Trismus

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What is trismus?

Trismus (sometimes called lockjaw) is a condition that makes it hard to open the mouth fully. It can happen anytime during treatment, soon after treatment, or years later. Trismus can be mild or severe.

Causes of trismus

Trismus can be caused by:

Radiation to the head and neck
Surgery to the face, jaw, or neck
A tumor that affects the nerves, bones, or muscles that open the mouth
Scar tissue
Some medicines

Symptoms of trismus

Tell your medical team right away if your child has:

Problems opening their mouth
Tightness or pain in their mouth or jaw

If your child has radiation to the head and neck, they might see a speech therapist when radiation starts. The therapist can teach exercises to help prevent trismus.

Photo of someone testing for trismus — If your child cannot put 3 fingers in their mouth, they might have trismus.

A test for trismus

Most people can open their mouth about 3 fingers wide. To test for trismus, have your child hold their 3 middle fingers sideways. Then, have them put all 3 in their mouth with fingernails pointing toward the throat. If all three fingers fit between the top and bottom front teeth, your child has a normal mouth opening. If your child cannot put 3 fingers in their mouth, they might have trismus.

Problems caused by trismus

Trismus can affect your child’s comfort and quality of life. It can also cause:

Weakness and fatigue when chewing or talking
Jaw pain
Cavities, mouth infections, and bad breath due to difficulty cleaning the mouth and teeth
Problems opening the mouth for checkups and treatment
Chewing and swallowing problems, causing weight loss or choking risks
Speech problems if they cannot open their mouth wide enough to make normal sounds
Problems putting in a breathing tube if it is needed for medical treatment

Treatment for trismus

The earlier your child begins treatment for trismus, the more likely it is to help. Treatments for trismus include:

Gentle exercises to stretch the jaw or neck
Medical devices such as TheraBite®
Jaw muscle massage to help the muscles relax
Ice or heat

Your child’s health care provider can tell you if your child needs these treatments and how to do them.

To learn more about trismus, talk with your care team.

Key points about trismus

Trismus is a condition where jaw muscles are tight. This makes it hard to open the mouth fully.
Trismus can be caused by surgery, radiation, a tumor, scar tissue, or some medicines.
If you suspect that your child has trismus, tell your health care provider.
The earlier treatment begins for trismus, the more likely it is to help.

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Reviewed: October 2022