​​​​Trismus is a disorder in which it becomes difficult, painful, or impossible to fully open your mouth due to a decrease in the range of motion of the muscles or joints of the jaw. It is one of many possible long-term side effects of treatment for head and neck cancer. Trismus is diagnosed by measuring how wide the mouth opens or by the degree of pain with attempted mouth opening.

What Causes Trismus?

Trismus occurs when radiation and/or surgery for head and neck cancer causes scarring or damage to the jaw muscles or jaw joint, or nerve damage. Trismus is not always an immediate side effect; it may develop immediately upon surgical removal of the jaw or jaw muscles, or it can develop slowly, often unnoticed in its earliest stages, over a period of approximately 12-18 months. Once it begins, it is often irreversible.

It is important to prevent or receive treatment for trismus as soon as possible because it doesn’t take long for muscles and joints to begin deteriorating.  Once they atrophy, the muscles turn into scar tissue, causing loss of functional muscles and jaw joints. Research shows that muscles that are unable to move through their full range of motion will begin to atrophy after as little as 3 days. Joints that are unable to move through their full range of motion quickly begin to degenerate as well. Degeneration can quickly become permanent.

Risk Factors

Trismus will affect between 10% and 40% percent of head and neck cancer patients, with severity varying from person to person.

Risk factors for developing trismus include:

  • Radiation treatment for oral, oropharyngeal, nasopharyngeal, base of tongue, salivary gland, skin of the face and jaw cancers. The structures responsible for trismus (upper and lower jaw and muscles of the jaw) are directly in the radiation field when treating these specific cancers.
  • Radiation dosages higher than 60 Gr.
  • Previous radiation treatment, including patients who are being treated for a recurrence of their cancer.

How Might Trismus Affect Me?

Trismus has the potential to seriously impact one’s health and quality of life.

  • Trismus makes it difficult and painful to chew and swallow, often resulting in inadequate nutrition, significant weight loss, and increasing the risk of aspiration (choking).
  • Speaking becomes difficult due to the inability to fully open the mouth and the associated reduction in vocal quality. You may speak quietly or seem to be mumbling. Your tongue may not be able to make normal speech sounds if your mouth cannot open fully.
  • It may be difficult or impossible to wear dentures.
  • Physical exams of the mouth, including medical and dental exams, may be impossible.
  • It may be difficult or impossible to maintain proper oral hygiene, which is tremendously important to head and neck cancer patients and survivors.
  • Poor oral hygiene can result in dental caries and radiation related osteoradionecrosis of the jaws.


Symptoms of trismus include:

  • Jaw stiffness
  • Reduced ability to open your mouth wide
  • Pain when opening or closing the mouth

Trismus develops very slowly and often goes unnoticed by patients in its earliest stages. So, vigilance is needed to catch it early, when it can still be managed effectively. You may wish to regularly do the “3 finger test” to make sure you can open your mouth fully. Insert 3 fingers vertically into your mouth. If your fingers fit between your top and bottom front teeth, your mouth opening is considered functional.  If you can only fit 2 or fewer fingers, you may be suffering from trismus.

Treatment & Management

If trismus is treated early, patients can minimize their symptoms and prevent it from getting worse. Treatment is generally restricted to stretching or passive motion exercises, with the latter shown to be more effective than static stretching. Recent research at the University of Pittsburgh has also shown that passive motion offers a significant reduction in inflammation and pain as well.

  • Stretching: Many practitioners use tongue depressors to help patients stretch their jaw muscles. The depressors are stacked between the teeth and held in place for a period of time, in an attempt to widen the mouth opening.
  • Passive Motion Devices: Passive motion devices are used to open and close the mouth, working the associated joints and muscles, without the patient exerting any effort. There are a variety of passive motion devices available to patients suffering from trismus, including custom-made options.

Preventing Trismus

Because trismus is irreversible and often goes unnoticed until it is advanced, patients may wish to focus on preventing it early, even during treatment for their cancer. Some exercises that may help prevent trismus include:

  • Open your mouth against gentle pressure by pressing one hand underneath the lower jaw. Place a finger from your other hand on your bottom teeth. Place a finger from the second hand on the top front teeth, and gently pull your mouth open as wide as possible.
  • Open your mouth wide, as if you’re yawning. Keep it open for 2 minutes. Rest for 1 minute and then repeat.
  • Use stacked tongue depressors to help you open your mouth as wide as possible.
  • Use a passive motion device to exercise your jaw and jaw muscles.
  • You may also wish to regularly do the “3 finger test” (see above) to make sure you haven’t lost any range of motion.

Ask your doctor before you begin these, or any other, exercises. If you’ve had surgery, you may have to wait to do any stretching or passive motion exercises until your surgery site has healed.

  • “Trismus - Canadian Cancer Society.”,
  • “Trismus.” The Oral Cancer Foundation, 15 Oct. 2018,