From the Guidelines
To examine for weakness of the masseter muscle, ask the patient to clench their teeth while you palpate both masseter muscles simultaneously with your index and middle fingers placed over the angle of the jaw, as this method allows for direct assessment of muscle strength and bulk 1. When performing this examination, it is essential to compare the strength and bulk of contraction on both sides to identify any asymmetry, atrophy, or reduced strength.
- The patient should be instructed to clench their teeth tightly, allowing for optimal engagement of the masseter muscles.
- The examiner should use their index and middle fingers to palpate the masseter muscles, feeling for the contraction and strength of the muscles.
- The examination can also include asking the patient to bite down on a tongue depressor or the examiner's gloved fingers while attempting to pull it out, assessing resistance 1. This approach is supported by a study published in Sports Medicine in 2023, which found that clenching the masseter muscles tightly resulted in statistically significant decreases in head acceleration and increases in masseter and sternocleidomastoid muscle activity 1. Additionally, a systematic review published in the British Journal of Sports Medicine in 2020 emphasizes the importance of undertaking a physical examination, including assessment of mobility and/or muscle strength, in the evaluation of musculoskeletal pain 1. However, the most recent and highest-quality study 1 provides the most relevant guidance for examining masseter muscle weakness, and its findings should be prioritized in clinical practice.
From the Research
Examination Methods for Masseter Muscle Weakness
To examine for weakness of the masseter muscle, several methods can be employed, including:
- Electromyographic (EMG) examination, which can provide useful information on the muscular profile and evaluate therapeutics 2
- Ultrasound imaging, which can quantify muscular deformation patterns in the masseter muscle and provide a repeatable and sensitive tool for functional analysis of the masticatory organ 3, 4
- Analysis of muscle deformation patterns using software, which can highlight the distinct activity of each separate part of the muscle 4
- Electrophysiological studies, which can confirm masticatory muscle weakness and suggest the cause of the weakness 5
- Evaluation of the tone and viscoelastic properties of the masseter muscle, which can reveal its relationship with age and gender 6
Diagnostic Tools
The following diagnostic tools can be used to examine the masseter muscle:
- Electromyography (EMG) machine
- Ultrasound machine with a linear probe
- Software for analysis of muscle deformation patterns
- Devices for evaluating the tone and viscoelastic properties of the masseter muscle
Considerations
When examining the masseter muscle, it is essential to consider the following: