Three-dimensional Assessment of Facial Soft Tissue after Orthognathic Surgery in Patients with Skeletal Class III and Asymmetry

pISSN:1225-4207 eISSN: 2233-7296

Original Article

RECEIVED September 13, 2013, REVISED October 1, 2013, ACCEPTED November 26, 2013 Correspondence to Insan Jang

Department of Orthodontics, College of Dentistry, Gangneung-Wonju National University 7 Jukheon-gil, Gangneung 210-702, Korea

Tel: 82-33-640-2762, Fax: 82-33-640-3057, E-mail: [email protected]

CC

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/

by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Three-dimensional Assessment of Facial Soft Tissue after Orthognathic Surgery in Patients with Skeletal

Class III and Asymmetry

Jong-Hyeon Lee, Dong-Soon Choi, Bong-Kuen Cha, Young-Wook Park ¹ , Insan Jang

Departments of Orthodontics and

Oral and Maxillofacial Surgery, College of Dentistry, Gangneung-Wonju National University

Abstract

Purpose: The purpose of this study was to perform three-dimensional (3D) assessment of facial soft tissue in patients with skeletal Class III and mandibular asymmetry after orthognathic surgery.

Methods: Samples consisted of 3D facial images obtained from five patients with A point-nasion-B point angle less than 2 degrees, and more than 5 mm of menton deviation. All patients had been treated at Gangneung-Wonju National University Dental Hospital from 2009 to 2012. They had undergone orthognathic surgery of Lefort I, and sagittal split osteotomy for correction of skeletal deformity, and orthodontic treatment. Facial scanning was performed before treatment (T1) and post-surgical orthodontic treatment (T2). Linear and angle variables of soft tissue landmarks, antero-posterior facial depth, and facial volume were measured.

Results: No significant differences in width of the alar base, mouth width, and nasal canting were observed between T1 and T2. However, lip deviation, menton deviation, alar canting, lip canting, and menton deviation angle were significantly reduced at T2. Antero-posterior facial depth on the axial plane parallel to the left cheilion was significantly reduced on the deviated side and significantly increased on the non-deviated side at T2. Volume of the lower lateral and lower medial parts of the face was reduced on the deviated side, and volume of upper lateral and lower lateral parts on the non-deviated side was significantly increased at T2.

Conclusion: After orthognathic surgery, facial asymmetry of soft tissue was improved following skeletal changes, especially the mandibular region. Although the length of the alar base and mouth width did not change, lip and soft tissue menton were displaced to the medial side after treatment. Facial depth also became symmetric after treatment. Facial volume showed a decrease on the lower part of the deviated side and that on lateral parts of the non-deviated side showed an increase after treatment.

Key words: Three-dimensional imaging, Laser scanning, Facial asymmetry, Orthognathic surgery

Introduction

The profile of facial soft tissue could be changed by orthodontic treatment or orthognathic surgery. Especially

in patients with skeletal deformity and asymmetry, facial

soft tissue after orthognathic surgery is definitely different

from that of before treatment. Conventionally, facial soft

tissue has been evaluated by cephalograms or photographs

Table 1. Cephalometric measurements of the patients (n=5) Variable Before treatment

(T1) After treatment (T2) SNA (

)

SNB (

)

Mx 1 to FH plane (mm) IMPA (

)

Mandibular plane angle (

) Menton deviation (mm)

78.5 78.1 113.8 88.6 28.9 10.7

79.4 77.2 116.9 91.3 30.7 3.4 SNA, sella-nasion-A point angle; SNB, sella-nasion-B point angle;

Mx 1, axis of maxillary central incisor; FH plane, Frankfort horizontal plane; IMPA, lower incisor-mandibular plane angle.

taken from frontal or sagittal views, from that, only the facial profile projected on a two-dimensional plane can be detected[1]. These methods have limitations for assess- ment of soft tissue that changes with complexity and three-dimensionally[2].

Several techniques[3-8], such as three-dimensional (3D) photogrammetry, laser surface scanning, and cone-beam computed tomography (CBCT), have been developed for 3D analysis of soft-tissue. However, patients’ heads are usually held with a strap on the forehead or a chin support, or patients are lying down when taking CBCT, which caus- es deformation of soft tissue of the forehead, chin, or lips.

On the other hand, the 3D surface scanning system is non- invasive to patients, and is an alternative for generation of 3D computerized images providing 3D information on soft tissue without deformity on the forehead, chin, or lips by a strap or chin support.

3D analysis of facial soft tissue has been attempted in patients who had undergone maxillofacial surgery[6,9-11].

Soncul and Bamber[6] evaluated facial soft tissue of patients with skeletal Class III and dentoskeletal deformity after orthognathic surgery; however, facial symmetry was not assessed. Hajeer et al .[9], Sforza et al .[10,11] analyzed sym- metry of facial soft tissue after surgery with mirror image or evaluated the linear and angular variables on the coronal plane.

Few previous studies evaluating the symmetry of facial soft tissue after orthognathic surgery in 3D planes and the effect of skeletal movement on the maxillary and man- dibular facial soft tissue have been reported. The purpose of this study was to perform 3D assessment of facial soft tissue in patients with skeletal Class III and mandibular asymmetry after orthodontic and orthognathic surgery.

Materials and Methods

1. Patients

Samples consisted of 3D facial images obtained from five patients (two females, three males) with skeletal Class III and moderate to severe asymmetry in the mandible.

All patients had been treated at Gangneung-Wonju National University Dental Hospital from 2009 to 2012. Inclusion criteria were as follows: (1) adult patients; (2) A point-nasio-

na-B point angle was less than 2

; (3) menton was deviated more than 5 mm on the postero-anterior cephalograms;

and (4) patients had undergone pre-surgical orthodontic treatment, Lefort I osteotomy and sagittal split osteotomy with mandibular reduction for correction of the skeletal deformity, and post-surgical orthodontic treatment. Mean age of patients before treatment was 18.6 years, and two of them had deviation of the mandible to the right and the others to the left. Data from cephalometric analysis before treatment (T1) and after post-surgical orthodontic treatment (T2) are shown in Table 1. This study was re- viewed and approved by the Institutional Review Board at the Gangneung-Wonju National University Dental Hospital (IRB 2010-1-7), and was supported by Scientific Research (SR1001) of Gangneung-Wonju National University Dental Hospital.

2. Three-dimensional facial scanning

Facial scanning was performed at T1 and T2 using a Rexcan III 3D scanner (Solutionix Corp., Seoul, Korea).

The scanning system consisted of two high resolution charge coupled device cameras. Focal length of the camera lens was 12.5 mm and the cameras were placed 1,340 mm from the patients. The patients were instructed to lean back in their chairs while relaxed, lips in slight contact, and eyes lightly closed. Their faces were scanned from frontal and lateral views in order to avoid undercut.

Scanning data were merged and 3D facial images were reconstructed using ezScan software (Solutionix Corp.). The 3D images were imported as stereolithography (STL) files to the reverse modeling software program, RapidForm XOR/REDESIGN 3 (INUS Technology Inc., Seoul, Korea) for superimposition and measurement.

The 3D facial images at T1 and T2 were initially super-

Fig. 1. Reference area for superimposition of three-dimensional facial images.

Fig. 2. Coordinate system of a three-dimensional facial image.

A, axial reference plane; B, saggital reference plane; C, coronal reference plane; N', soft tissue nasion.

Fig. 3. Soft tissue landmarks used in this study. N’, soft tissue nasion; prn, pronasale; sn, subnasale; ls, labilae superius; li, labilae inferius; me, soft tissue menton; Rt. ex, right exocanthion;

Lt. ex, left exocanthion; Rt. tr, right tragion; Lt. tr, left tragion;

Rt. al, right alare; Lt. al, left alare; Rt. ch, right cheilion; Lt. ch, left cheilion.

imposed on five landmarks of the bilateral outer and inner canthus of the eyes and the soft tissue nasion. Fine registra- tion was performed on the forehead and nasal root area, including soft tissue nasion using the best-fit method, where they were considered stable after orthodontic treat- ment and orthognathic surgery (Fig. 1). As shown in Fig.

2, the coordinate system was established on 3D facial im- ages of T1 with the soft tissue nasion (N’) as the origin (0, 0, 0). The axial plane was established by rotation and translation of Camper’s plane[12]. First, Camper’s plane passing through the nasal alar and bilateral tragus was ro- tated 7.5

upward on the axis formed by the bilateral

tragus. Subsequently, the plane was translated to pass through N’. The sagittal plane was defined as the plane perpendicular to the axial plane and passing though N’

and the midpoint of the bilateral tragus. The coronal plane passed through N’, and perpendicular to the axial and sag- ittal planes (Fig. 2).

3. Measurements on three-dimensional facial images

As shown in Fig. 3, the soft tissue landmarks were identi- fied on 3D images. Identification of landmarks and meas- urements was performed by one examiner (L.J.H.). The following variables were measured for quantification of asymmetry of facial soft tissue: (1) the five linear and four angular variables on the coronal plane; (2) the ante- ro-posterior facial depth on the axial plane; and (3) volume of facial soft tissue.

Alar base width, upper lip deviation, mouth width, lower

lip deviation, menton deviation, nasal canting, alar canting,

lip canting, and menton deviation angle were measured

on the coronal plane (Fig. 4, Table 2). The 3D geometry

of the lower facial third was constructed and divided into

upper lateral (UL), upper medial (UM), lower lateral (LL),

and lower medial (LM) parts (Fig. 5). Antero-posterior fa-

cial depth was measured on two planes parallel to the

axial plane passing through the subnasale (plane A), and

Fig. 4. Linear (A) and angular (B) variables on the coronal plane. a, alar base width; b, upper lip deviation;

c, mouth width; d, lower lip deviation;

e, menton deviation; f, nasal canting;

g, alar canting; h, lip canting; i, menton deviation angle.

Table 2. Linear and angular measuring variables on the coronal plane

Variable Definition

Linear measurements (mm) Alar base width

Mouth width Upper lip deviation

Lower lip deviation

Menton deviation

Angular measurements (

) Nasal canting

Alar canting

Lip canting

Menton deviation angle

Distance from alare to the sagittal reference plane Distance from cheilion to the sagittal reference plane The variable in the x axis of labiale superius The variable in the x axis of labiale inferius The variable in the x axis of soft tissue menton

Angle between the line connecting nasion and pronasale and the sagittal reference plane Angle between the line connecting bilateral alares and the axial reference plane

Angle between the line connecting bilateral cheilions and the axial horizontal plane Angle between the line connecting subnasale and menton and the sagittal reference plane

a

Positive value indicates deviation to the deviated side, and negative to the non-deviated side.

Positive value indicates canting with the deviated side up, and negative means non-deviated side up.

the plane passing through the left cheilion (plane B).

Volume of the 3D geometries of UL, UM, LL, and LM was measured, and the asymmetry index, which was defined as the following formula, was calculated. The closer to zero of the asymmetry index, the more symmetric the facial volume is: Asymmetry index=(volume of deviated side–vol- ume of non-deviated side)/(volume of deviated side+vol- ume of non-deviated side)×100.

All measurements are expressed as mean, and the Wilcoxon signed rank test was used for comparison of the measurement at T1 and T2, and for comparison of the deviated and non-deviated sides. Statistical analyses were performed using SPSS software (PASW Statistics 18.0;

IBM Co., Armonk, NY, USA) and probability values less than 0.05 were considered statistically significant.

Results

Although the width of the alar base showed a significant increase on the deviated side at T2, no significant difference in the width of the alar base on the non-deviated side and mouth width on the deviated and non-deviated sides was observed between T1 and T2. Mean of upper and lower lip deviation was 1.7 mm and 4.4 mm at T1 and showed a significant decrease at T2 as 0.7 mm, 1.6 mm.

Menton deviation also showed a definite reduction at T2,

from 10.2 to 2.9 mm (Table 3). Nasal canting was close

to zero at T1 and T2. The other angular measurements

of alar canting, lip canting, and menton deviation angle

showed a significant decrease at T2. However, lip canting

and menton deviation angle was 1.1

and 2.0

at T2, which

means that facial asymmetry had still left to the deviated

side (Table 4).

Fig. 5. Three-dimensional (3D) geometries of the lower facial third.

(A) 3D geometries of upper lateral (UL), upper medial (UM), lower lateral (LL), lower medial (LM). (B, C) Facial depth measured on plane A and plane B; plane C, the plane perpendicular to sagittal and axial reference planes and 40 mm posterior to the left orbitale; plane D and plane E, bilateral planes parallel and 40 mm apart from the sagittal reference plane; a~f, facial depth on the deviated side, center, and non-deviated side.

Table 3. Linear measurements of soft tissue landmarks (mm)

Variable T1 T2 P -value

Alar base width Deviated side Non deviated side Mouth width Deviated side Non deviated side Upper lip deviation

Lower lip deviation

Menton deviation

19.2 18.9 27.4 21.3 1.7 4.4 10.2

20.2 19.7 25.1 23.3 0.7 1.6 2.9

* NS NS NS

*

*

*

*P＜0.05.

T1, before treatment; T2, after treatment; NS, not significant.

a

Positive value indicates deviation to the deviated side.

Table 4. Angular measurements of soft tissue landmarks (

)

Variable T1 T2 P -value

Nasal canting

Alar canting

Lip canting

Menton deviation angle

0.0 1.9 2.8 8.2

󰠏0.1 0.1 1.1 2.0

NS

*

*

*

*P＜0.05.

T1, before treatment; T2, after treatment; NS, not significant.

a

Positive value indicates deviated side up.

Positive value indicates non-deviated side up.

Table 5. Antero-posterior facial depth (mm)

Variable T1 T2 P -value

Upper region Deviated side Center

Non deviated side Lower region Deviated side Center

Non deviated side

38.2 52.2 38.6 38.8 55.1 34.6

39.3 53.9 40.5 36.8 54.5 36.0

NS

* NS

* NS

*

*P＜0.05.

T1, before treatment; T2, after treatment; NS, not significant.

Antero-posterior facial depth on the plane A center showed a significant increase at T2, while no significant difference in depth on the deviated side and non-deviated side was observed between T1 and T2. On plane B, ante- ro-posterior depth showed a decrease on the deviated side and that on the non-deviated side showed a significant increase (Table 5).

Volumes of UL and UM at T1 were not significantly differ-

ent from those at T2, except UL on the non-deviated side,

Table 7. Asymmetry index (%)

Variable T1 T2

Upper lateral Upper medial Lower lateral Lower medial

7.8 0.7 34.5 10.4

󰠏6.1 0.0 8.4 4.2 Positive value indicates that volume on the deviated side is larger than that on the non-deviated side.

T1, before treatment; T2, after treatment.

Table 6. Volume of facial soft tissue (mm

)

Variable T1 T2 P-value

Upper lateral Deviated side Non deviated side Upper medial Deviated side Non deviated side Lower lateral Deviated side Non deviated side Lower medial Deviated side Non deviated side

16,294 13,939 46,981 46,306 13,865 6,746 83,140 67,416

16,500 18,651 46,950 46,946 11,500 9,717 73,985 68,039

NS

* NS NS

*

*

* NS

*P＜0.05.

T1, before treatment; T2, after treatment; NS, not significant.

which showed an increase at T2. On the other hand, LL and LM showed definite change in volume at T2. Volume of LL and LM showed a decrease on the deviated side, and that on the LL on the non-deviated side showed a significant increase at T2. In addition, volumetric difference between the deviated and non-deviated side was reduced at T2 on the LL and LM (Table 6). Asymmetry index shown in Table 7 indicates volumetric differences between de- viated and non-deviated sides. Asymmetry index of LL was 34.5%, which was the largest at T1 and it was 8.4% at T2. Asymmetry index of UM was near zero at T1 and T2.

All indexes were less than 10% at T2.

Discussion

The focus of this study was on evaluation of asymmetry in facial soft tissue, so that patients with severe facial asym- metry who had undergone bimaxillary orthognathic sur- gery for correction of canting of maxilla and mandibular deformity were included. Asymmetry of facial soft tissue before and after orthognathic surgery was evaluated quanti- tatively and three-dimensionally by measuring the linear and angular variables on the coronal plane, facial depth on the axial plane, and volume of facial soft tissue.

Mean of sella-nasion-A point angle increased by approx- imately 1

after treatment, meaning that the maxilla was advanced by Lefort I orthognathic surgery. This may result in the tendency of increasing the alar base width and facial depth near the subnasale after treatment (Table 3, 5).

Contrary to alar base width, mouth width was maintained.

Although most angular variables assessing symmetry of soft

tissue showed definite improvement after treatment, asym- metry had still been left to the deviated side. Deviation of the lower lip and menton had been left and lip canting was also observed after treatment. Of particular interest, menton was deviated by 3.4 mm on postero-anterior ceph- alograms after treatment, and soft tissue menton was also deviated by approximately 2.9 mm on 3D images. In the current study, soft tissue was likely to follow skeletal move- ment with the ratio of almost 85%, which was similar to those of other reports of 88%[13] and 84%[14]. Although the average duration of 13 months between T1 and T2 was considered sufficient for adaptation of muscle to a new position, the ratio of movement between soft tissue and skeleton did not increase.

Most previous reports had evaluated facial asymmetry in coronal planes, not in axial planes. We measured the antero-posterior depth on the axial plane passing the sub- nasale (plane A) and lips (plane B). It was interesting to note that the facial depth before treatment was almost sym- metric near the subnasale, even in patients with severe mandibular asymmetry. Asymmetric facial depth was found near the lips (plane B) and it became symmetric after treat- ment by decreasing on the deviated side and increasing on the non-deviated side. Soncul and Bamber[6] stated that the effect of maxillary movement decreases on the lateral part of facial soft tissue, as the maxilla has a semicircular shape and orbicularis oris muscle attached near the center of the maxilla and mandible. This is concurrent with our results showing that the facial depth on plane A increased significantly only at the center, not on the bilateral sides.

The 3D geometry of facial soft tissue was divided into

upper and lower parts of lips, as they are thought to be

susceptible to maxillary and mandibular movements,

respectively. As expected, facial volume was decreased

on the deviated side and increased on the non-deviated

side, and soft tissue became symmetric after treatment.

Although the volume of the UL region on the non-deviated side increased after treatment, volumetric change was not considerable on the upper region. The LL part of facial soft tissue displaced most sensitively to the orthognathic surgery with the asymmetry index of 34.5%.

In the current study, the linear and angular variables were selected as the variables relating to the facial asymme- try reported in other studies[12,15]. However, the linear and angular variables are landmark-dependent, which have limitations such as errors in identification of landmarks, and questionable validity of the midsaggital plane in asym- metric patients[16]. In addition, assessment of asymmetry is difficult where the landmarks are far between. For exam- ple, even if bilateral landmarks such as gonion are located symmetrically, the bilateral facial soft tissue of the inferior border of the mandible could be asymmetric. Consequently, we also measured facial depth and volume, which is land- mark-independent. Several previous studies have measured facial volume. Sforza et al .[10] measured the volumes of facial structures calculated as the sum of several tetrahedra, with the 50 landmarks serving as nodes. In their study, volume of tetrahedra was sensitive to identification of landmarks. Kobayashi et al .[17] calculated facial volume from two pairs of photographs. They reported that volu- metric change in the mandible was significant but not in the maxillary region after orthognathic surgery, which is in disagreement with our results for the maxillary region.

It may be that they assessed skeletal Class III patients;

however, in our study, more severe asymmetry was ob- served in patients whose maxilla was expected to move more after surgery. In the current study, the reference plane for the coordinate system was modified from another re- port[18]. The posterior and bilateral sagittal boundary planes of the 3D geometry were 40 mm apart from the orbitale, because one fourth of transverse width and half of the antero-posterior depth (nasion-tragus) were approx- imately 40 mm in Korean adults with normal occlusion[12].

Conclusion

3D assessment of asymmetry of facial soft tissue was performed successfully using the 3D surface scanning system. After orthognathic surgery, facial asymmetry of soft

tissue was improved following skeletal changes, especially the mandibular region. Length of the alar base and mouth did not change after treatment. However, lip, soft tissue menton was displaced to the medial side. Facial depth also became symmetric on the deviated and non-deviated side after treatment. Facial volume on the lower part of the deviated side decreased and that on lateral parts of the non-deviated side increased after treatment. The LL side of facial soft tissue showed sensitive displacement to the orthognathic surgery.

References

1. Edler R, Wertheim D, Greenhill D. Comparison of radio- graphic and photographic measurement of mandibular asymmetry. Am J Orthod Dentofacial Orthop 2003;123:167-74.

2. Moyers RE, Bookstein FL. The inappropriateness of conven- tional cephalometrics. Am J Orthod 1979;75:599-617.

3. Almeida RC, Cevidanes LH, Carvalho FA, et al . Soft tissue re- sponse to mandibular advancement using 3D CBCT scanning.

Int J Oral Maxillofac Surg 2011;40:353-9.

4. Ras F, Habets LL, van Ginkel FC, Prahl-Andersen B. Three-di- mensional evaluation of facial asymmetry in cleft lip and palate. Cleft Palate Craniofac J 1994;31:116-21.

5. Kawai T, Natsume N, Shibata H, Yamamoto T. Three-dimen- sional analysis of facial morphology using moiré stripes. Part I. Method. Int J Oral Maxillofac Surg 1990;19:356-8.

6. Soncul M, Bamber MA. Evaluation of facial soft tissue changes with optical surface scan after surgical correction of Class III deformities. J Oral Maxillofac Surg 2004;62:1331-40.

7. Moss JP, Linney AD, Grindrod SR, Arridge SR, Clifton JS.

Three-dimensional visualization of the face and skull using computerized tomography and laser scanning techniques. Eur J Orthod 1987;9:247-53.

8. Ayoub A, Garrahy A, Hood C, et al . Validation of a vi- sion-based, three-dimensional facial imaging system. Cleft Palate Craniofac J 2003;40:523-9.

9. Hajeer MY, Ayoub AF, Millett DT. Three-dimensional assess- ment of facial soft-tissue asymmetry before and after orthog- nathic surgery. Br J Oral Maxillofac Surg 2004;42:396-404.

10. Sforza C, Peretta R, Grandi G, Ferronato G, Ferrario VF. Soft tissue facial volumes and shape in skeletal Class III patients before and after orthognathic surgery treatment. J Plast Reconstr Aesthet Surg 2007;60:130-8.

11. Sforza C, Peretta R, Grandi G, Ferronato G, Ferrario VF.

Three-dimensional facial morphometry in skeletal Class III patients. A non-invasive study of soft-tissue changes before and after orthognathic surgery. Br J Oral Maxillofac Surg 2007;

45:138-44.

12. Baik HS, Jeon JM, Lee HJ. Facial soft-tissue analysis of Korean adults with normal occlusion using a 3-dimensional laser scanner. Am J Orthod Dentofacial Orthop 2007;131:759-66.

13. Lee JY. Soft tissue changes in relation to hard tissue changes of

the facial asymmetry orthognathic surgery patients using a 3-di-

mensional CT. [Master's thesis]. Seoul: Yonsei University; 2007.

14. Kim WS, Lee KH, Hwang HS. Comparison of asymmetric de- gree between maxillofacial hard and soft tissue in facial asym- metric subjects using three-dimensional computed tomography.

Korean J Orthod 2005;35:163-73.

15. Ercan I, Ozdemir ST, Etoz A, et al . Facial asymmetry in young healthy subjects evaluated by statistical shape analysis. J Anat 2008;213:663-9.

16. Hartmann J, Meyer-Marcotty P, Benz M, Häusler G, Stellzig-Eisenhauer A. Reliability of a method for computing facial symmetry plane and degree of asymmetry based on

3D-data. J Orofac Orthop 2007;68:477-90.

17. Kobayashi T, Ueda K, Honma K, Sasakura H, Hanada K, Nakajima T. Three-dimensional analysis of facial morphology before and after orthognathic surgery. J Craniomaxillofac Surg 1990;18:68-73.

18. Ferrario VF, Sforza C, Schmitz JH, Miani A Jr, Serrao G. A

three-dimensional computerized mesh diagram analysis and its

application in soft tissue facial morphometry. Am J Orthod

Dentofacial Orthop 1998;114:404-13.