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Size and Orientation of Masticatory Muscles in Patients with Mandibular Laterognathism

¹ Department of Oral and Maxillofacial Radiology, Faculty of Dental Science, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan;
² Faculty of Dental Science, Kyushu University, Fukuoka, Japan;
³ Asahi Kasei Information Systems Co., Ltd., Tokyo, Japan;
⁴ Department of Functional Anatomy, Academic Centre for Dentistry Amsterdam (ACTA), Universiteit van Amsterdam, and Vrije Universiteit Amsterdam, Netherlands;
⁵ Department of Medical Technology, Kyushu University Hospital, Fukuoka, Japan; and
⁶ Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan

View larger version (74K): [in a new window]   Figure 1. Methods in size measurements (cross-sectional area, length, and volume) and orientation of the masticatory muscles. (A) Reconstruction of MR images and individual jaw muscles: masseter (green), medial pterygoid (orange), and lateral pterygoid (red). Two different participants are shown, with the patient on the left as an experimental subject and the control on the right. (B) Reconstructed images showing the sagittal angle of the right jaw muscles. Horizontal lines are parallel to the Frankfort horizontal plane. Oblique lines represent the long axes of the muscles. Angle between the two lines describes the sagittal orientation of the muscles. (C) Coronal (masseter and medial pterygoid) and axial (lateral pterygoid) scans, showing the orientation in the respective planes. Horizontal lines are parallel to the Frankfort horizontal plane. Abbreviations: MS, masseter muscle; MP, medial pterygoid muscle; LP, lateral pterygoid muscle.

View larger version (34K): [in a new window]   Figure 2. Maximum cross-sectional areas (cm2), muscle length (mm), muscle volume (cm3), and orientations (°) of masseter, medial, and lateral pterygoid muscles, respectively. Patient group, n = 20, for each deviated or non-deviated side of 20 patients; control group, n = 10 (mean of both sides of 10 people). Dev, deviated side; Non-dev, non-deviated side. *p < 0.05 by t test with Bonferroni. **p < 0.01 by t test with Bonferroni. p < 0.01 by paired t test with Bonferroni. Significant differences between each side in patients and controls were seen. A marked difference in muscle volume is evident. Abbreviations: CSA, maximum cross-sectional area (cm2); Length, muscle length (mm); Volume, muscle volume (cm3); Angle, orientation (°).

View larger version (29K): [in a new window]   Figure 3. Normalized graphs (for both maximum cross-sectional area and muscle length) of cross-sectional areas in relation to muscle length. Data points for 20 muscles from both sides of 10 control participants are shown in the right panel. Data points for each deviated or non-deviated side of 20 participants are shown in the left panels. The dispersion of data-points indicates the variation in muscle morphology among participants. The crossbar shows the position at which the maximum cross-sectional area (mean) was located. Numbers in parentheses show the coefficient of variation (COV = SD/mean x 100%) of the relative position of the maximum cross-sectional area.