Functional Characteristics of Orbicularis Oris and Buccinator Muscles during Mastication

Objectives: This study aimed to clarify the characteristics of orbicularis oris and buccinator muscle activities during mastication. Methods: Ten healthy males (26.9±1.0 yrs) with normal dentition participated. The electromyographic activities (EMGs) of their orbicularis oris and buccinator muscles during mastication were recorded using intramuscular fine-wire electrodes. The EMGs of their masseter and digastric muscles were also recorded using surface electrodes. The participants chewed various amounts of chewing gum (1 to 4 sticks) and peanuts (1 to 5 pieces) at an arbitrary chewing frequency on a unilateral side. The onset, offset, and duration of the orbicularis oris, buccinator, and digastric EMG bursts for each chewing cycle were normalized based on the masseter bursts. Results: The orbicularis oris and buccinator EMGs showed rhythmic single-peaked bursts corresponding to the jaw-opening phase of each chewing cycle for both food products. The chewing frequency did not depend on the amount chewed. The burst durations for both muscles increased significantly with the amount of gum (P<0.05, Friedman ANOVA) whereas the durations did not change with the number of peanuts. The burst onsets for both muscles did not change when the amount chewed was changed. The integrated EMGs for the orbicularis oris muscle were significantly increased when the amounts of both products were increased (P<0.05) while those for the buccinator muscle increased with the amount of gum (P<0.05); the change was not significant when the number of peanuts was changed. Conclusion: The activity of the orbicularis oris muscle depended on the amount of food product in the oral cavity, while that of the buccinator muscle depended on the amount of food product transferred onto the occlusal surface of the dental arch during mastication.