Differences in mandibular movements and muscle activities between natural and guided chewing cycles

Area of Science:

• Biomechanics
• Neuroscience
• Physiology

Background:

• Chewing is a complex motor task involving coordinated mandibular movements and muscle activity.
• Understanding how chewing adapts to different food textures and pacing is crucial for masticatory function.
• Previous research has explored jaw muscle responses to various stimuli, but a comprehensive analysis under controlled conditions is needed.

Purpose of the Study:

• To investigate the effects of food physical properties and chewing rate on mandibular movements and associated muscle activities (masseteric and digastric).
• To determine the relationship between chewing rate and the duration of masseteric and digastric muscle bursts.
• To compare the variability of masseteric versus digastric muscle burst durations during voluntary alterations in chewing rate.

Main Methods:

• Electromyography was used to record muscle activities of the masseter and digastric muscles.
• Subjects performed chewing tasks with various food types (marshmallow, crisp bread, carrot, cheese, dried cuttlefish).
• Chewing rate was controlled using audio pacing signals and voluntary adjustments.

Main Results:

• Increased chewing rate led to shortened durations of both masseteric and digastric muscle bursts, irrespective of food type.
• The masseteric muscle burst duration showed a stronger correlation with chewing rate compared to the digastric muscle burst.
• Voluntary changes in chewing rate resulted in greater variation in the duration of the digastric muscle burst than the masseteric muscle burst.

Conclusions:

• Mandibular muscle activity patterns, specifically masseteric and digastric bursts, are significantly influenced by chewing rate.
• The masseter muscle appears more tightly regulated by chewing frequency, while the digastric muscle exhibits greater adaptability to voluntary rate changes.
• These findings provide insights into the neuromuscular control of mastication and its adaptability to varying demands.