Masticatory Muscle Atrophy

Masticatory muscle atrophy refers to the wasting or thinning of the muscles used for chewing — primarily the masseter, temporalis, medial pterygoid, and lateral pterygoid. In simple terms, these muscles lose size and strength over time, leading to a visibly sunken or asymmetrical appearance of the jaw and reduced bite force. Muscle atrophy generally occurs when muscle fibers shrink due to decreased use or loss of nerve supply; when this process affects the jaw-closing muscles, it’s called masticatory muscle atrophy Cleveland Clinic.

Anatomy of the Muscles of Mastication

Structure and Location

• Masseter: A thick, rectangular muscle on the side of the jaw, running from the cheekbone (zygomatic arch) down to the angle of the mandible Kenhub.

• Temporalis: A fan-shaped muscle on the side of the head, extending from the temporal fossa under the zygomatic arch to the coronoid process of the mandible Physiopedia.

• Medial Pterygoid: Located inside the mandible, attaching from the pterygoid plate of the sphenoid bone to the inner surface of the mandibular ramus Physiopedia.

• Lateral Pterygoid: A small, two-headed muscle deep to the other masticatory muscles, spanning from the sphenoid bone to the mandibular condyle and articular disc of the temporomandibular joint (TMJ) Physiopedia.

Origin and Insertion

• Masseter

  • Origin: Zygomatic arch

  • Insertion: Angle and lateral surface of mandibular ramus NCBI

• Temporalis

  • Origin: Temporal fossa and temporal lines of the skull

  • Insertion: Coronoid process and anterior border of the mandibular ramus Physiopedia

• Medial Pterygoid

  • Origin: Medial surface of lateral pterygoid plate and maxillary tuberosity

  • Insertion: Medial surface of mandibular angle

• Lateral Pterygoid

  • Origin: Greater wing of sphenoid (superior head) and lateral pterygoid plate (inferior head)

  • Insertion: Pterygoid fovea of the mandibular neck and TMJ disc

Blood Supply

• Primarily via the masseteric artery, a branch of the maxillary artery, with contributions from the facial artery NCBI.

• The temporalis receives blood from deep temporal branches of the maxillary artery and the middle temporal branches of the superficial temporal artery Physiopedia.

Nerve Supply

• All four muscles are innervated by the mandibular division (V₃) of the trigeminal nerve:

  • Masseteric nerve to the masseter

  • Deep temporal nerves to the temporalis

  • Medial and lateral pterygoid branches to the respective pterygoids NCBI.

Functions

The muscles of mastication work together to produce six primary movements of the jaw:

1. Elevation (closing the mouth)

2. Depression (opening the mouth)

3. Protrusion (jutting the jaw forward)

4. Retraction (pulling the jaw back)

5. Lateral deviation to the opposite side

6. Stabilization of the TMJ during speech and swallowing Physiopedia.

Types of Masticatory Muscle Atrophy

Muscle atrophy in the jaw can be classified by its underlying mechanism:

1. Neurogenic atrophy (due to nerve injury or disease)

2. Disuse atrophy (from prolonged immobilization, e.g., after jaw surgery)

3. Sarcopenic atrophy (age-related loss of muscle mass)

4. Cachexia (wasting from chronic illnesses like cancer)

5. Endocrine-related atrophy (from hormonal imbalances such as hypothyroidism)

6. Inflammatory myopathies (e.g., polymyositis)

7. Congenital myopathies (genetic muscle disorders)

8. Iatrogenic atrophy (e.g., from repeated botulinum toxin injections)

9. Traumatic atrophy (due to direct muscle or jaw injury)

10. Idiopathic atrophy (unknown cause) Cleveland Clinic.

Causes

Common factors that can lead to masticatory muscle atrophy include:

1. Trigeminal motor neuropathy (e.g., tumor compression) journalomp.org

2. Peripheral trigeminal nerve injury (e.g., facial trauma) journalomp.org

3. Prolonged jaw immobilization (e.g., after fracture repair) Cleveland Clinic

4. Age-related sarcopenia Wikipedia

5. Cancer cachexia Cleveland Clinic

6. Chronic malnutrition Cleveland Clinic

7. Hypothyroidism

8. Hyperthyroidism

9. Myasthenia gravis

10. Amyotrophic lateral sclerosis (ALS)

11. Muscular dystrophies

12. Polymyositis/dermatomyositis

13. Chronic infection (e.g., HIV)

14. Radiation therapy to head/neck

15. Stroke affecting trigeminal nucleus

16. Botulinum toxin overuse Frontiers

17. Statin-induced myopathy

18. Critical illness myopathy

19. Endocrine disorders (e.g., Cushing’s syndrome)

20. Idiopathic causes Cleveland Clinic.

Symptoms

Patients with masticatory muscle atrophy may experience:

1. Sunken cheek or facial asymmetry Cleveland Clinic

2. Difficulty chewing solid foods Cleveland Clinic

3. Reduced bite force Cleveland Clinic

4. Jaw fatigue on use Cleveland Clinic

5. Unilateral muscle wasting (in neurogenic cases) PMC

6. Jaw deviation when opening PMC

7. TMJ pain on use Cleveland Clinic

8. Ear ache (referred) Cleveland Clinic

9. Headaches Cleveland Clinic

10. Speech difficulties Cleveland Clinic

11. Drooling (in severe weakness) Cleveland Clinic

12. Muscle twitching or fasciculations Cleveland Clinic

13. Stiffness or tightness Cleveland Clinic

14. Jaw locking (in advanced cases) Cleveland Clinic

15. Weight loss from reduced intake Cleveland Clinic

16. Nutritional deficiencies Cleveland Clinic

17. Facial spasms (post-botox) Frontiers

18. Bruxism (compensatory patterns) Cleveland Clinic

19. Anxiety or stress about appearance Cleveland Clinic

20. Reduced quality of life Cleveland Clinic.

Diagnostic Tests

Evaluation may include:

1. Physical exam (inspection & palpation) Cleveland Clinic

2. Electromyography (EMG) NCBI

3. Nerve conduction studies NCBI

4. MRI of head/neck journalomp.org

5. Ultrasound of masseter muscle NCBI

6. CT scan of mandible NCBI

7. Muscle biopsy NCBI

8. Serum creatine kinase (CK) NCBI

9. Inflammatory markers (ESR/CRP) NCBI

10. Thyroid function tests NCBI

11. Nutritional panels Cleveland Clinic

12. Autoimmune serologies (ANA, anti-Mi-2) NCBI

13. Antibody tests for MG (AChR-Ab)

14. Genetic testing (for dystrophies)

15. Jaw opening measurement (millimeters) NCBI

16. Bite force dynamometry NCBI

17. Video fluoroscopy (for swallowing)

18. Endoscopy (to assess airway)

19. Bioelectrical impedance analysis

20. PET/SPECT (for tumor evaluation) journalomp.org.

Non-Pharmacological Treatments

Key non-drug interventions include:

1. Functional electrical stimulation Physiopedia

2. Resistive chewing exercises Physiopedia

3. Isometric jaw holds Physiopedia

4. Manual stretching of TMJ sarh

5. Ultrasound therapy Physiopedia

6. TENS (transcutaneous electrical nerve stimulation) Physiopedia

7. Myofascial release massage

8. Heat therapy (hot pack) PMC

9. Cold therapy (ice massage)

10. TMJ goldfish exercises sarh

11. Biofeedback for chewing patterns

12. Dietary modifications (soft, protein-rich) Cleveland Clinic

13. Speech therapy

14. Occupational therapy for jaw function

15. Acupuncture

16. Yoga/Tai Chi for stress reduction

17. Habit reversal training (for bruxism)

18. Postural correction exercises

19. Ergonomic advice

20. Dry needling

21. Laser therapy

22. Mirror therapy

23. Neuromuscular re-education

24. Chewing gum retraining

25. Soft diet progression

26. Nutritional counseling Cleveland Clinic

27. Facial splint therapy

28. Dental appliance adjustment

29. Stress management techniques

30. Regular follow-up and exercise progression Physiopedia.

Drugs

Pharmacologic options target underlying causes or support muscle mass:

1. Prednisone (inflammatory myopathies) NCBI

2. Methotrexate (polymyositis) NCBI

3. Azathioprine (autoimmune myositis) NCBI

4. Mycophenolate mofetil NCBI

5. IVIG (intravenous immunoglobulin) NCBI

6. Rituximab NCBI

7. Pyridostigmine (myasthenia gravis)

8. Megestrol acetate (appetite stimulant in cachexia) WebMD

9. Thalidomide (anti-cachexia) WebMD

10. Anamorelin (ghrelin receptor agonist)

11. Omega-3 fatty acids WebMD

12. Branched-chain amino acids WebMD

13. Creatine supplementation

14. Vitamin D WebMD

15. Calcium

16. Growth hormone

17. Testosterone or SARMs

18. Beta-hydroxy-beta-methylbutyrate (HMB)

19. NSAIDs (symptom relief)

20. Statins cessation (if statin-induced) WebMD.

Surgeries

1. Tumor resection & trigeminal nerve decompression for neurogenic atrophy journalomp.org

2. Trigeminal nerve graft or repair after trauma journalomp.org

3. Temporalis tendon transfer for masticatory reanimation PMC

4. Temporalis muscle flap with fascia lata graft Houston Methodist Leading Medicine

5. TMJ arthroplasty (disc repositioning/repair) Verywell Health

6. Total TMJ replacement in severe joint destruction Verywell Health

7. Mandibular osteotomy for malocclusion-related disuse PMC

8. Coronoidectomy to improve jaw opening SAGE Journals

9. Arthroscopic TMJ surgery for joint pathology Verywell Health

10. Gap arthroplasty for TMJ ankylosis Verywell Health.

Prevention Strategies

1. Regular chewing exercises Physiopedia

2. Balanced, protein-rich diet Cleveland Clinic

3. Early mobilization after jaw surgery Cleveland Clinic

4. Treat TMJ disorders promptly Verywell Health

5. Control chronic diseases (diabetes, HIV) Wikipedia

6. Vitamin D & calcium supplementation WebMD

7. Avoid unnecessary botulinum injections Frontiers

8. Maintain good dental health

9. Manage stress to reduce bruxism

10. Regular dental/medical check-ups Cleveland Clinic.

When to See a Doctor

Seek professional help if you experience:

• Persistent difficulty chewing or swallowing

• Noticeable facial asymmetry or sunken cheeks

• Jaw pain that limits movement

• Unexplained weight loss or malnutrition

• New onset of muscle weakness in the jaw Cleveland Clinic.

Frequently Asked Questions

1. What is masticatory muscle atrophy?
   It’s the gradual shrinking of the chewing muscles, leading to reduced jaw strength and a sunken appearance Cleveland Clinic.

2. What causes this condition?
   Causes range from nerve damage (e.g., trigeminal neuropathy) to disuse after immobilization, aging, cachexia, and more journalomp.orgCleveland Clinic.

3. How is it diagnosed?
   Diagnosis involves a physical exam, EMG, imaging (MRI/CT), blood tests (CK, thyroid), and sometimes muscle biopsy NCBI.

4. Can atrophy be reversed?
   Early stages (especially disuse atrophy) often improve with exercise and nutrition, but long-standing neurogenic atrophy may be permanent Cleveland Clinic.

5. What exercises help?
   Simple jaw opening/closing, resistive chewing with soft foods, and TMJ goldfish exercises can strengthen muscles sarh.

6. Are there medications for this?
   Drugs like megestrol (for cachexia), corticosteroids (for myositis), and pyridostigmine (for MG) can help address underlying causes WebMD.

7. When is surgery needed?
   Surgery is considered for nerve repair, TMJ ankylosis release, or muscle transfers (e.g., temporalis tendon transfer) if function doesn’t improve with conservative care PMC.

8. Is massage helpful?
   Yes—myofascial release and ischaemic compression can reduce tension and improve blood flow to atrophied muscles Physiopedia.

9. Can diet prevent atrophy?
   A protein-rich diet with sufficient calories, vitamins (D, C), and minerals (calcium) supports muscle maintenance Cleveland Clinic.

10. Does age always cause atrophy?
    Aging contributes (sarcopenia), but active exercise and good nutrition can slow or partially prevent muscle loss Wikipedia.

11. What role does nerve health play?
    Healthy trigeminal nerve function is critical; damage leads quickly to neurogenic atrophy of chewing muscles journalomp.org.

12. Are supplements useful?
    Supplements like HMB, creatine, branched-chain amino acids, and omega-3s may support muscle mass WebMD.

13. Can botulinum toxin cause atrophy?
    Yes—repeated BoNT injections into the masseter can weaken and shrink the muscle over time Frontiers.

14. How long does recovery take?
    With targeted therapy, mild cases may improve in weeks; severe or neurogenic cases may take months or need surgery Cleveland Clinic.

15. When should I see a specialist?
    If symptoms persist beyond two weeks despite home care, or if you have sudden muscle loss or jaw asymmetry, consult an oral maxillofacial surgeon or neurologist Cleveland Clinic.

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The article is written by Team Rxharun and reviewed by the Rx Editorial Board Members

Last Updated: April 24, 2025.

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