The short answer
Head and neck radiation can leave the jaw stiff. NIDCR says the dental team can show you jaw exercises to prevent and treat stiffness, and NCI says treatment should start as soon as possible.
Jaw stiffness is a known late effect of head and neck radiation. Some mouth problems fade after treatment and others last a long time.
NIDCR says the dental team can show you how to exercise the jaw muscles three times a day, opening and closing as far as possible without pain, 20 times.
NCI says jaw stiffness can follow oral surgery or radiation scarring, and that treatment should begin as soon as possible.
Ask your team how your mouth opening will be measured, so you have your own number to compare against.
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This page is for people who have had, or will have, radiation or surgery for head and neck cancer. It explains jaw stiffness. It also shares what the National Institutes of Health say about preventing it.
What trismus is
Trismus is jaw stiffness that limits how wide the mouth can open. The National Cancer Institute (NCI) puts it in everyday terms. In its list of head and neck treatment effects, it says: "The jaw may feel stiff, and patients may not be able to open their mouth as wide as before treatment."
It can make eating, dental care and speech harder. Dental care is also harder when a dentist cannot get instruments in.
Why radiation and surgery cause it
NCI lists three causes of jaw stiffness. They are oral surgery, late effects of radiation therapy, and stress caused by the cancer and its treatment. Late effects of radiation include fibrosis, which is scar-like tissue. NCI says the risk from radiation rises with higher doses. It also rises with repeated radiation treatments.
Why it should not be left alone
NCI lists what happens when jaw stiffness goes untreated:
- malnutrition and weight loss, from not being able to eat normally
- slower healing and recovery, from poor nutrition
- dental problems, from not being able to clean the teeth and gums well
- weakened jaw muscles, from not using them
- emotional problems, from avoiding social contact because of trouble speaking and eating
It can last, so keep checking
The National Institute of Dental and Craniofacial Research (NIDCR) lists jaw stiffness among the possible mouth side effects of head and neck radiation. It says some problems go away after treatment. Others last a long time. Some may never go away. So do not stop watching your jaw when treatment ends.
Catching a change early
Jaw opening changes slowly. Slow changes are easy to miss. Ask your team how they want your mouth opening measured and how often. A number from before treatment gives you something to compare against.
Tell your team if your mouth opens less than it did. Tell them if eating has changed (softer foods, smaller bites). Tell them if a dentist has trouble getting access. NCI says treatment for jaw stiffness should begin as soon as possible. This helps keep it from getting worse or becoming permanent.
Jaw exercises
NIDCR says your dental team can show you how to prevent and treat jaw stiffness. You exercise the jaw muscles three times a day. Each time, you open and close the mouth as far as possible (without causing pain) 20 times.
Note the wording: without causing pain. Programs differ between centers. Use the one your team gave you rather than mixing several. If stretching hurts, ask your team. Ask them too if you are not sure you are doing it right.
Devices and specialist help
NCI lists several ways to treat jaw stiffness. These are medical devices for the mouth, pain treatments, medicine to relax muscles, jaw exercises and medicine to treat depression. Ask your oncologist, dentist or nurse whether a device is right for you. Ask too about a referral to a therapist who treats jaw stiffness.
When to call
If you notice any tightening in your jaw, call your care team right away. NIDCR also advises talking regularly with your cancer doctor and dentist about any mouth problems during and after head and neck radiation. Ask them about medicines to help control pain.
NIDCR advises seeing a dentist before treatment, ideally 1 month before your first radiation treatment. If you have already started radiation, see one as soon as possible. Dental care remains part of your long-term follow-up care.
Sources
- National Institute of Dental and Craniofacial Research (NIDCR): Head and Neck Radiation Treatment and Your Mouth
- National Cancer Institute (NCI): Head and Neck Cancers
- National Cancer Institute (NCI): Oral Complications of Chemotherapy and Head/Neck Radiation (PDQ) Patient Version
Common questions
What is trismus?
Trismus is jaw stiffness that limits how wide the mouth can open. NCI describes it in everyday terms: the jaw may feel stiff, and patients may not be able to open their mouth as wide as before treatment.
Why does treatment cause it?
NCI lists three causes: oral surgery, late effects of radiation therapy such as fibrosis (fibrous, scar-like tissue), and stress caused by the cancer and its treatment. NCI also says the risk from radiation rises with higher doses and with repeated radiation treatments.
Can it start after treatment is finished?
NIDCR says some mouth problems from head and neck radiation go away after treatment, while others last a long time and some may never go away. NCI describes fibrosis as a late effect of radiation. So keep mentioning your jaw at follow-up visits.
How can I tell if my jaw opening is changing?
Ask your team how they want it measured and how often. A number written down before treatment gives you something to compare against later. If your mouth opens less than it did, tell your team.
Why start jaw exercises before anything feels wrong?
NIDCR says the dental team can show you how to prevent and treat jaw stiffness by exercising the jaw muscles three times a day. You open and close the mouth as far as possible, without causing pain, 20 times. NCI says treatment for jaw stiffness should begin as soon as possible to keep it from getting worse or becoming permanent.
Why does it matter if I can live with a smaller mouth opening?
NCI warns that untreated trismus can cause malnutrition and weight loss, make dental care difficult, weaken the jaw muscles, and lead to emotional problems that affect social interaction. The knock-on effects are the real concern.
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Written by: Cancer ExplainedSources last checked: 2026-10-02 what this meansLast updated: 2026-10-16Next planned review: 2027-01-28
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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