Tsunehiko TAKEUCHI^* and Takehiro KURONO

Central Research Laboratory, Hamamatsu Photonics K.K., 5000 Hirakuchi, Hamakita, Shizuoka 434-8601, Japan

(Received February 17, 2003; Accepted May 16, 2003)

To non-invasively determine the condition of the masticatory muscles during chewing in real time, we used near-infrared spectroscopy and measured the masseter muscle. It increased in size, while the deoxy Hb in this muscle experienced the change in the short cycle by chewing. Periodic change of deoxy Hb was in agreement with the vertical movement of the lower jaw. It was found that the amount of increase in the deoxy Hb differs depending on the hardness of food being chewed. Moreover, by carrying out simultaneous measurement of the masseter muscles on both side of the jaw it was possible to determine the predominant muscles currently used in chewing.

Key words: near-infrared spectroscopy, oxygenation, mastication, chewing, masseter muscle, masticatory force

^*Correspondence author. E-mail address: take@crl.hpk.co.jp