Abstract
This study employed the cone-beam computed tomography (CBCT) superimposition method to evaluate postoperative midfacial soft-tissue changes in cases of skeletal Class III malocclusion after double-jaw surgery with setback and vertical reduction Le Fort I osteotomy. A retrospective study was carried out on 15 patients who had undergone maxillary setback Le Fort I osteotomy and mandibular setback sagittal split ramus osteotomy with alar cinch suturing and V-Y soft-tissue closure. Three dimensional CBCT volume scans were recorded preoperatively (T0) and 6 months postoperatively (T1) to measure soft-tissue changes of the upper lip and midface. Post-surgery, soft-tissue landmarks in the cheek and paranasal areas had moved forward; the soft-tissue thickness at the A-point had markedly increased ( P < 0.05); there was no significant change in the subnasale, and the midline of the soft-tissue of the upper-lip area had moved backward. The extent of the mean soft-tissue change at the labrale superius was greater than that at the other soft-tissue landmarks of the upper lip. The results suggest that maxillary setback movement of the maxilla by alar cinch suturing has a beneficial effect on paranasal soft-tissue and lip contours for patients with protrusive lip and acute nasolabial angle.
Attractive facial aesthetics, in addition to oral functionality, is a major treatment goal of orthodontics and orthognathic surgery. Nomura et al. reported that in a study on lip position aesthetics, all groups preferred lip positions posterior to the E-line. Although the race and gender of patients and judges, in part, determined those preferences. Generally, East Asians have a greater tendency to bimaxillary or bialveolar protrusion than Caucasians. Bimaxillary-retrusion female profiles are perceived to be the most attractive, and excessive lip protrusion the least attractive, in Asians. Given such preferences, it is important that surgeons have the ability to predict treatment outcomes that achieve patients’ aesthetic goals.
As regards soft-tissue response, there are many reports in the literature about hard- and soft-tissue changes after orthognathic surgery. Despite this, the association between skeletal and soft-tissue movements following maxillary setback in cases of skeletal Class III malocclusion is poorly understood. While analyses of maxillary setback have been based on two dimensional (2D) lateral cephalograms, a clear picture of the midfacial soft-to-hard tissue response after maxillary setback movement requires three dimensional (3D) analysis, due to the geometry of the human face. Among several 3D analysis strategies, cone-beam computed tomography (CBCT), notably offers simultaneous access to the facial soft tissue and the underlying skeletal structure. Additionally, voxel-based superimposition, working from a stable reference structure, can provide surgeons with accurate information on treatment-related facial changes.
In the treatment of skeletal Class III deformity with maxillary vertical excess, Le Fort I osteotomy has been performed for maxillary superior repositioning. Kim et al. reported anterior movement of the soft tissue in the triangular area bounded by the nasolabial grooves and the upper lip. Maxillary superior movement in double-jaw surgery can adversely affect the upper-lip position and related areas in patients with normal anteroposterior maxillary position. To prevent lip protrusion, the maxillary position should be set posteriorly, but exactly how maxillary posterior movement affects midfacial soft-tissue changes remains unclear.
The purpose of the present study was to evaluate, by CBCT superimposition, the postoperative soft-tissue changes in the midfacial areas of skeletal Class III malocclusion patients after double-jaw surgery with setback and vertical reduction Le Fort I osteotomy.
Materials and methods
This was a retrospective study. The subjects consisted of 15 adults (6 men, 9 women; mean age 22.8 ± 3.2 years) presenting with skeletal Class III malocclusion. All of the patients had undergone maxillary setback Le Fort I osteotomy and mandibular setback sagittal split ramus osteotomy by a single surgeon. The isolated maxilla was set by rigid internal fixation involving the standard alar cinch suturing technique and V-Y soft-tissue closure. Prior to the operation, callipers were used to record the alar base width accurately. The suture was passed through the fibroadipose tissue at the alar base. Once in place, it was tightened until the pre-treatment width of the alar base was achieved. Non-absorbable 3/0 suture was used. The incision was closed with a single 5–7 mm V-Y soft-tissue closure on the midline of the upper lip (instead of continuous closure). Additional surgery, which can cause changes in the midfacial soft tissue during or after treatment, was not undertaken. This study was reviewed and approved by the Institutional Review Board of Pusan National University Hospital (E2012024).
CBCT assessment
A CBCT machine (Pax-Zenith 3D, Vatech Co., Seoul, Korea) was used to analyse the hard- and soft-tissue changes. CBCT scans were recorded preoperatively (T0, 1 month before surgery) and postoperatively (T1, 6 months after surgery), with the subject in an upright position for maximum intercuspation. The Frankfort horizontal (FH) plane of the patients was parallel to the floor. The maxillofacial regions were scanned using a CBCT machine with a field of view of 20 cm × 19 cm, a tube voltage of 110 kVp, a tube current of 5.0 mA, and a scan time of 24 s. The resultant images were reconstructed as 3D versions using 3D imaging software (Ondemand3D, Cybermed Co., Seoul, Korea).
To analyse the hard- and soft-tissue measurement points, the new superimposition method, applying the mutual information theory to automatic voxel-by-voxel registration with subvoxel accuracy, was employed ( Fig. 1 ). The anterior cranial base was used as the stable reference structure for CBCT superimposition. The landmarks and reference planes are indicated and described in Fig. 2 and Tables 1 and 2 . The extents of hard- and soft-tissue changes for the measurement points at the T0 and T1 stages were measured by a single investigator using imaging software. The differences between the T0 and T1 images were calculated by CBCT superimposition.
| Reference points and planes | Description |
|---|---|
| Porion (Po) | Most superior point of external auditory meatus |
| Orbitale (Or) | Most inferior point of infraorbital margin |
| Basion (Ba) | Most posterior inferior point of occipital bone at anterior margin of foramen magnum |
| Nasion (Na) | Most anterior point of frontonasal suture on midsagittal plane |
| Frankfort horizontal (FH) plane | Plane formed by both sides of Po and non-affected side of Or |
| Midsagittal reference (MSR) plane | Plane perpendicular to FH plane and passing through Na and Ba |
| Superior horizontal (SH) plane | Plane parallel to FH plane and passing through lowest point of orbit |
| Inferior horizontal (IH) plane | Plane parallel to FH plane and passing through inferior border of zygomaticomaxillary suture |
| Middle horizontal (MH) plane | Plane bisecting SH and IH planes |
| Inner sagittal (IS) plane | Plane parallel to midsagittal plane and passing through outer rim of piriform aperture |
| Lateral sagittal (LS) plane | Plane parallel to FH plane and passing through lateral border of orbit |
| Middle sagittal (MS) plane | Plane bisecting IS and LS planes |
| Soft-tissue landmarks | Description |
|---|---|
| 11/21 (Rt/Lt) | Intersecting soft-tissue point between SH and IS planes |
| 12/22 (Rt/Lt) | Intersecting soft-tissue point between SH and MS planes |
| 13/23 (Rt/Lt) | Intersecting soft-tissue point between SH and LS planes |
| 14/24 (Rt/Lt) | Intersecting soft-tissue point between MH and IS planes |
| 15/25 (Rt/Lt) | Intersecting soft-tissue point between MH and MS planes |
| 16/26 (Rt/Lt) | Intersecting soft-tissue point between MH and LS planes |
| 17/27 (Rt/Lt) | Intersecting soft-tissue point between IH and IS planes |
| 18/28 (Rt/Lt) | Intersecting soft-tissue point between IH and MS planes |
| 19/29 (Rt/Lt) | Intersecting soft-tissue point between IH and LS planes |
| 31 subnasale | Midpoint of angle at columella base where lower border of nasal septum and surface of upper lip meet |
| 32/33 subalare (Rt/Lt) | Point at lower limit of each alar base, where alar base disappears into skin of upper lip |
| 35/36 cheilion (Rt/Lt) | Point located at each labial commissure |
| 34 labrale superius | Midpoint of upper vermilion line |
| 38/39 (Rt/Lt) | Soft-tissue midpoint between points 32/33 and 35/36 (Rt/Lt) |
| 37 | Soft-tissue midpoint between points 31 and 34 |
Statistical analysis
For intra-observer CBCT reliability, all of the measurements were repeated, by the same investigator, after 2 weeks, and the mean of the two measurements was used in the statistical analysis. The reliability subsequently was confirmed on the basis of Cronbach coefficient α . Non-parametric Wilcoxon signed rank tests were conducted to compare the measurement differences between the T0 and T1 stages. These were considered to be significant at P < 0.05. All of the analyses were performed with SPSS software version 12.0 (SPSS Inc., Chicago, IL, USA).
Results
In the results, the intra-observer agreement between the T0 and T1 stages was excellent (Cronbach coefficient α range 0.956–0.999). The average distance from the coronal vertical reference plane to the A-point, in the assessment of the extent of maxillary setback movement between T0 and T1, was 3.63 ± 3.49 mm. The average of the upward maxillary movement at the A-point was 3.31 ± 1.29 mm. The average backward mandibular movement was 7.25 ± 2.37 mm ( P < 0.05) ( Table 3 ).
| Mean | SD | P -Value | |
|---|---|---|---|
| Maxillary movement | |||
| Setback | 3.63 | 3.49 | 0.000 * |
| Upward | 3.31 | 1.29 | 0.000 * |
| Mandibular movement | |||
| Setback | 7.25 | 2.37 | 0.000 * |
* Significant difference by Wilcoxon signed rank test ( P < 0.05).
The means and standard deviations of the soft-tissue measurement differences between T0 and T1 were calculated ( Table 4 ). The soft-tissue landmarks in the cheek (landmarks 17, 18, 24, 27, 28) moved forward after surgery. Forward movement was shown also at the soft-tissue landmarks in the paranasal areas (landmarks 32, 33). The soft-tissue thickness at the A-point was significantly increased after surgery. There was no significant change at the subnasale (landmark 31). The midline of the soft tissue of the upper-lip area (34, 37) moved backward after maxillary setback surgery. The extent of the mean soft-tissue change at the labrale superius (34) was greater than that at landmark 37 ( Fig. 3 and Table 4 ).
| Soft-tissue change | |||
|---|---|---|---|
| Landmarks (mm) | Mean | SD | P-value |
| 11 (Rt. intersection between SH and IS planes) | −0.126 | 4.013 | 0.346 |
| 12 (Rt. intersection between SH and MS planes) | −0.052 | 3.281 | 1.000 |
| 13 (Rt. intersection between SH and LS planes) | 0.405 | 3.687 | 0.432 |
| 14 (Rt. intersection between MH and IS planes) | 1.213 | 3.316 | 0.084 |
| 15 (Rt. intersection between MH and MS planes) | 1.665 | 3.758 | 0.084 |
| 16 (Rt. intersection between MH and LS planes) | 0.854 | 2.891 | 0.202 |
| 17 (Rt. intersection between IH and IS planes) | 2.543 | 4.045 | 0.022 * |
| 18 (Rt. intersection between IH and MS planes) | 1.894 | 3.945 | 0.084 * |
| 19 (Rt. intersection between IH and LS planes) | 1.686 | 4.191 | 0.136 |
| 21 (Lt. intersection between SH and IS planes) | 0.091 | 3.493 | 0.556 |
| 22 (Lt. intersection between SH and MS planes) | −0.196 | 3.020 | 0.937 |
| 23 (Lt. intersection between SH and LS planes) | 1.495 | 4.307 | 0.099 |
| 24 (Lt. intersection between MH and IS planes) | 2.189 | 3.637 | 0.028 * |
| 25 (Lt. intersection between MH and MS planes) | 0.890 | 3.166 | 0.239 |
| 26 (Lt. intersection between MH and LS planes) | 1.543 | 4.628 | 0.878 |
| 27 (Lt. intersection between IH and IS planes) | 2.636 | 4.097 | 0.018 * |
| 28 (Lt. intersection between IH and MS planes) | 3.027 | 4.120 | 0.018 * |
| 29 (Lt. intersection between IH and LS planes) | 0.981 | 2.528 | 0.223 |
| 31 (Subnasale) | 0.378 | 4.142 | 0.875 |
| 32 (Rt. Subalare) | 3.800 | 4.998 | 0.018 * |
| 33 (Lt. Subalare) | 2.971 | 1.487 | 0.002 * |
| 34 (Labrale superius) | −5.092 | 6.658 | 0.018 * |
| 35 (Rt Cheilion) | −1.643 | 7.674 | 0.388 |
| 36 (Lt. Cheilion) | −2.632 | 5.114 | 0.116 |
| 37 (Midpoint between subnasale and labrale superius) | −4.015 | 2.706 | 0.002 * |
| 38 (Rt midpoint between Rt. subalare and cheilion) | 0.435 | 5.687 | 0.906 |
| 39 (Lt. midpoint between Lt. subalare and cheilion) | −0.126 | 4.013 | 0.346 |
| Soft-tissue thickness at A-point | 4.765 | 4.326 | 0.007 * |
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