What causes trismus? Symptoms, diagnosis, treatment, and exercises for trismus

Trismus is the medical term for “lock-jaw,” a condition that causes the muscles in the jaw, known as the muscles of mastication, to spasm or contract uncontrollably. Trismus lockjaw is commonly associated as an effect of tetanus infection but can be the result of a few causes. Those affected by trismus typically have an inability to open their mouth, making it difficult to eat, perform speech, and maintain proper oral hygiene.

There are temporary and permanent cases of trismus development, however, most cases tend to fall into the former. The normal variation of mouth opening falls in the range of 40 to 60mm, which is akin to about two fingers’ breadth up to three fingers’ breadth with some variation found between genders.

Trismus grading may be referred to as the distance between the front upper and lower teeth (incisors) when the mouth is fully open:

  • Mild: >30 mm
  • Moderate: 15-30 mm
  • Severe: <15 mm

A more precise trismus definition would be difficulty opening the mouth due to muscle spasm from a disturbance in the trigeminal nerve. While this cranial nerve is responsible for various other facial functions, its disturbance simply causes limited mouth opening in cases of trismus.

What causes trismus?

The muscles of mastication consist of the temporalis, masseter, medial pterygoid, and lateral pterygoid, with each playing an important role, allowing us to chew our food. Damage to any one of these muscles can cause limitations in mouth opening and the inability to chew due to pain. This pain reflex is often referred to as “muscle guarding” and develops when the muscle fibers provoke pain when they are stretched. Pain causes muscles to contract, resulting in a decrease in range of motion that is uncontrollable by the patient.

Trismus causes include:

Infection: Maybe tooth related (odontogenic) or non-tooth related (non-odontogenic). Odontogenic infection can be pupal, periodontal, or pericoronal in origin, with oral infections around the third molar being the most common. Severe oral infections, if left untreated, often present with trismus that can lead to more complications such as cervical cellulitis or mediastinitis. Non-odontogenic infections include tonsillitis, tetanus, meningitis, parotid abscess, and brain abscess leading to the development of trismus.

Trauma: Fractures to the jaw bones can lead to limited jaw opening with the degree of limitation depending on the type of injury and the direction of the traumatic force. Trauma can be the result of a sports injury or even the result of a difficult dental procedure such as tooth extraction. Accidental injuries leading to external penetration of a foreign object may also cause trismus but is relatively rare.

Temporomandibular joint disorder: This disorder is characterized by excruciating pain or tenderness of your jaw. We use our jaw muscles every day to chew our food, to speak, and even simply just breathing through our mouths. All of these actions rests upon a joint called the temporomandibular joint. This sliding hinge can be the source of pain felt in the joint itself as well as the muscles that control jaw movement. The exact reasons for TMJ disorders to develop may be difficult to determine, but can be the result of several factors including genetics, arthritis, or jaw injury.

Drug therapy: Secondary effects of some drugs can lead to the development of trismus. Drugs may include succinylcholine, phenothiazines, and tricyclic antidepressants, and are considered some of the most common drug-related causes.

Radiotherapy/chemotherapy: Cells of the oral mucosa have a high growth rate and are susceptible to the toxic effects of chemotherapy, leading to the development of stomatitis; an inflamed or sore mouth. This condition can cause severe discomfort, pain, trismus, and difficulty swallowing. The use of radiotherapy may lead to the development of a condition called osteoradionecrosis; bone death due to radiation, which can result in pain, trismus, pus formation, and occasional foul-smelling wounds.

Tumors and oral malignancies: Primary or secondary neoplastic disease in the epipharyngeal region, parotid gland, jaws, or TMJ can lead to trismus. Fibrosis of submucosal tissue causes blanching of the mucosa and can affect speech by restricting the tongue and soft palate movements.

Congenital/developmental causes: Hypertrophy (increase in size) of the coronoid process causing interference of the coronoids against the anteromedial margin of the zygomatic arch occasionally report accompanying trismus. Trismus-pseudo-camptodactyly syndrome is a rare condition that may also be associated this trismus development.

Symptoms of trismus

Limitations with opening the mouth bring about a host of additional complications. You are able to chew food well, causing you to drastically change your diet, which may potentially lead to inadequate nutrition. The cause of your trismus will also bring with it additional presentations. The following are the most commonly observed trismus symptoms:

  • Fever (in infections)
  • Stiffness, severe or dull aching pain, tenderness or swelling in the chewing muscles
  • Grating, cracking, clicking or popping sounds during the movements of the lower jaw
  • Decreased range of motion in the temporomandibular joint (TMJ)
  • Decreased ability to chew, talk, sing, yawn, and brush teeth
  • Difficulty swallowing or choking
  • Deviation of the jaw toward the affected side
  • Earache, headache
  • Difficulty breathing

Diagnosis of trismus

A complete medical history will be taken to assess for any possible predisposing event that may have led to trismus development. Next, a physical exam will be done on the affected area as well as an examination of the teeth, bite, and alignment of the jaw joints. A measure of how much you can open your mouth will also be taken

Your doctor may feel the need to order imaging in the form of a CT or MRI. A tomography, a type of x-ray, may also be done to assess cross sections of the jaw area.

Treatment for trismus

Trismus treatment will depend on the underlying cause and usually needs to be implemented in a timely fashion before the condition worsens. Mild cases of pain and dysfunction can be managed with heat therapy, analgesics, muscle relaxants, and a soft diet if necessary until an examination can be scheduled. These are the most common initial trismus treatment guidelines.

Heat therapy consists of placing a moist hot towel on the affected area for about 15 to 20 minutes every hour. Medications such as aspirin and other anti-inflammatories can be helpful in cases of trismus. For intense pain and discomfort, the use of narcotic analgesics may be used at the discretion of the prescribing physician.

When the acute phase is over, patients are advised to initiate physiotherapy for opening and closing the jaws. Chewing sugarless gum is another way of providing lateral movement of the temporal mandibular joint. Cases of painful infected teeth should be taken care of by a dentist.

Prevention of trismus

Prevention will depend on the particular cause of trismus. For prevention due to tetanus, getting the tetanus vaccination with subsequent boosters every 10 years can help prevent the condition. Practicing safety during physical activity will help avoid injury to the jaw area.

In general, massaging and exercising the jaw muscles will help keep them in good working order and alert you when an abnormality is present. Is it also recommended to maintain good posture and oral hygiene as an additional preventive measure.

Exercises for trismus

The following are various jaw exercises that can be helpful in regaining full jaw function:

  • Jaw openings
    • Open your mouth as wide as possible, holding it open for seven seconds then releasing. Repeat seven times.
    • Open your mouth as wide as possible, then move your jaw to the left and release. Repeat five times.
    • Open your mouth as wide as possible then move your jaw to the right and release. Repeat five times.
  • Passive stretching
    • Place one thumb on your top front incisors while placing your index finger on the lower incisors.
    • Use your fingers to open your mouth and hold the stretch.
  • Springy bites
    • Place one thumb on your top front incisors while placing your index finger on the lower incisors.
    • Now gently practice springy bites using your jaw muscles. Be careful not to bite down too hard onto your fingers.
    • Perform this exercise for one minute many times throughout the day.

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Related Reading:

How does TMJ (temporomandibular joint) disorder cause tinnitus, hearing problems?

TMJ home treatment: Exercises and home remedies to treat TMJ

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