Athena Vale
Masseter muscle hypertrophy is a rare condition characterised by the enlargement of one or both masseter muscles, resulting in a square-angled face. The condition was first described in 1880 by an English physician, JW Legg, who reported the case of a 10-year-old girl with unilateral hypertrophy of the masseter and temporalis muscles. Masseter muscle hypertrophy can occur in anyone regardless of age, gender, or ethnicity, although people of Asian descent are more frequently affected. The true cause of this condition is typically unknown, but it is often associated with emotional stress, chronic clenching or grinding, gum chewing, and other factors that may overwork the masseter muscles. Treatment options range from conservative therapies such as behaviour therapy and botulinum toxin injections, to surgical procedures like liposuction or partial removal of the masseter muscle.
| Characteristics | Values |
|---|---|
| Cause | Unknown, but may be due to overworking the masseter muscles through emotional stress, chronic clenching/grinding, gum chewing, or defective teeth. |
| Diagnosis | Imaging modalities such as conventional radiography, computed tomography, and magnetic resonance imaging scans. |
| Treatment | Conservative/non-surgical therapies, including splint therapy, behaviour therapy, and botulinum toxin type A (Botox) injection therapy. Surgical treatments include the removal of part of the masseter muscle and jawbone or liposuction. |
| Symptoms | Limitations on mouth opening, swollen cheek, tension in the region of the hypertrophied muscle, pain, and functional disorders of the jaw. |
| Appearance | Square-angled face, creating a more masculine look in female patients or a bottom-heavy appearance. Unilateral hypertrophy can cause jaw asymmetry. |
| Age | Typically observed in adults aged 20-40, but cases have been documented in 10-year-olds. |
| Gender | No gender predominance, but a review of 108 cases found 57% were male. |
| Ethnicity | People of Asian descent are more frequently affected. |
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What You'll Learn
Causes
Masseter muscle hypertrophy is a rare condition characterised by unilateral or bilateral enlargement of the masseter muscles. It affects both males and females, typically in adulthood, and can cause psychological distress due to the change in facial appearance. Although the exact cause of this condition is unknown, there are several factors that have been associated with its onset.
The masseter muscle is essential for adequate mastication (chewing). Like other muscles in the body, the masseter muscle can enlarge or bulk up due to being overworked. Some common factors that can contribute to overworking the masseter muscles include emotional stress and chronic clenching or grinding, either during the day or while sleeping. Repetitive habits such as gum chewing or simply a preference for chewing on one side can also lead to masseter muscle hypertrophy.
People with psychological disorders or emotional disturbances that impact proprioception and the ability to keep the tone of the masseter muscle are at a higher risk of developing this condition. Additionally, certain conditions such as defective teeth, dysfunctional mastication, teeth grinding, and temporomandibular joint (TMJ) disorders have been associated with masseter muscle hypertrophy.
In some cases, the enlargement of the masseter muscle may be related to congenital factors. For example, a case report described a female patient in her 20s with masseter muscle hypertrophy and hemifacial hyperplasia, a developmental anomaly present since birth.
It is important to note that while these factors have been associated with masseter muscle hypertrophy, they have not been conclusively proven as the cause. The condition's aetiology remains largely unknown, and further research is needed to fully understand its underlying causes.
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Diagnosis
Masseter muscle hypertrophy is a rare condition that can be caused by overworking the masseter muscles through habits such as gum chewing, teeth grinding, or clenching. It is important to correctly diagnose this condition as it can be mistaken for other diseases, including masseter tumors, salivary gland disorders, muscle myopathy, and parotid inflammatory disease.
One diagnostic test involves palpating the muscle with the fingers while the patient clenches their teeth to make the muscle more prominent. With the muscle relaxed and the patient's mouth slightly open, extraoral palpation with both hands will help pinpoint the intramuscular location of the hypertrophy. Irregularities in the jaw angle may appear as a bone increase on an X-ray image.
According to Seltzer and Wang (1987), CT and MRI scans produce excellent images for the diagnosis of various masseter muscle conditions. However, Maxwell and Weggoner (1951) state that neurologic tests and electromyograms are not useful in diagnosing this condition.
Healthcare providers must understand the subtleties of masseter hypertrophy, as early detection and effective treatment can greatly enhance patients' quality of life.
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Symptoms
Masseter muscle hypertrophy is a rare condition that can occur unilaterally or bilaterally. It is characterised by an increase in the volume of the muscle mass, resulting in a square-angled face. This can create a more masculine look in female patients, or a bottom-heavy appearance, and in unilateral cases, it can cause jaw asymmetry.
While the condition is typically asymptomatic, some patients do experience pain. The most common complaints are related to cosmetic concerns, such as the exaggerated appearance of the muscle in the face, which can cause psychological distress.
Masseter muscle hypertrophy can also be associated with functional disorders of the jaw, such as trismus, protrusion, and bruxism. Patients may experience difficulty opening their mouths or temporomandibular symptoms. Bone spurs in the mandibular angle are also frequently observed.
The condition is often idiopathic, with no clear cause identified. However, certain factors have been associated with masseter muscle hypertrophy, including:
- Gum chewing
- Psychological disorders
- Emotional stress
- Chronic clenching or grinding, either during the day or while sleeping
- Repetitive habits, such as unilateral chewing
- Defective teeth
- Malocclusion
- Temporomandibular joint disorders
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Treatment
Masseter muscle hypertrophy refers to the enlargement of the masseter muscle, which often occurs in adults aged 20-40 and can affect both sides of the face. While the condition is not life-threatening, it can cause psychological distress due to the change in facial appearance, such as a square-angled jaw or asymmetry. Treatment options can be conservative/non-surgical or surgical, depending on the patient's preferences and the severity of the condition.
Conservative/Non-Surgical Treatment Options:
- Splint Therapy: This involves using an oral appliance, such as a mouthguard, to help reduce the force of clenching and grinding, which can contribute to the overworking of the masseter muscles.
- Behavior Therapy: Addressing behavioral habits that may be causing the overworking of the masseter muscles, such as gum chewing or emotional stress. Techniques for relaxation, stress management, thermal therapy, sleep hygiene, and dietary counseling may be taught.
- Botulinum Toxin Type A (Botox) Injection Therapy: This non-invasive method involves injecting the toxin into the hypertrophied muscle to reduce muscle contractions and volume. However, the effects are temporary, lasting about 6 months, and multiple injections are often needed.
Surgical Treatment Options:
- Surgical Debulking: This involves surgically removing part of the masseter muscle to reduce its volume. This method is considered the traditional approach but is more invasive than botulinum toxin injections.
- Liposuction: This procedure involves removing the fat near the masseter muscle to reduce the overall volume of the area.
- Radiofrequency Coagulation: A less invasive procedure introduced by Powell et al., which uses radiofrequency energy to create a safer and more long-lasting result compared to botulinum toxin therapy.
It is important to consult with a medical professional, such as a dentist, orofacial pain specialist, or oral surgeon, to determine the most appropriate treatment plan for masseter muscle hypertrophy.
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Case studies
Masseter muscle hypertrophy is a rare condition with unknown etiology, distinguished by either unilateral or bilateral enlargement of the masseter muscles. While it is often asymptomatic, it can be associated with pain, clenching, grinding, and functional disorders of the jaw. The condition can cause psychological distress due to the resulting square-angled or rectangular face, which can create a more masculine look in female patients.
Case 1: A 16-year-old Female with Unilateral Masseter Muscle Hypertrophy
A case report published in MDPI describes a rare instance of unilateral masseter muscle hypertrophy in a 16-year-old female, resulting in a gradual onset of painless swelling in the posterior left cheek and causing facial asymmetry. The diagnosis was suggested by clinical examination, ultrasound scanning, and nuclear magnetic resonance, and was confirmed by histologic examination two years later. The patient underwent surgical correction, with histological examination revealing skeletal muscle fibers associated with normal-sized muscle fibers.
Case 2: A Female in her 20s with Facial Asymmetry
A case report published in ScienceDirect describes a case of masseter muscle hypertrophy in a female patient in her 20s. The patient had a history of hemifacial hyperplasia from birth, which resulted in overgrowth of the right-side maxillofacial region. Following orthodontic treatment and osteotomy, the patient underwent debulking of the right masseter muscle. Histological examination revealed thick masseter muscle fibers arranged irregularly, with diameters ranging from 20 to 60 μm.
Case 3: A Study of 720 Subjects from Northeastern Germany
A study published in ScienceDirect investigated the relationship between masseter muscle hypertrophy and bruxism (teeth grinding) in 720 subjects from Northeastern Germany. The participants underwent whole-body MRI scans and oral examinations. The results indicated a higher prevalence of bruxism in women, but a larger cross-sectional area (CSA) of the masseter muscle in bruxing men. This study highlights the need for a gender-specific approach when evaluating the clinical implications of bruxism on the masseter muscle.
Case 4: A Series of Cases on Surgical Procedures
A series of case reports published by Venkatesh Anehosur, Anhad Mehra, and Niranjan Kumar in SAGE Journals focuses on the management of masseter muscle hypertrophy and the role of surgical procedures. The aim is to retrospectively analyze cases of masseter muscle hypertrophy and the surgical treatments employed. Various surgical approaches are discussed, including those proposed by Gurney, Adam, and Kim and Kameyama, involving muscle mass removal, mandibular angle osteotomy, and mandibular angloplasty, respectively.
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Frequently asked questions
Masseter muscle hypertrophy is a rare condition characterised by the unilateral or bilateral enlargement of the masseter muscles. It is often asymptomatic, but can be associated with pain, clenching/grinding, and functional disorders of the jaw.
The exact cause of masseter muscle hypertrophy is unknown, but it is believed to be idiopathic. Some common factors that can contribute to the condition include emotional stress, chronic clenching or grinding, repetitive habits such as gum chewing, and defective teeth.
There are both conservative and surgical treatments for masseter muscle hypertrophy. Conservative treatments include splint therapy, behaviour therapy, and botulinum toxin type A (Botox) injection therapy. Surgical treatments include partial removal of the masseter muscle and jawbone, or liposuction of the fat near the muscle.
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