Analysis of masseter muscle in facial asymmetry before and after orthognathic surgery using 3-dimensional computed tomography

Seung-ah Seo; Hyoung-seon Baik; Chung-ju Hwang; Hyung-Seog Yu

doi:10.4041/kjod.2009.39.1.18

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Seo, Baik, Hwang, and Yu: Analysis of masseter muscle in facial asymmetry before and after orthognathic surgery using 3-dimensional computed tomography

Original Article

Korean Journal of Orthodontics

Korean Journal of Orthodontics 2009; 39(1): 18-27.

Published online: 28 February 2009

DOI: https://doi.org/10.4041/kjod.2009.39.1.18

Analysis of masseter muscle in facial asymmetry before and after orthognathic surgery using 3-dimensional computed tomography

Seung-ah Seo, DDS, MSD^a, Hyoung-seon Baik, DDS, MSD, PhD^b, Chung-ju Hwang, DDS, MSD, PhD^b, Hyung-Seog Yu, DDS, MSD, PhD^c

^aGraduate student. Department of Orthodontics, College of Dentistry, Yonsei University, Korea.

^bProfessor, Department of Orthodontics, College of Dentistry, Oral Science Research Institute, The Institute of Cranio-facial Deformity, Yonsei University, Korea.

^cAssociate Professor, Department of Orthodontics, College of Dentistry, Oral Science Research Institute, The Institute of Cranio-facial Deformity, Yonsei University, Korea.

Corresponding author: Hyung-Seog Yu. Department of Orthodontics, College of Dentistry, Yonsei University, 250, Seongsanno, Seodaemun-gu, Seoul 120-752, Korea. +82 2 2228 3104; yumichael@yuhs.ac

Received 22 August 2008 Revised 10 December 2008 Accepted 15 December 2008

Abstract

Objective

The purpose of this study was to understand the differences in masseter muscle (MM) between the shifted and non-shifted sides in facial asymmetry patients, and the changes shown by MM after mandibular surgery.

Methods

Pre- and post-operative CT scans were performed on 12 Class III patients with facial asymmetry who were treated by intraoral vertical ramus osteotomy and 10 subjects with normal occlusion. Using the V-works 4.0 program (Cybermed, Seoul, Korea), 3-dimensional images of the mandible, and MM were reconstructed, and evaluated.

Results

In the asymmetry group, the MM angle between the shifted and non-shifted sides was only significantly different (p < 0.05). Compared with normal occlusion, the asymmetry group showed a significantly smaller volume and maximum cross-sectional area in both sides of MM (p < 0.05). After mandibular surgery, the angle of MM (p < 0.01) and differences in angle between the shifted and non-shifted sides of MM (p < 0.05) were significantly decreased. The thickness in the maximum cross-sectional area was significantly increased (p < 0.01). After surgery, MM in facial asymmetry patients was similarly changed to those in the normal occlusion group except for widths.

Conclusions

MM in facial asymmetry was definitely different from those in normal occlusion. However, this study suggests that MM changed symmetrically in conjunction with the mandible after proper mandibular surgery.

Keywords: Masseter muscle, Facial asymmetry, Mandibular setback osteotomy, Normal occlusion, Thre dimensional computed tomography (3D CT)

Figures and Tables

Fig 1

Measurement of total volume, maximum cross-sectional area in axial view of the masseter muscle and thickness of the maximum cross sectional area.

Fig 2

Measurement of the masseter muscle angle.

Fig 3

Measurement of maximum cross-sectional area on a section perpendicular to the direction of the masseter muscle. a, Maximum area of masseter muscle; a₀, cross-sectional area measured on an axial image; θ, angle between the axial image and the section perpendicular to the muscle direction.

Table 1

Comparison of masseter muscle measurements between shifted side and non-shifted side of the asymmetry group

Vol, Volume of masseter muscle; Angle, direction angle of masseter muscle; Area, maximum cross sectional area of masseter muscle; D, distance from maximum cross sectional area to occlusion of upper & lower second molar; T, thickness of maximum cross sectional area; L, length of masseter muscle; W, width of masseter muscle. ^*p < 0.05; NS, not significant; Sig, significance.

Table 2

Comparison of masseter muscle measurements in normal occlusion and pre-operative asymmetry groups

The same abbreviation as Table 1. ^*p < 0.05; ^†p < 0.01. Min, minimum; Max, maximum; NS, not significant; Sig, significance.

Table 3

Changes in the masseter muscle measurements between pre and post operative stage

Pre-op, Pre operative stage; Post-op, post operative stage; -shift, measurement in shifted side; -nonshift, measurement in non-shifted side; -diff, difference between shifted and non-shifted side (shift-nonshift); -diff (%), (Vol-shift - Vol-nonshift) / (Vol-shift + Vol-nonshift) × 100 (%). ^*p < 0.05, ^†p < 0.01. Min, minimum; Max, maximum; Sig, significance; NS, not significant.

Table 4

Comparison of masseter muscle measurements in normal occlusion and post operative asymmetry groups

The same abbreviation as Table 1. ^*p < 0.05; ^†p < 0.01. Min, minimum; Max, maximum; Sig, significance; NS, not significant.

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