark was measured at pre- and post-operation, and changes in the coordinates (Xd, Yd, and Zd) were calculated. The soft-to-hard tissue movement ratios were evaluated in the anteroposterior axes.
The length of the columella (distance between Prn and Sn), height of the upper lip (distance between Sn and UL), and width of the alar cartilage (distance between Rac and Lac) were calculated before and after surgery.
Statistical analysis
All measurements were repeated after two weeks, and a paired t-test revealed no difference between the two assessments (p=0.101). Therefore, the second set of measurements was used. After confirming the normality of the data distribution using the Shapiro–Wilk test, a single sample t-test was conducted to analyse Xd, Yd, and Zd data using SPSS version 16.0, and p < 0.05 was considered statistically significant. Then, linear regression analysis was performed to analyse the sagittal changes in the corresponding points of soft and hard tissues, i.e. A-Sn, U1-UL, B-Si, and Pog-Pg.
Results
Qualitative analysis
When the maxilla was moved forward with Le Fort I surgery, both sides of the alar cartilage and upper lip area advanced, and the trend of the change decreased from the alar base to the periphery.
When the mandible retracted, the soft tissues in the chin area retracted, and the mentolabial sulcus and vermillion of the lip changed the most, with the effect decreasing toward the periphery (Fig. 3).
Fig. 3Facial soft tissue registration colour scale analysis before and after surgery. A patient’s three-dimensional image overlaps before and after surgery with frontal view/oblique side view. Different colours represent the change in distance. When the maxilla was advanced with Le Fort I surgery, both sides of the alar bone and the upper lip area became full, and the trend of change declined from the base of the alar bone to the periphery. When the mandible receded, the soft tissue in the chin area retracted, and the lip-chin groove and vermillion of the lip changed the most, with the changes decreasing toward the periphery.
The change in the soft tissues in the mandibular area was greater than that in the maxillary area; however, almost no change was observed in the width of the bilateral mandibular angle area. The overall height of the face became shorter after bimaxillary surgery.
Quantitative analysis
Skeletal tissue changes
Horizontal direction
Only the point ULfm near the buccal tip of the left first molar shifted toward the left significantly, with a mean (SD) value of 1.34 (1.49) mm. This may have been caused by random error.
Sagittal direction
Points A, PNS, U1, OrL, ULfm, and URca moved significantly forward; points L1, B, Pog, and Me moved significantly backward.
Vertical direction
Points L1, B, Pog, and Me moved significantly upwards.
Soft tissue changes
Horizontal direction
The mean (SD) basal width of the nasal airfoil widened by 1.36 (1.63) mm. There was a significant change in the left and right buccal points, with a mean (SD) width of 2.02 (2.58) mm between the two points.
Sagittal direction
Points A, Sn, Prn, Rac/Lac, and UL moved forward significantly. Among these, the mean (SD) point Sn repositioned by 2.08 (1.24) mm. The point Prn repositioned by a mean (SD) distance of 1.16 (0.82) mm. On the right, the point Rac repositioned by a mean (SD) 3.15 (1.80) mm, and the mean (SD) change in the position of the left nasal base was 2.79 (1.78) mm. The point UL repositioned by a mean (SD) of 1.23 (1.60) mm. Points B, Rch/Lch, ll, Si, Pg, and Mes showed significant retrogressive changes.
Vertical direction
Points UL, LL, Rch, Lch, Rchk, Lchk, Ren, and Len repositioned downwards significantly. Point Mes repositioned upwards significantly, with a mean (SD) value of 2.38 (2.86) mm.
Nasolabial area changes
After Le Fort I osteotomy and BSSRO, the length of the columella became shorter by mean (SD) 0.51 (0.68) mm, upper lip became longer by mean (SD) 0.71 (1.41) mm, and distance from the upper lip to nose tip became longer by mean (SD) 1.39 (2.37) mm. This indicated that the nasolabial angle increased. The distance from the nose tip to the base of the nose wing left/right was mean (SD) 0.74 (1.10) mm/0.95 (1.65) mm longer, which indicated that the width of nasal base was mean (SD) 1.38 (1.65) mm longer.
Association between hard and soft tissues
The soft-to-hard tissue movement ratios for different landmarks are shown in Figure 4. The ratio of soft-to-hard tissue movement for point Sn-to-point A was 0.73:1 and that of point Pg-to-Pog was 0.86:1. Correlation analysis of four pairs landmarks, A-Sn, U1-UL, B-Si and Pog-Pg are shown in Figure 5.
Fig. 4Changes in the proportion of soft and hard tissue markers. Soft tissue landmark movements (points Sn, U1, UL, Prn, RAC / Lac, II, Si, Pg, Mes; marked in blue) corresponding to 1 mm of each hard tissue landmark movement (points A, U1, L1, B, Pog, Me; marked in red).
Fig. 5Linear regression analysis of four pairs of landmarks: a. A-Sn, b.U1-UL, c. B-Si and d. Pog-Pg. The r value shows that correlation of B-Si and Pog-Pg was better than that of the other points, indicating that the correlation between the soft and hard tissue changes of the mandible is higher than that of the maxilla.
The cranio-maxillofacial-dental fusion model based on CT and optical scanning data of the dentition and facial soft tissues aids in the preoperative design, intraoperative verification, and postoperative analysis of orthognathic surgery.
In our study, 3D photos registered with CT were used to evaluate facial changes in patients with skeletal class III deformity after double-jaw surgery using anatomical landmarks.
Previously, clinicians used CT data to reconstruct facial soft tissues in 3D to evaluate changes after orthognathic surgery.
The accuracy of 3D reconstruction of facial soft tissues by CT scanning is determined by spatial resolution and density resolution. CBCT has the clearest image, with the highest spatial resolution of 2.6 line pair (lp)/mm, while spiral CT has a spatial resolution of 14.5–24 lp/cm, which is much lower than that of CBCT.
However, because of the low bulb voltage of CBCT, its density resolution is low; thus, the surface of the 3D model is noisy and rough, making it prone to interpretation errors.
To evaluate the soft and hard tissue changes, we adopted a fusion model—optical 3D soft tissue photos registered with skeletal tissues recorded using CT. Qualitative analysis and quantitative measurement confirmed that after Le Fort I osteotomy, changes in the nasolabial area especially in the nasal base, were the most significant, and gradually declined towards the periphery, probably because the osteotomy line is in the area where the connection between the bone and the muscles is tight; thus, the soft tissue buffer is reduced. However, there is no muscle attachment below the vestibular groove, and the upper lip is thicker than the nasolabial area; hence, the soft tissue buffer is greater. Soft tissue buffering prevents soft tissues from moving the same distance as skeletal tissues.
Several previous studies evaluated the relationship of soft-to-hard tissue movement, however, the results were variable.
Almeida et al analysed the anatomical area of the lower lip and chin based on the points identified on CBCT and showed that the ratio of change in the position of the lower lip to lower incisor was 95% and that in the position of the soft tissue to hard tissue pogonion was 87.3%, with a wide standard of error in measurements, thereby demonstrating variability in 3D results.
Jung et al showed that the relative ratio of the soft tissue to bony movement after BSSRO was only approximately 66% at the lower lip and 73% at soft tissue point B. In another study, in Le Fort I advancement, the ratio was 21% at the Ls point.
A clear ratio relationship cannot be inferred from these different methods and measurement results. The vertical analysis of the soft tissue to hard tissue ratio is complex. Horizontal movement can be better evaluated, in which the results of point B and soft tissue pogonion (90%–100% soft-to-hard tissue ratio) were shown to be more stable than other ratios in a previous study. More obvious changes were observed in the middle face ratio under the nose, i.e. point Sn-A (soft-to-hard tissue ratio, 60%–90%), and the tip of the first upper central incisor, i.e. point UL-U1 (soft-to-hard tissue ratio 65%–100%).
Here, to evaluate the change in the soft-to-hard tissue ratio, A-Sn, U1-UL, B-Si, and Pog-Pg were used for correlation analysis. The results showed that the correlation of B-Si and Pog-Pg was better than that of the other points, indicating that the correlation between the soft and hard tissue changes of the mandible was higher than that in the maxilla.
The nasolabial region greatly contributes to facial aesthetics. Le Fort I osteotomy significantly affects the nasal anatomy by increasing the width of the nasal base and changing the position of the nasal column and tip. Michelle et al showed that the width of the alar base significantly increased by 1.89 mm even though an alar cinch was placed.
Liu et al systematically reviewed the cinch surgery and found that modified alar cinch surgery can maintain the preoperative alar width better than traditional cinch surgery because it increases the anchorage of the underlying tissue.
However, an average alar widening of approximately 1.38 mm still occurred after surgery in our study. Additionally, the data of the present study showed that the postoperative width change in patients with wider nasal base before surgery was less than that of those with narrow nasal alar base, which indicates that the presurgical nasal anatomy affected the postsurgical appearance.
This study aimed to evaluate facial changes in patients with skeletal class III deformity after orthognathic surgery based on 3D photos registered with CT. The results provide guidance for the virtual design and planning of orthognathic surgery. However, this study inevitably may have had errors in measurements because of the limited sample size and manual errors in marking points. In future research, we aim to use the automated method for marking landmarks based on artificial intelligence and expand the sample size to obtain more accurate results.
Conclusions
Registration of 3D photos with CT is an alternative for the evaluation of facial changes in orthognathic surgery. In patients with skeletal class III deformity, the maxilla advanced, especially in the upper lip region beside the alar cartilage, and the mandible retracted, mainly in the chin region. The correlation between the soft and hard tissues of the mandible was higher than that in the maxilla, and the ratio of change in the soft and hard tissues of the chin was nearly linear.
Funding
This work was supported by an Independent Research Project of the State Key Laboratory of Military Stomatology [grant number 2017ZA02].
Conflict of interest
None.
Ethical approval
This study was performed in accordance with the Declaration of Helsinki and was approved by the regional Ethical Review Board of The Third Affiliated Hospital of Air Force Military Medical University (approval number IRB-YJ-2020010). All patients provided written informed consent.
Appendix A. Supplementary material
The following are the Supplementary data to this article:
Toward a higher accuracy in orthognathic surgery by using intraoperative computer navigation, 3D surgical guides, and/or customized osteosynthesis plates: a systematic review.
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