Trismus, or lockjaw, is a painful condition in which the jaws do not open fully. As well as causing pain, trismus can lead to problems with eating, speaking, and oral hygiene.

Trismus occurs when a person is unable to open their mouth more than 35 millimeters (mm). It can occur as a result of trauma to the jaw, oral surgery, infection, cancer, or radiation treatment for cancers of the head and throat.

Most cases of trismus are temporary, typically lasting for less than 2 weeks, but some may be permanent.

In this article, we explore the causes and symptoms of trismus. We also look at the current treatment options for this condition.

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Trauma and inflammation are possible causes of trismus.

There are many possible causes of trismus, including the following:

Trauma

Injury or damage to the jaw can lead to trismus. Examples of such trauma include fractured jawbones or tissue damage following dental surgery.

Others include:

Inflammation

Some medical conditions that cause inflammation in the mouth may cause trismus. One example is pericoronitis, which is inflammation of the soft tissue around a tooth, potentially leading to an impacted molar.

Others include:

  • arthritis in the jawbones
  • scleroderma, which is an autoimmune disease that affects connective tissue
  • soft tissue fibrosis, which occurs when excess fibrous connective tissue forms

Dental surgery

Oral surgery, including wisdom tooth extraction, may cause inflammation in the mouth, which can lead to trismus.

Hyperextension, which is having to open the mouth wider than its usual range of motion, during surgery may also lead to lockjaw.

Infection

Infections can contribute to trismus in some cases.

Types of infections that may do this include:

Cancer or cancer treatment

Cancerous tumors in the head or throat can affect the function of the jaw.

Radiation treatment for these tumors can also cause trismus.

According to a small 2016 study consisting of 30 participants with oral cancer, trismus affected 53.3% of them at the time of diagnosis.

This number increased to 86.7% after surgery and 85.7% after radiotherapy.

While anyone can develop trismus, some factors may increase the chance of developing it.

These include:

  • having head or neck cancer
  • undergoing radiation treatment for head or neck cancer
  • recent oral surgery to remove a wisdom tooth
  • recent trauma to the mouth or jaw
  • having certain types of mouth infection

The defining symptom of trismus is the jaw not opening fully or opening to 35 mm or less.

Other symptoms include:

  • jaw pain and cramping
  • difficulty biting, chewing, or brushing the teeth
  • inability to swallow some foods
  • headaches
  • earache

Typically, treating the underlying condition should resolve many cases of trismus.

Generally, the earlier a person seeks treatment, the better the outcome.

Treatment options include:

Medication

It may be necessary to take medication to reduce pain and relax the jaw muscles. Common medications for trismus include muscle relaxers and nonsteroidal anti-inflammatory drugs (NSAIDs) to relieve pain.

Depending on the severity of the symptoms, a doctor may prescribe oral medications or drugs that require injection into the jaw.

Some forms of NSAIDs are also available over the counter.

Jaw-stretching devices

A doctor or physical therapist may recommend the use of a jaw-stretching device.

In a 2014 study, people who used such a device when performing specific mouth exercises had an average increase in mouth opening of 5.5–7.2 mm.

Dietary changes

Individuals may need to make dietary changes until the condition improves.

For most people, moving to a soft foods diet is helpful because it is possible to eat these foods without opening the mouth too much.

Examples of soft foods include:

  • soup
  • smoothies
  • yogurt
  • mashed potatoes
  • oatmeal
  • beans
  • steamed vegetables
  • stewed fruits
  • cheese
  • fish
  • scrambled eggs

Until trismus resolves, it may be beneficial to avoid foods that are hard, crunchy, or chewy, such as candy bars, uncooked apples, and tough meats.

A doctor will carry out a physical examination and take a person’s medical history to diagnose trismus.

They may ask about recent injuries or dental work and look for signs of cancer or abnormalities in the bones or tissues of the jaw.

A doctor may use one or more of the following tests to help them diagnose or rule out trismus:

  • a measurement of the mouth opening
  • a CT scan
  • an MRI scan

Trismus may cause a variety of complications that can affect a person’s quality of life, including:

Oral hygiene problems

If a person cannot open their mouth fully, this makes maintaining oral hygiene more difficult.

Poor oral hygiene can lead to:

  • bad breath (halitosis)
  • dental caries (cavities)
  • infection

Trismus may also make it challenging for those wearing dentures to insert the dentures or remove them for cleaning.

Difficulty eating

If people cannot bite, chew, or swallow properly, there is a chance of malnutrition and dehydration.

Temporarily moving to a predominantly liquid and soft foods diet may help reduce these risks.

Many of the infectious and traumatic causes of trismus may also have associated complications. For example, an odontogenic infection that causes trismus may lead to further infection with facial cellulitis or mandibular osteomyelitis.

Infection

If an infection is the cause of trismus, there may be associated complications, such as cellulitis.

Cellulitis is skin inflammation that is often due to infection. The symptoms include:

  • edema, or swelling
  • reddening of the skin
  • warmth emanating from the infection site
  • pain

Trismus is a painful condition involving a reduction in the size of the mouth opening between the jaws.

Most cases are temporary, and medications, physical therapy, and other treatments can often effectively alleviate trismus and reduce or prevent complications. Early treatment typically provides the best outcomes.

Individuals who have concerns about trismus or their risk of developing it should speak to their doctor or dentist.