Purpose: The aim of this study was to clarify the characteristics of masseter muscle fatigue induced by experimental sustained light clenching with rest intervals between clenching events.
Materials and Methods: The subjects consisted of 18 healthy young adults. For each recorded task, the subjects were asked to perform experimental tooth clenching 3 times, with a duration of 60s for each event and an interval (30s or 60s) between successive clenching events. The experimental clenching forces selected were 10% and 20% of maximum voluntary clenching (MVC). The electromyographic activity during the experimental procedure was measured. The mean power frequency (MPF) of muscle activity was used as an indicator of muscle fatigue. Changes to lower frequencies of the MPF were then analyzed.
Results: Despite the light clenching forces used (10% and 20% of MVC), masseter muscle fatigue occurred. When the subjects performed experimental clenching at 10% of MVC with intervals of 60s between clenching events, the MPF changes were gradually larger depending on the events. The regression line had the best fit to data when the subjects were asked to perform experimental clenching under the conditions mentioned above.
Conclusion: It was possible to obtain a regression line that represented the relationship between clenching events and masseter muscle fatigue.