Korean J Orthod.  2009 Feb;39(1):18-27. 10.4041/kjod.2009.39.1.18.

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

• Seo SA
• Baik HS
• Hwang CJ
• Yu HS

• KMID: 1469135
• DOI: http://doi.org/10.4041/kjod.2009.39.1.18

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.

Keyword

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

MeSH Terms

Facial Asymmetry
Humans
Mandible
Masseter Muscle
Orthognathic Surgery
Osteotomy

Figure

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  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.

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  Fig 2 Measurement of the masseter muscle angle.

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  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.

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