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Volume Changes in Human Masticatory Muscles between Jaw Closing and Opening

¹ Department of Oral and Maxillofacial Radiology, Faculty of Dental Science, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan;
² Department of Radiology, Kyushu University Hospital, Fukuoka, Japan; and
³ Asahi Kasei Joho System Co., Ltd., Tokyo, Japan;

View larger version (136K): [in this window] [in a new window]   Figure 1. The high-quality 3D image sets of the entire head (A–C) and phantoms (D) obtained by means of 3D MP RAGE (TR 9.7 ms, TE 4.0 ms, TI 300 ms). The field of view was 230 x 230 mm. (A) Coronal view. LP, lateral pterygoid muscle; MP, medial pterygoid muscle; MS, masseter muscle. (B) Sagittal view. (C) Axial view. The voxels are 0.45 x 0.45 x 1.25 mm. They are displayed as a series of contiguous images at intervals of 1.25 mm. When the contour of difficult parts is traced on the original coronal images, the different sets of contiguous axial, sagittal, or other images are reconstructed and used to confirm the correct position of the muscle contour. (D) The empty space of the phantoms was filled with contrast medium consisting of 1.0 mmol/L gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA; Magnevist, Schering AG, Berlin, Germany). Transparent plastic wrap was used to hold the contrasting agents in the phantoms.

View larger version (30K): [in this window] [in a new window]   Figure 2. The ratio of muscle volume change after jaw opening to the volume at jaw closing: (opening – closing) x 100/closing (%). (A) Masseter muscle. (B) Medial pterygoid muscle. (C) Lateral pterygoid muscle. Female subjects, a–e; male subjects, f–j. A positive % indicates a greater volume during opening.

View larger version (136K): [in this window] [in a new window]   Figure 3. A typical three-dimensional reconstruction (surface rendering) of the traced masticatory muscles was made by means of Dr. View/PRO software (AJS Co., Ltd, Tokyo, Japan) on the OCTANE workstation (Silicon Graphics Co., Inc., Mountain View, CA, USA) at a jaw-closing position (A, the teeth in the dental intercuspal position) and at a jaw-opening position (B). Only two-dimensional coronal and lateral views of the three-dimensional reconstruction are shown here. The morphological changes, such as the length and cross-sectional size, can be observed after jaw opening. Moreover, the heterogeneity between and within each muscle is demonstrated.

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