Abstract
Orthognathic surgery aims to improve both the function and facial appearance of the patient. Translation of the maxillomandibular complex for correction of malocclusion is always followed by changes to the covering soft tissues, especially the nose and lips. The purpose of this study was to evaluate the changes in the nasal region and upper lip due to orthognathic surgery using combined cone beam computed tomography (CBCT) and three-dimensional (3D) stereophotogrammetry datasets. Patients who underwent a Le Fort I osteotomy, with or without a bilateral sagittal split osteotomy, were included in this study. Pre- and postoperative documentation consisted of 3D stereophotogrammetry and CBCT scans. 3D measurements were performed on the combined datasets and analyzed. Anterior translation and clockwise pitching of the maxilla led to a significant volume increase in the lip. Cranial translation of the maxilla led to an increase in the alar width. The combination of CBCT DICOM data and 3D stereophotogrammetry proved to be useful in the 3D analysis of the maxillary hard tissue changes, as well as changes in the soft tissues. Measurements could be acquired and compared to investigate the influence of maxillary movement on the soft tissues of the nose and the upper lip.
Orthognathic surgery aims to improve the function and aesthetic facial appearance of the patient. To achieve optimal results, both aspects are crucial. Movement of the maxillomandibular complex for correction of malocclusion is always followed by changes to the covering soft tissues and therefore has an effect on aesthetics.
Predicting the changes to the soft tissue of the nose as a consequence of maxillomandibular surgery has been studied anthropometrically, two-dimensionally (2D) by means of direct or indirect plaster casts, using photographs, by lateral roentgen-cephalometry, and three-dimensionally (3D). The human body is a 3D entity and therefore any change, whether from movement during facial expression or from surgery, occurs in three dimensions.
The purpose of this study was to evaluate in 3D the changes to the nasal region (inter-alar width and nose volume) and upper lip volume as a consequence of orthognathic surgery.
Materials and methods
Patients
Patients (female, age >16 years; male, age >17 years) who underwent a Le Fort I osteotomy (with or without a simultaneous bilateral sagittal split osteotomy) between 2006 and 2010 were included. Exclusion criteria were the following: missing preoperative or postoperative 3D photograph or cone beam computed tomography (CBCT) scans, multi-segment Le Fort I osteotomy, anterior open bite cases, mandibular setback, alar cinch procedure performed, rhinoplasty surgery during or within 1 year after the Le Fort I osteotomy, and cases with other accompanying cranio-facial syndromes.
Pre- and postoperative 3D documentation
A CBCT scan (i-CAT System; Imaging Sciences International, Hatfield, PA, USA) was used to capture bony tissue information. A 3D stereophotogrammetry camera setup (3dMD System; 3dMD LLC, Atlanta, GA, USA) was used to capture 3D photographs of the face. The 3D photographs were generated from six 2D photographs taken simultaneously (four grey-scale photographs and two full colour photographs). A polygon light pattern was projected onto the four grey-scale photographs. Based on this pattern and its deformed image, a 3D photograph was reconstructed.
A full field of view extended height CBCT scan was acquired preoperatively and at 1 year postoperative. 3D photographs were acquired immediately preoperative and at 1 year postoperative.
3D measurements
Hard tissue maxillary changes
Both the CBCT and the 3D photographs were taken in natural head position and habitual occlusion. Patients were asked to relax their facial musculature, swallow, and keep their molars in normal occlusion after swallowing.
From the preoperative and postoperative CBCT scans, a 3D reconstruction (3D model) was created in Maxilim (Maxilim version 2.2.2.1; Medicim NV, Mechelen, Belgium). The postoperative 3D model was aligned with the preoperative model using a voxel-based matching procedure, as described by Nada et al. . The central incisor, right molar, and left molar landmarks were identified on the preoperative 3D model. These landmarks form a triangle on the preoperative maxilla. A Le Fort I osteotomy was performed digitally on the preoperative 3D model to separate the preoperative maxilla model from the skull base. The separated preoperative maxilla model was aligned with the postoperative 3D model again using voxel-based matching. In this way, a second triangle was acquired consisting of exactly the same points. For the preoperative and postoperative triangles, the centre of mass was calculated and the difference between the two triangles resulted in the translations and rotations of the maxilla ( Fig. 1 A) .
Nasal and lip changes
To isolate the region of interest (ROI) on the 3D photographs, the neck and parts of the hair were trimmed using 3dMD Patient Analysis version 3.1.0 software. A surface-based matching procedure for the pre- and postoperative 3D photographs was performed in five steps, as described by our group. A distance map was created on the matched 3D photographs indicating the soft tissue changes ( Fig. 1 B). Finally a modified 3D cephalometric analysis, based on a previously described 3D cephalometric soft tissue analysis of CT data ( Table 1 ), was performed. From this analysis, the inter-alar width and planes lining the nose and upper lip were acquired ( Fig. 2 ). The planes indicate the ROI, and the volumes of the nose and upper lip were calculated from this ROI.
| Landmark | Abbreviation | Description |
|---|---|---|
| Alare (left) | al(l) | Left alare, most lateral point on the left alar contour |
| Alare (right) | al(r) | Right alare, most lateral point on the right alar contour |
| Cheilion (left) | ch(l) | Left cheilion, point located at the left labial commissure |
| Cheilion (right) | ch(r) | Right cheilion, point located at the right labial commissure |
| Cheilion (middle) | ch(m) | Soft tissue point automatically computed as the midpoint of the right cheilion and left cheilion |
| Nasion | n | Midpoint of the frontonasal suture |
| Subnasale | sn | Midpoint on the nasolabial soft tissue contour between the columella crest and the upper lip |
| Crista philtrum (left) | cph(l) | The point at each crossing of the vermillion line and the elevated margin of the philtrum |
| Crista philtrum (right) | cph(r) | The point at each crossing of the vermillion line and the elevated margin of the philtrum |
| Crista philtrum (middle) | cph(m) | Soft tissue point automatically computed as the midpoint of crista philtrum left and crista philtrum right |
| Plane | Description |
|---|---|
| Median plane | The median ( z ) 3D reference plane is computed through the pupil reconstructed point and as a plane perpendicular to the horizontal ( x ) and the vertical ( y ) 3D reference planes |
| Horizontal plane | The horizontal ( x ) 3D reference plane is automatically computed as a plane 6.6° below the canthion–superaurale line, along the horizontal direction of the natural head position and through the pupil reconstructed point translated 77.2 mm more posteriorly |
| Vertical plane | The vertical ( y ) 3D reference plane is computed as a plane perpendicular to the horizontal ( x ) 3D reference plane and along the horizontal direction of the natural head position |
| Lateral left nasal plane | A plane through landmarks ch(l) and al(l) and perpendicular to the vertical plane |
| Lateral right nasal plane | A plane through landmarks ch(r) and al(r) and perpendicular to the vertical plane |
| Upper nasal plane | A plane through landmark n and parallel to the horizontal plane |
| Lower nasal plane | A plane through landmark sn and parallel to the horizontal plane |
| Upper lip plane | A plane through landmark cph(m) and parallel to the lower lip plane |
| Lower lip plane | A plane through landmark ch(m) and parallel to the horizontal plane |
Operative procedure
All surgical operations were performed or supervised by one of the authors (MdK). After nasotracheal intubation, the mucobuccal fold of the maxilla (and in bimaxillary cases also the mandible) was infiltrated with local anaesthetic (Ultracain DS Forte). The Le Fort I procedure was started with an incision in the gingivobuccal sulcus from the canine on one side to the canine on the other side. After elevation of the mucoperiosteum and nasal mucosa, the osteotomy line was designed with a fine burr, after which the osteotomy cut was made with a reciprocal saw. The lateral nasal walls and nasal septum were osteotomized with a nasal osteotome. The piriform aperture and when necessary the nasal spine was rounded. After mobilization of the maxilla, it was positioned in the planned position using an acrylic wafer. Fixation was performed with four 1.5-mm miniplates (KLS Martin, Tuttlingen, Germany), one paranasal and one on the buttresses on each side. The mucosa was closed with a 4-0 Vicryl suture (Ethicon; Johnson and Johnson Medical, Norderstedt, Germany); no alar cinch or V–Y closure was performed. Intraoperative antibiotics were given (1000 mg cefazolin and 500 mg metronidazole).
Statistical analysis
An intra- and inter-observer analysis was performed to evaluate the reproducibility of the landmarks used in the soft tissue analysis. The paired Student’s t -test was used for the statistical analysis, with a P -value of <0.05 indicating a statistical difference.
The preoperative and postoperative measurements were compared using the Student’s t -test. The influence of the maxillary translations and rotations on the soft tissue variables was investigated using linear regression analysis, with statistically significant differences indicated by a P -value of <0.05.
The statistical data analysis was performed using SPSS software, version 16.0 (SPSS Inc., Chicago, IL, USA).
Results
Patients
Thirty-six patients were included in this study (12 men and 24 women). The mean age was 26.9 years (range 17–55 years). Twelve (five men and seven women) underwent a Le Fort I osteotomy; the remaining 24 (seven men and 17 women) underwent a bimaxillary procedure.
Pre- and postoperative 3D documentation
CBCT and 3D photographs were acquired preoperatively and at 1 year postoperative (range 6–24 months).
3D measurements
The inter- and intra-observer analysis ( Table 2 ) showed no statistically significant differences.
| Paired differences | Significance (two-tailed) * | |||||
|---|---|---|---|---|---|---|
| Mean | SD | SEM | 95% CI of the difference | |||
| Lower | Upper | |||||
| Inter-observer | ||||||
| Vertical | −0.062 | 0.878 | 0.074 | −0.209 | 0.085 | 0.404 |
| Horizontal | 0.083 | 0.694 | 0.059 | −0.033 | 0.199 | 0.157 |
| Median | −0.017 | 0.892 | 0.075 | −0.166 | 0.132 | 0.822 |
| Euclidean distance | −0.077 | 0.647 | 0.055 | −0.185 | 0.032 | 0.164 |
| Intra-observer | ||||||
| Vertical | 0.064 | 0.663 | 0.056 | −0.047 | 0.175 | 0.254 |
| Horizontal | 0.020 | 0.554 | 0.047 | −0.073 | 0.112 | 0.673 |
| Median | 0.047 | 0.671 | 0.057 | −0.065 | 0.159 | 0.406 |
| Euclidean distance | 0.040 | 0.478 | 0.040 | −0.039 | 0.120 | 0.318 |
* Paired samples test; a P -value of <0.05 indicates a significant change.
The postoperative landmarks were significantly different from the preoperative landmarks ( P < 0.001). Table 3 shows the hard tissue landmarks split into their respective coordinates. The anterior translation changed significantly, while the other translations did not (central incisor: P < 0.001; left molar: P < 0.001; right molar: P < 0.001).
| Paired differences | Significance (two-tailed) * | |||||
|---|---|---|---|---|---|---|
| Mean | SD | SEM | 95% CI of the difference | |||
| Lower | Upper | |||||
| Hard tissue landmarks | ||||||
| Central incisor | ||||||
| Anterior translation (mm) | 3.36 | 1.90 | 0.31 | 2.73 | 3.98 | 0.00 |
| Cranial translation (mm) | 0.99 | 3.96 | 0.66 | −0.36 | 2.33 | 0.15 |
| Lateral right translation (mm) | −0.17 | 1.41 | 0.24 | −0.65 | 0.30 | 0.47 |
| Left molar | ||||||
| Anterior translation (mm) | 3.27 | 1.65 | 0.28 | 2.71 | 3.83 | 0.00 |
| Cranial translation (mm) | 0.46 | 2.33 | 0.39 | −0.33 | 1.25 | 0.25 |
| Lateral right translation (mm) | −0.11 | 0.90 | 0.15 | −0.41 | 0.19 | 0.47 |
| Right molar | ||||||
| Anterior translation (mm) | 3.23 | 1.84 | 0.31 | 2.61 | 3.86 | 0.00 |
| Cranial translation (mm) | 0.56 | 2.37 | 0.40 | −0.24 | 1.37 | 0.16 |
| Lateral right translation (mm) | −0.14 | 0.93 | 0.16 | −0.46 | 0.17 | 0.36 |
| Soft tissue measurements | ||||||
| Nose volume (mm 3 ) | 1203.58 | 1113.86 | 185.64 | 1580.46 | 826.71 | 0.00 |
| Lip volume (mm 3 ) | 2207.41 | 1979.52 | 329.92 | 2877.19 | 1537.64 | 0.00 |
| Inter-alar width (mm) | 1.76 | 1.02 | 0.17 | 2.11 | 1.42 | 0.00 |
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