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ISSN : 1225-1577(Print)
ISSN : 2384-0900(Online)
The Korean Journal of Oral and Maxillofacial Pathology Vol.44 No.3 pp.77-83
DOI : https://doi.org/10.17779/KAOMP.2020.44.3.002

Angle and Distance for Measuring Menton Deviation in Facial Asymmetry Analysis

Mun Hwan JIn1), In-Ja Song2), Jae-Seo Lee3), Byung-Cheol Kang3), Eun Joo Lee4), Hyeon-Shik Hwang5), Suk-Ja Yoon3)*
1)School of Dentistry, Chonnam National University
2)Department of Nursing, Kwangju Women’s University
3)Department of Oral and Maxillofacial Radiology, School of Dentistry, Dental Science Research Institute, Chonnam National University
4)Department of Oral Anatomy, School of Dentistry, Dental Science Research Institute, Chonnam National University
5)Department of Orthodontics, School of Dentistry, Chonnam National University
*Correspondence: Suk-Ja Yoon, Department of Oral and Maxillofacial Radiology, School of Dentistry, Chonnma National University, 33 Yongbongro Bukgu Gwangju, 61186 South Korea Tel: +82-62-530-5680, Fax: +82-62-530-5848 E-mail: yoonfr@chonnam.ac.kr
May 15, 2020 May 29, 2020 June 5, 2020

Abstract


Menton (Me) deviation is commonly used for diagnosing facial asymmetry. This study compared angle and distance measurement in determining the severity of Me deviation for facial asymmetry diagnosis. Three-Dimensional Computed Tomographic(3D CT) images of 32 patients (mean age 22.5yrs, SD 3.4yrs; 16 male, 16 female) with facial asymmetry were selected for this study. Angle and distance of Me deviation in each patient were obtained and the severity of Me deviation was determined according to the angle and the distance measurement. The severity of Me deviation by angle and distance measurement was compared and statistical analysis was performed. Eight (25%) showed disagreement in severity of Me deviation between the two measurements. The kappa coefficient on the two measurements was 0.67, showing substantial agreement. It is suggested that both angle and distance measurement be performed in determining severity of Me deivation.


Facial asymmetry , Menton , Computed tomography

안면비대칭 정도를 결정하는 Menton 편위의 각도와 거리 측정

진 문환1), 송 인자2), 이 재서3), 강 병철3), 이 은주4), 황 현식5), 윤 숙자3)*
1)전남대학교 치의학전문대학원
2)광주여자대학교 간호학과
3)전남대학교 치의학전문대학원 구강악안면방사선학교실, 치의학연구소
4)전남대학교 치의학전문대학원 구강해부학교실, 치의학연구소
5)전남대학교 치의학전문대학원 교정학교실

초록

    Ⅰ. INTRODUCTION

    Recently social interests in facial esthetics increases, following the increasing number of patients searching for facial esthetic improvement. Therefore, orthodontic treatments have developed to meet such desires. Patients who visit orthodontic departments receive treatment for teeth crowding, maxillary protrusion, mandibular prognathism, facial asymmetry, and facial growth defect. Dentists occasionally have patients with a chief complaint of facial asymmetry. Dentists have traditionally used posteroanterior cephalometry for determining the degree of facial asymmetry. Menton (Me) has been a critical landmark for determining the degree of facial asymmetry1-3).

    Conventional two-dimensional (2D) radiography has inherent shortcomings such as image distortion, superimposition, and magnification2-10). In contrast three-dimensional computed tomography (3D CT) visualize 3D human face in any angle, providing .provides accurate measurement of angle and distance on the face2,5,10-21).

    Angle and distance measurement for determining the degree of Me deviation have been introduced. One method measures the distance between Me and facial midline3). The other measures the angle between the facial midline and the line connecting anterior nasal spine (ANS) and Me4). Two measurements are mainly used for diagnosis. The diagnosis can differ depending on the measurements for diagnosis of facial asymmetry. However, there has been no research that compares the two measurements.

    The purpose of this study was to investigate the difference between angle and distance measurement in determining facial asymmetry.

    Ⅱ. MATERIALS AND METHODS

    Thirty two orthodontic patients (mean age 22.5yrs, SD 3.4yrs; 16 male, 16 female) who underwent orthognathic surgery between the year 2000 and 2007 were reviewed for this study.

    CT scans were taken with a spiral CT scanner (Light speed QX/I, GE Medical Systems, Milwaukee, WI, USA). The patient was positioned on the table with Frankfurt line perpendicular to the floor. The imaging parameters were set at 120kV, 200mA, 512×512 matrix, and a gantry angle of zero. The axial image slice was 2.5mm. The table speed was 3mm/s, and the scanning time was 0.8s. The field of view was 18cm, covering the superior of the orbit and the entire mandible. Digital Imaging and Communication in Medicine images (DICOM) were created at a slice thickness of 1.0mm. The acquired data from these images were transferred to a personal computer, and the CT data were used to construct 3D images with the software Vworks + Vsurgery (Cybermed, Seoul, Korea). The surface shaded display was obtained at a threshold value of 126.

    Three reference planes were established midsagittal reference plane (MRC) connecting Cg, ANS and OP. Horizontal reference plane (HRP) was formed with left porion (Po) and right orbitale (Or) to be perpendicular to MRP. The coronal reference plane (CRP) was formed perpendicular to both HRP and MRP and passing through Dent. (Fig. 1, Table 1)2,5).

    In angle measurement, Me deviation was considered to be normal when the angle (x1) between the lines connecting Me with ANS and the MRP were less than 2° (0°≤x1<2°); mild when less than 4° (2°≤x1<4°); moderate when less than 8° (4°≤x1<8°); and severe at 8° or higher (8°≤x1)4).

    In distance measurement, Me deviation was determined to be normal when the distance (x2) between Me and MRP was less than 2mm (0mm≤x2<2mm); mild when less than 4mm (2mm≤x2<4mm); moderate when less than 8mm (4mm ≤x2<8mm); and severe at 8mm or higher (8mm≤x2)3).

    Statistical analysis

    The correlation between angle and distance measurement was analyzed. Cohen’s kappa coefficient determined whether the two degrees of facial asymmetry corresponded to each other. Statistical analysis was performed by IBM SPSS 1.0.0.642 (IBM Corp, USA).

    Ⅲ. RESULTS

    The mean of the angle between the facial midline and the line connecting ANS and Me was 4.89°±3.38°. The patients were 10 (31.25%) in the normal group, 4 (12.5%) in the mild group, 12 (37.5%) in the moderate group, and 6 (18.75%) in the severe group. From the results for distance measurement between Me and facial midline, mean value was 6.15 mm ± 4.40mm(Table 2). Seven patients (21.87%) were in normal group, 7 (21.87%) in mild. 8 (25%) in moderate, and 10 (34.37%) in severe. Twenty-four (75%) showed agreement in the two measurements, while 8 (25%) showed disagreement between the two measurements. Among 10 patients in the normal group on angle measurement, 3 (30%) were grouped into the mild group on distance measurement. Four patients in the mild group on angle measurement were all grouped into the mild group on distance measurement(100% agreement). Among 12 patients in the moderate group on angle measurement, 5 (41.66%) were grouped into the severe group on distance measurement. Among 6 patients in the severe group on angle measurement, 1 (16.67%) were grouped into the moderate group on distance measurement. The kappa coefficient of the severity of Me deviation on two method was 0.67 (p<.05), showing substantial agreement between the two measurements (Table 2 and 3).

    Ⅳ. DISCUSSION

    Me has diagnostic significance in determining facial asymmetry. Two methods to measure the degree of Me deviation have been used. One measures the distance between Me and facial midline. The other measures the angle between the facial midline from line connecting ANS and Me. However, there has been no research comparing the two methods. The purpose of this study was to investigate differences between distance and angle measurement in determining facial asymmetry.

    Lee et al.7) suggested statistically significant differences between PA and CT in Me deviation. Difference between PA cephalogram and 3D CT was attributed by several factors. Firstly, the landmarks (Lo and Lo’) did not appear on the human skull. Lo is the intermeasurement between the oblique orbital line and the lateral contour of the orbit. The oblique orbital line is the radiopaque image of the greater wing of the sphenoid bone, projected onto the orbit when a conventional cephalogram is taken. Nc is a point on PA cephalograms, but it is not a point on the 3D anatomy and it does not really exist. Secondly, the distortion and magnification of anatomical structure on PA were unavoidable. We agree that three-dimensional analysis by CT for determining the degree of Me deviation is more accurate than PA radiography.

    The number of patients showing agreement in the measurements of distance and angle was 24 (75%), while disagreement was found in 8 (25%). The two measurements showed substantial agreement (kappa 0.67, p<.05)(Table 2 and 3).

    The results in this study are very natural and expectable. Even when angle between the facial midline from line connecting ANS and Me is the same, if Me is vertically differently located, the distance differs. If two persons have the same angle of the Me deviation but different vertical location of the Me, a person with shorter face has shorter distance of the Me deviation than the other person with longer face. As an example, the patient 6 on Table 2 showed 1.55° angle of Me deviation, and the patient 7 showed 1.62°; but the patient 6 showed 2.11 mm distance of Me deviation, and the patient 7 showed 1.76 mm distance, shorter than the patient 6. As a results, the patient 6 and 7 were grouped into the normal group in angle measurement, while the patient 6 was grouped into the mild group in distance measurement and the patient 7 the normal group. This suggests that the patient 6 have longer face than the patient 7(Table 2).

    Twenty-four patients (75%) showed agreement in grouping of the asymmetry between the angle and distance measurement of Me deviation. Among 10 patients in the normal group on angle measurement, 3 (30%) were grouped into the mild group on distance measurement. Four patients in the mild group on angle measurement were all grouped into the mild group on distance measurement(100% agreement). Among 12 patients in the moderate group on angle measurement, 5 (41.66%) were grouped into the severe group on distance measurement. Among 6 patients in the severe group on angle measurement, 1 (16.67%) were grouped into the moderate group on distance measurement(Table 3).

    This study used 3D CT of patients for comparing the angle and distance measurement for determining the degree facial asymmetry. If the same study is done using PA cephalograms, the same results might be obtained, showing disagreement between angle and distance measurement in some patients.

    Measurement of Me deviation might be affected by how MRP was created. There are two methods of creating MRP. In one method, HRP is first established using three landmarks, such as Lo, Lo’, Nc18,20,22,24), and then MRP is created perpendicularly to the HRP. In such cases, MRP is affected by HRP. The other method establishes MRP using three midfacial landmarks such as Cg, ANS and Op2,5,6,17,22,23). In this study, MRP passing through Cg, ANS and Op, HRP was created perpendicular to MRP passing through right Or and Po, and CRP was made with Dent to be perpendicular to both MRP and HRP5).

    In conclusion, this study compared two methods of measuring the degree of Me deviation; One measures the distance between Me and facial midline, and the other measures the angle between the facial midline from line connecting ANS and Me. The same angle of Me deviation does not mean the same distance, and the same distance of Me deviation does not mean the same angle, because the vertical location of Me might be various. According to the method of determining Me deviation, angle or distance measurement, the grouping of the asymmetry might show differences. Therefore, considering only either one method between angle or distance, makes different results of patient grouping in facial asymmetry from the other method. It is recommended to make a diagnosis considering both of them, angle and distance of Me deviation.

    Figure

    KAOMP-44-3-77_F1.gif

    Menton deviation measured on 3DCT. A. Three reference planes were established and landmarks were defined. B. A schematic drawing of the angle and distance measured in this study.

    Table

    Landmarks and planes used for this study

    Distance and angle measurement of Me deviation in the patients

    The severity of Me deviation according to the angle and distance measurement on 3DCT

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