Quantitative analysis of masticatory activity during unilateral mastication using muscle fMRI

OBJECTIVE: Quantitative analysis of the activities of all masticatory muscles is required to elucidate the mechanism of stomatognathic dysfunction. Electromyography can be used to record the activity of masticatory muscles, but quantification of the overall activity of every masticatory muscle has not been accomplished because of methodological limitations. In this study, we used muscle functional magnetic resonance imaging for simultaneous quantification of the overall activities of the masseter, medial pterygoid and lateral pterygoid muscles during unilateral gum chewing. METHODS: Seven healthy male volunteers participated in the study. We evaluated changes in the mean proton transverse relaxation time in the bilateral masseter, medial pterygoid and lateral pterygoid muscles before and after unilateral gum chewing, and to quantify the overall activity of these muscles simultaneously during unilateral gum chewing. RESULTS: After 5 min of chewing, the activity of the ipsilateral masseter was highest among the six muscles, followed by the ipsilateral medial pterygoid, contralateral lateral pterygoid and contralateral masseter muscles. CONCLUSION: These results affirm the importance of the ipsilateral masseter muscle and quantitatively demonstrate the important contribution of the ipsilateral medial pterygoid and contralateral lateral pterygoid muscles during unilateral mastication.