Trismus: Understanding Lockjaw, Its Causes, Symptoms, and Treatment

What's a trismus?

Trismus is a condition characterized by a limited ability to open the mouth, often due to spasm or inflammation of the muscles of mastication (jaw muscles) or temporomandibular joint (TMJ) dysfunction. It is commonly referred to as "lockjaw" when severe.

Understanding Trismus: A Core Definition

Trismus, derived from the Greek word "trismos" meaning a grinding or grating, refers to a sustained contraction or spasm of the jaw muscles, leading to a restricted range of motion when attempting to open the mouth. While often temporary, it can significantly impair essential functions such as eating, speaking, and maintaining oral hygiene. It's crucial to differentiate trismus from tetanus-induced lockjaw, which is a specific, severe form caused by the Clostridium tetani bacterium affecting the nervous system. Our focus here is on the broader, more common muscular and mechanical causes.

Anatomy and Physiology Behind Jaw Movement

To understand trismus, it's essential to grasp the mechanics of normal jaw movement. The jaw, or mandible, articulates with the skull at the temporomandibular joints (TMJs), located just in front of the ears. These are complex synovial joints that allow for a wide range of movements: elevation (closing), depression (opening), protraction (forward movement), retraction (backward movement), and lateral excursion (side-to-side movement).

The primary muscles responsible for jaw movement, collectively known as the muscles of mastication, include:

• Masseter: A powerful muscle, primarily responsible for jaw elevation (closing).
• Temporalis: Also involved in elevation and retraction of the jaw.
• Medial Pterygoid: Works with the masseter and temporalis for elevation and also aids in protraction and lateral movements.
• Lateral Pterygoid: The primary muscle for jaw depression (opening), protraction, and lateral movements.

These muscles are innervated by the trigeminal nerve (Cranial Nerve V). Any disruption to these muscles, their innervation, or the TMJ itself can lead to trismus.

Common Causes of Trismus

The causes of trismus are diverse, ranging from minor irritation to serious medical conditions. Identifying the underlying cause is paramount for effective treatment.

• Dental Procedures: This is the most common cause.
  • Wisdom Tooth Extraction: Especially lower wisdom teeth, due to trauma to the surrounding muscles (medial pterygoid, masseter), inflammation, or local anesthetic injection into the muscle.
  • Root Canal Treatment or Extensive Dental Work: Prolonged mouth opening can strain jaw muscles.
  • Infection from Dental Procedures: Post-extraction infection (e.g., dry socket) or abscesses can cause inflammation and muscle spasm.
• Infection:
  • Pericoronitis: Inflammation of the gum tissue around an erupting wisdom tooth.
  • Dental Abscesses: Infections originating from teeth that spread to surrounding tissues.
  • Tonsillitis or Peritonsillar Abscess (Quinsy): Inflammation or infection near the throat can affect jaw opening.
  • Parapharyngeal Space Infection: A serious deep neck infection.
  • Tetanus: A severe bacterial infection (often from puncture wounds) that causes widespread muscle spasms, including the jaw muscles ("lockjaw").
• Trauma:
  • Fractures of the Jawbone (Mandible): Can directly impede movement.
  • Direct Trauma to the Jaw Muscles or TMJ: Blows to the face can cause bruising, swelling, and muscle guarding.
• Temporomandibular Joint (TMJ) Disorders:
  • Disc Displacement: The articular disc within the TMJ can become displaced, blocking normal movement.
  • Arthritis: Osteoarthritis or rheumatoid arthritis affecting the TMJ can cause pain and restricted motion.
  • Ankylosis: Fusion of the joint, often due to trauma or infection, leading to complete immobility.
• Neurological Conditions:
  • Stroke: Can lead to muscle spasticity.
  • Dystonia: A movement disorder causing involuntary muscle contractions.
  • Multiple Sclerosis: Can affect muscle control.
  • Trigeminal Neuralgia: While primarily pain, severe cases might lead to muscle guarding.
• Radiation Therapy: For head and neck cancers, radiation can cause fibrosis (scarring and stiffening) of the jaw muscles and TMJ, leading to chronic trismus.
• Medication Side Effects: Certain medications, particularly some antipsychotics (e.g., phenothiazines) and antiemetics, can cause acute dystonic reactions leading to trismus.
• Tumors: Tumors in the parotid gland, pharynx, or oral cavity can physically obstruct jaw movement or infiltrate the muscles.

Recognizing the Symptoms

The primary symptom of trismus is a limited opening of the mouth. However, other accompanying symptoms can provide clues to the underlying cause:

• Difficulty chewing or swallowing.
• Pain in the jaw, face, or ear.
• Stiffness or tenderness in the jaw muscles.
• Headaches.
• Clicking or popping sounds in the jaw joint (TMJ disorders).
• Fever or swelling (if infection is present).
• Changes in speech.
• Difficulty with oral hygiene due to limited access.

The normal interincisal opening (distance between upper and lower front teeth) is typically 40-60 mm. Trismus is usually diagnosed when this opening is less than 35-40 mm, with severe cases being less than 20 mm.

Diagnosis and Assessment

Diagnosing trismus involves a thorough clinical examination and often imaging studies.

• Medical History: The healthcare provider will ask about recent dental procedures, trauma, infections, medications, and any pre-existing medical conditions.
• Physical Examination: This includes:
  • Measuring the maximum interincisal opening.
  • Palpating the jaw muscles (masseter, temporalis, pterygoids) for tenderness, spasm, or swelling.
  • Assessing the TMJ for pain, clicking, or crepitus.
  • Examining the oral cavity and throat for signs of infection, inflammation, or masses.
• Imaging Studies:
  • X-rays: To check for jaw fractures or bone abnormalities.
  • CT Scan (Computed Tomography): Provides detailed images of bone structures and can help identify infections or tumors.
  • MRI (Magnetic Resonance Imaging): Excellent for visualizing soft tissues like muscles, nerves, and the TMJ disc, useful for identifying muscle inflammation, fibrosis, or nerve involvement.

Treatment and Management Strategies

Treatment for trismus is highly dependent on the underlying cause. The goals are to alleviate pain, reduce inflammation, restore jaw mobility, and address the primary etiology.

• Addressing the Underlying Cause:
  • Antibiotics: If an infection (e.g., dental abscess, pericoronitis) is present.
  • Drainage of Abscesses: Surgical drainage may be required for pus collections.
  • Dental Interventions: Extraction of an infected wisdom tooth or other necessary dental treatments.
  • Cessation of Offending Medications: If drug-induced trismus is suspected.
• Pharmacological Management:
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): Ibuprofen, naproxen to reduce pain and inflammation.
  • Muscle Relaxants: Such as diazepam or cyclobenzaprine, to alleviate muscle spasm.
  • Corticosteroids: May be used in acute inflammatory cases to reduce swelling.
  • Botulinum Toxin (Botox) Injections: For chronic, severe muscle spasms, Botox can temporarily paralyze the overactive muscles, providing relief and allowing for physical therapy.
• Physical Therapy and Jaw Exercises: Crucial for restoring range of motion once acute pain and inflammation subside.
  • Passive Stretching: Gentle, sustained stretching of the jaw muscles.
  • Active Exercises: Opening and closing the mouth within the pain-free range, lateral movements.
  • Jaw Mobilization Devices: Tools like "TheraBite" or "Dynasplint" can be used to gradually increase mouth opening.
  • Heat Therapy: Applying warm compresses to the jaw can help relax muscles and increase blood flow.
• Dietary Modifications: A soft diet is recommended to minimize strain on the jaw muscles during the recovery phase.
• Surgical Intervention: Rarely needed for trismus itself, but may be necessary for:
  • Repairing jaw fractures.
  • Removing tumors or addressing structural abnormalities affecting the TMJ.
  • Releasing severe fibrous bands (e.g., post-radiation trismus, though other methods are preferred initially).

Prevention and Prognosis

Prevention of trismus often focuses on careful surgical technique during dental procedures, managing infections promptly, and early intervention for TMJ issues. For patients undergoing head and neck radiation, prophylactic physical therapy and jaw exercises are sometimes recommended.

The prognosis for trismus varies widely:

• Acute Trismus: From dental procedures or minor infections, typically resolves within a few days to weeks with appropriate treatment.
• Chronic Trismus: From radiation fibrosis, severe TMJ dysfunction, or neurological conditions, can be more challenging to manage and may require long-term physical therapy and ongoing medical management.

When to Seek Medical Attention

While many cases of trismus are mild and resolve on their own or with basic home care, it's important to seek medical attention if you experience:

• Sudden onset of severe inability to open your mouth.
• Trismus accompanied by fever, swelling, or redness.
• Difficulty swallowing or breathing.
• Persistent pain that doesn't improve with over-the-counter pain relievers.
• Trismus lasting longer than a few days.
• Any concerns about a recent dental procedure or injury.

Early diagnosis and treatment are key to preventing complications and ensuring a full recovery of jaw function.