Digastric Muscle Function in Mastication
Primary Function
The digastric muscle functions primarily as a jaw opener during mastication, initiating the open-close chewing cycle by depressing the mandible, and secondarily stabilizes the temporomandibular joint during the closing phase through a second burst of activity. 1
Biomechanical Role During the Chewing Cycle
Jaw Opening Phase
- The digastric muscle initiates the open-close chewing cycle by actively contracting to depress (open) the mandible 1
- This opening action precedes the activation of the elevator muscles (temporalis and masseter) that close the jaw 1
- During this phase, the digastric generates substantial positive work to overcome the resistance of jaw closure 2
Jaw Closing Phase (Stabilization Function)
- A second burst of digastric activity occurs during the closing phase of mastication, analogous to the human lateral pterygoid muscle 1
- This secondary activation stabilizes the structures of the temporomandibular joint and mandibular condyle during jaw closure 1
- During this phase, the digastric absorbs negative work (lengthens under tension), producing on average a relatively small amount of net negative work across the complete chewing cycle 2
Functional Partitioning and Neural Control
- The digastric muscle contains two to three functional subregions innervated by separate branches of the mylohyoid nerve, allowing differential activation patterns during mastication 3
- Electromyographic activity varies between recording sites within the muscle during the masticatory cycle, with the caudal region sometimes activating before the anterior region when the jaw swings laterally 3
- Despite functional partitioning, motor neurons controlling these regions are intermingled within the trigeminal motor nucleus, suggesting integrated motor command distribution 3
Relative Contribution to Mandibular Loading
- The digastric muscle plays only a small role in the continuous loading of the mandible compared to the masseter muscle 4
- The masseter muscle loads the mandible almost continuously throughout the day with thousands of isolated bursts, whereas mandibular strain events rarely occur without simultaneous masseter activity 4
- The digastric's primary mechanical contribution is during the active jaw-opening phase rather than sustained mandibular loading 4
Clinical Relevance to Swallowing
- While the digastric is anatomically classified as a muscle of mastication, it also participates in the oral preparatory phase of swallowing by working with the tongue, lips, and mandible to masticate food and mix it with saliva 5
- Weakness of oral-phase muscles including the digastric can contribute to dysphagia with both anterior saliva loss (drooling) and posterior aspiration risk 6