Near-infrared spectroscopy (LAIRS) is a noninvasive and simple technique for continuous measurement of tissue oxygenation of the brain and skeletal muscles. In this review paper, theoretical background of NIRS and difficulties to be overcome for practical applications are described. The presence of overlying tissues such as the skull and subcutaneous fat layer above the target tissues greatly affects the measurement sensitivity of NIRS. This is one of the most important factors to quantitatively determine the tissue oxygenation. We have investigated the influence of a fat layer on muscle oxygenation measurement and suggested a method for correcting this influence. Typical applications of our correction method are presented: 1) significant difference in reoxygenation rate immediately after exercise between top athletes and normal young adults, and significant increase in reoxygenation rate due to high-altitude training in top athletes; 2) estimation of local and instantaneous oxygen consumption during exercise; and 3) functional imaging of muscle oxygenation for spatio-temporal analyses of muscle metabolism and heterogeneity of muscle function. Despite great effects of many factors on measurements, only NIRS gives us a simple, noninvasive and continuous monitoring technique of tissue oxygenation. Results of our studies suggest that NIRS using an appropriate correction method is quantitative within acceptable accuracy and useful for physiological studies and clinical applications.

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We introduce a new method of four-dimensional display of mandibular movement using the 3D-CT images of the skull and mandible, the dental surface image using a non-contact 3-D laser scanner and the mandibular movement data using a six-degree-of freedom-jaw movement analyzer. This method was employed to perform dynamic and precise simulation of the mandibular function for a patient with jaw deformity.
The advantages of this system were as follows:
1. The lento-skeletal 3D image and the mandibular movement data were integrated on the same coordinates on a personal computer. The mandibular movement of multiple required points on the integrated images was displayed by the computer graphics, which make it possible clearly to grasp a relationship between the motion pattern of the mandibular movement, skeletal morphology and occlusion simultaneously.
2. This new method of analyzing the occlusal contacts and the condyle-fossa distance provides the comprehensive insight of the stomatognathic system not only at intercuspal position, but also at any mandibular positions during functional movement.
3. Our system to evaluate the intersection between morphology and function will certainly improve our understanding of the function of the temporpmandibular joint and occlusion. We believe that it is useful for diagnosing the temporomandibular disorders to patients with jaw deformities.

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This study examined the functional change in the auditory pathway caused by a change of mandibular position. This was measured in closed position (CP) and canine apical position (lateral position, LP) and incisor position (PP) between maxilla-mandibular relation in a healthy subject. Tympanometry was used to assess sound conduction function, distortion product otoacoustic emission (DPOAE) for cochlear nerve function, and auditory stapedius reflex (SR) for brainstem response.
1. In SR, a change was not noted in the reflex threshold. Significant difference in delay of onset latency L₁ was recognized in working side (WS) and in non-working side (NW), but it was not recognized in PP.
2. From tympanogram, WS and NW and PP protrusive position showed significant increase in STC, but no difference was noted in middle ear pressure (PRS) or middle ear clearance (EAC) .
3. DP level showed significant decrease at 2000 Hz and increase at 5031 Hz in WS. On the other hand, it showed a significant increase at 1250 Hz and 5031 Hz, and decrease at 2000 Hz in NW, but it was not recognized in PP. From these results, it is thought that mandibular position alters action of outer cochlear hair cells and tympanic muscle of middle ear transmission system, and also, these possible relationships would be recognized as the responses in stapedius reflexes throughout brainstem. These changes are reversible, therefore, the possibility of numerical analysis of physiological mandibular position is suggested by auditory stapedius reflex.

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Stomatognathic function is developed in steps from the latter half of infancy up to childhood. This period is thought to be critical for stomatognathic function acquisition. In this study, we investigated how the consistency of the daily diet after weaning affects the development of stomatognathic function in mice. C3H mice were divided into liquid- and solid-diet group. Three-dimensional jaw-movement tracking and jaw-muscle electromyography (EMG) were recorded simultaneously during chewing of pellet and bread at 11 weeks of age. As a result, we found that (1) The masseter activity was larger in the liquid-diet group than the solid-diet group. (2) Total cycle duration indicating chewing rhythm and gape size indicating burst pattern were significantly longer and larger during pellet chewing than bread chewing in the solid-diet group. On the other hand, there was no significant difference in both parameters in the liquid-diet group. These results suggest that greater EMG bursts are necessary, since the masticatory muscles are weaker in mice fed with liquid diet, and that the capacity to perceive the consistency of diet is reduced in these mice. The development of the mechanism to regulate chewing rhythm and pattern is considered to be impeded when raised on soft diet.

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