Title Analysis of the mandibular movement by simultaneous multisection continuous ultrafast MRI

Purpose: Using simultaneous multi-cross sectional imaging, four cross sections, including the mandibular midline and the right and left temporomandibular joints, were imaged to observe one movement of mouth opening and closing and analyze the movement of the mandible and temporomandibular joints. Materials and Methods: Four cross sections, including the midsagittal section of the mandible, the sagittal sections of the right and left temporomandibular joints and the horizontal section containing the heads of right and left temporomandibular joints, were imaged simultaneously. The imaging was conducted in ten male and female volunteers. Results: In all volunteers, the relationship of the mandibular movement on the median line with the right and left temporomandibular joints was observed. Images of the volunteers with trismus indicated the condition in which the right and left temporomandibular joints did not move in keeping with each other but moved independently from each other. Conclusion: Complex movement of the temporomandibular joint was first evaluated by simultaneous multiple-cross sectional MRI for the movement of mandible and temporomandibular joints. Introduction The mandibular movement was conventionally measured by positioning indices on the skull surface; i.e., the movement of the temporomandibular joints was measured indirectly. This method can directly measure a tracing of the incisor point but not the mandibular movement [1] [2] [3] [4]. In contrast, MRI provides observation of any section and images of the articular disk soft tissue without radiation exposure and is very effective for observing the temporomandibular joints [5] [6]. MRI provides semi-movement images of articular tissues, but not continuous images. On opening and closing of the mouth (mandible) halfway, MR images are taken in several steps under the condition that the volunteers stop for several minutes with a spacer in their mouth. Based on a series of these static images, the movement can be measured [7] [8]. However, this cannot be considered to be an actual reproduction of movement. We therefore continuously visualized one side of the temporomandibular joints in opening and closing of the mouth by ultrafast imaging (Turbo-FLASH) in analyzable resolution and in real time and we used this data to measure the movement of the temporomandibular joint [9]. In many recent studies the movement of the temporomandibular joint has been imaged directly using MRI [10] [11] [12, 13], however, all of them examined only one side of the temporomandibular joint. However, the temporomandibular joint is the only bilaterally coupled joint in the human body. Thus, temporomandibular joint dysfunction on one side can have an effect on the joint on the other side, resulting in an influence on the movement of the mandibular head [4, 14,