Masticatory muscle activity during teeth clenching is affected by occlusal pattern. However, few studies have performed simultaneous evaluation of all masticatory activities during teeth clenching under various occlusal conditions. The aim of this study was to use muscle functional magnetic resonance imaging (mfMRI) to evaluate the effects of changes in occlusal point on masticatory activity during single tooth clenching. Changes in mean proton transverse relaxation time (∆T2) as an index of activity in all masticatory muscles during left unilateral clenching at the first molar or first premolar for 1 min were examined in nine healthy volunteers. Bite force was maintained at 40% of the maximum voluntary clenching force. The ∆T2 values of the masseter and lateral pterygoid muscles were analysed separately for superficial and deep layers, and for superior and inferior heads. The ∆T2 values for the ipsilateral deep masseter were significantly lower, and for the superior head of the ipsilateral lateral pterygoid muscles were significantly higher, after left first premolar clenching compared to left first molar clenching. These results quantitatively demonstrate a significant increase in activity of the superior head of the ipsilateral lateral pterygoid muscle and a significant decrease in activity of the ipsilateral deep masseter muscle with forward displacement of the occlusal contact point during unilateral tooth clenching.

Purpose: The purpose of this study was to determine the effect of number of chewing strokes on change in blood flow in denture-supporting maxillary mucosa.Methods: Subjects consisted of 11 healthy dentate men. Mastication was simulated by intermittent loading (10 N, 1/0.75 Hz) on a lateral area of the hard palate using a 2-cm 2 test plate.Loading duration was set at 1, 4, 8 or 12 minutes (80, 320, 640 or 960 chewing strokes). A non-contact laser Doppler blood flow meter was used to determine change in blood flow and time taken for recovery to 110% of the pre-loading value. Mean blood flow at pre-loading and at each duration of intermittent loading were compared using a repeated measures ANOVA (α =0.05) and the Dunnett test. Recovery times for each loading duration were compared using a one-way ANOVA (α=0.05) and the Bonferroni test.Results: Three subjects showed no increase in mean blood flow with loading. Eight subjects consistently showed an increase in mean blood flow during intermittent loading relative to at pre-loading. Duration of loading yielded no significant difference in mean blood flow.Significant differences were observed in recovery time between at after 8 min loading and at after the other 3 loading (1 min, 4 min, and 12 min loading) durations.Conclusion: Number of simulated chewing strokes showed no influence on mean blood flow during intermittent loading in denture-supporting mucosa. It did, however, affect 3 recovery time taken for blood flow to return to its pre-loading level.

SummaryIn a previous study, we used muscle functional magnetic resonance imaging to show that the anterior movement of the occlusal point increased the activity of the superior head of the ipsilateral lateral pterygoid muscle (ipsilateral SHLP) during unilateral single-tooth clenching. The purpose of this study was to verify the hypothesis that the increased activity of the ipsilateral SHLP described above serves to antagonise the occlusal force acting on the condyle. In total, 9 healthy volunteers were requested to perform left unilateral clenching at the first molar or first premolar region for 1 minute at 20% or 40% maximum voluntary clenching force. Changes in the mean proton transverse relaxation time (∆T2) were examined from the magnetic resonance images obtained before and after each clenching act as an index of the activity in all masticatory muscles. Correlation analyses of the mean ΔT2 for each volume of interest were performed with the first molar or premolar clenches to analyse the correlation between the activities in each muscle. A statistically significant correlation was exhibited between the ipsilateral temporal and ipsilateral SHLP (r = .651, P = .003) during first premolar clenching. However, no significant correlations were observed in the ipsilateral SHLP during first molar clenching. The results of this study suggest that the ipsilateral SHLP may contribute to the pulling of the mandibular condyle forward against the occlusal force generated by the ipsilateral temporal muscle. K E Y W O R D Sactivity, clenching, magnetic resonance imaging, masticatory muscle, occlusal, quantification