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Trismus is difficulty opening the mouth. Trismus may also be called restricted mouth opening. Trismus can be a side effect of head and neck cancers.


Head and neck cancers can cause trismus, or it can be a side effect of treatment for these cancers. Trismus can also be caused by conditions such as tetanus, arthritis and infections of the mouth and throat. Scarring of the lining inside the mouth caused by chewing betel quid (areca nut) or damage to the jaw muscles or jaw joint (temporomandibular joint or TMJ) can also cause trismus.

When it is related to cancer, trismus can be caused by:

  • tumours that grow into the jaw muscles or jaw joint
  • surgery to remove the tumour
  • radiation therapy to treat the tumour

Radiation therapy is the most common cause of cancer-related trismus. Radiation therapy can cause scar tissue to form in the jaw muscles, making them stiff. This makes it hard to move your jaw and open your mouth. Your risk of developing trismus is related to how much radiation you received. Higher radiation doses mean a higher risk. Having radiation therapy again for another cancer in the same area also increases your risk.


Symptoms of trismus can vary depending on their cause and other factors. Symptoms of trismus include:

  • stiff jaw
  • not being able to open the mouth wide
  • pain when trying to open the mouth

Trismus develops slowly after treatment has finished and usually gets worse over time. It can become a long-term problem.

Trismus can affect your quality of life. It can cause problems with:

  • talking
  • chewing
  • swallowing
  • taking care of your teeth

If you can't open your mouth properly, other people may find it hard to understand you when you talk. Trismus can also cause problems with eating. You may only be able to put a small amount of food in your mouth. This can lead to problems with nutrition and cause you to lose weight. Not being able to fully open your mouth can make it hard to brush and floss your teeth and have a dental checkup. This can lead to dental problems.


Your healthcare team may measure how wide you can open your mouth. Changes in this measurement let you and the healthcare team know if your trismus is getting better or worse.

Preventing and managing trismus

It is best to prevent trismus from developing. Your healthcare team can suggest ways to try to prevent trismus and ways to manage it if you develop it. Tell your healthcare team if you have jaw stiffness or pain. You may be referred to a physiotherapist, speech therapist or dentist to help manage your trismus. Trismus can become permanent if it's not treated.


Your healthcare team may give you exercises to help prevent and improve jaw stiffness. How well the exercises work depends on:

  • how often you do them
  • how soon after treatment you start them (the sooner, the better)

Here are some sample exercises:

  • Open your mouth as wide as possible. Do this 20 times. Repeat 3 times a day.

  • Place the heel of your palm under your jaw and push up while stretching the mouth open. Do this 20 times. Repeat 3 times a day.
  • Place your middle and index fingers on your lower teeth and your thumb on your upper teeth. Use your fingers to pry your mouth open. Hold it open as wide as possible for 2 seconds and then relax. Do this 10 times with each hand. Repeat 4 times a day.

If your healthcare team gives you exercises to do at home, it's important to follow their instructions. The exercises above can help prevent and improve jaw stiffness, but your healthcare team may suggest ones that are better for you.

Your healthcare team may also prescribe medicines to help with pain and muscle spasms. This can help make it easier for you to do your exercises.

Jaw-stretching devices

You may be able to help stretch your jaw muscles by using a device that you put in your mouth. The device stretches the jaw muscles for you.

Some research shows that people with trismus who use these devices regularly can improve their ability to open their mouth and their quality of life.

Talk to your healthcare team about whether these devices are right for you, where to get them and how to use them.


If you have severe trismus that does not get better with exercises, you may be able to have surgery to try to improve it.

Expert review and references

  • Iona Leong, BDS, MSc, FRCD

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