The masseter muscle is the primary muscle responsible for elevating the lower jaw and is the main muscle used for chewing. Located on the side of the face, it extends from the cheekbone down to the angle of the jawbone. When this muscle enlarges (masseter hypertrophy), it alters the facial contour, often resulting in a wider or more square-shaped lower face. While generally not harmful, enlargement can indicate underlying functional habits that may affect jaw health or cause discomfort.
Step-by-Step Self-Assessment
A simple physical examination can help determine if the masseter muscle is noticeably enlarged. The first step involves a visual inspection of the face, looking for asymmetry or noticeable bulging on one or both sides of the jaw near the back angle of the mandible. Enlargement often creates a prominent, square appearance in the lower third of the face.
The second step is palpation, or feeling the muscle with the fingers. Place your index and middle fingers on the side of your face over the angle of your jaw, just below the ear. Clench your teeth firmly together, then relax them, repeating this action while feeling the muscle contract and bulge.
A muscle that feels particularly firm or thick when clenched suggests enlargement. Comparing the size and prominence of the muscle on both sides is important, as hypertrophy can affect one side more than the other. This simple clench-and-feel method confirms the presence of muscle bulk.
Related Symptoms That Indicate Enlargement
An enlarged masseter muscle is often accompanied by functional symptoms. One common issue is jaw fatigue, where the muscles feel tired or strained after speaking, chewing, or at the end of the day. Pain or tenderness in the jaw area may also occur due to the muscle being overworked.
The excessive force and tension causing the enlargement often contribute to tension-type headaches. The constant strain can also affect the nearby temporomandibular joint (TMJ). This may lead to issues like clicking or popping sounds when opening and closing the mouth, or a jaw that feels temporarily locked or limited in its range of motion.
Common Causes of Masseter Hypertrophy
The primary reason the masseter muscle enlarges is overactivity. The most frequent behavioral cause is bruxism, which involves the habitual grinding or clenching of the teeth, often occurring unconsciously during sleep or periods of stress. This constant, forceful contraction leads to muscle tissue growth.
Excessive gum chewing is another common contributing factor due to the repetitive and prolonged use of the muscle. Emotional stress and anxiety play a role, often triggering subconscious clenching habits throughout the day. Unilateral hypertrophy, where only one side is enlarged, can be linked to a habitual preference for chewing food on that side of the mouth.
When to Seek Professional Advice
While masseter hypertrophy is generally a benign condition, consulting a healthcare professional is advisable if the enlargement causes pain, functional impairment, or significant cosmetic concern. A dentist or an orofacial pain specialist can perform a clinical examination to confirm the diagnosis. They will also rule out other potential causes of facial swelling, such as issues with the parotid gland.
Professional management often begins with conservative therapies, such as using a custom-fitted nightguard or splint to protect the teeth and jaw joint from nocturnal grinding forces. Behavioral and physical therapy techniques may also be recommended to increase awareness of daytime clenching and reduce muscle tension. For cases where conservative methods are insufficient, an effective treatment is the injection of a muscle relaxant, such as botulinum toxin, directly into the masseter. This causes the muscle to relax and gradually shrink, reducing both muscle size and associated pain symptoms.