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Many muscles and nerves work together to open and close your mouth. When these muscles are damaged, your child might get a condition called “trismus.”

What is trismus and what causes it?

Trismus is a condition that makes it hard to open the mouth. It can happen from damage to the nerves or a joint such as the “temporomandibular joint,” or TMJ. It can also happen from damage to jaw muscles, fast growing scar tissue, or a combination of these things. It can happen during your child’s treatment, right after treatment, or years later.


Common causes of trismus include:

  • Surgery to the head, neck, or jaw, 
  • Radiation for head and neck cancer, 
  • Surgery on the face, 
  • A tumor that affects the bones, muscles, and nerves that open the mouth, and 
  • Some medicines. The picture at the right shows the upper and lower jaw. It also shows the “temporomandibular joint,” or TMJ.

Will my child get trismus?

Maybe not. Some people who have head and neck cancer treatment do not get trismus. Trismus can be mild or severe. So your child might be able to open his mouth as much as he wants. Or he might have just a small opening.

Should I watch for signs of trismus in my child?

Yes. Doctors know that when muscles do not move normally for 3 days or more, they start wasting away. In the same way, joints that do not move start to break down. Trismus can happen any time during your child’s treatment or even years after treatment if he had radiation. You should watch for signs that your child is having problems opening his mouth. Once trismus develops, it is very hard to treat. So it is important to prevent trismus and to treat it as early as possible. Your child might see a speech therapist when radiation starts. The therapist can teach exercises to help prevent trismus.


Trismus test

A simple test for trismus

Most people can open their mouths about 3 fingers wide. To test for trismus, have your child hold his 3 middle fingers sideways. Then, have him put all 3 in his mouth with his 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 his mouth, he might have trismus.

What problems can trismus cause?

Trismus can affect your child’s quality of life, make him less comfortable, or both. When your child cannot open his mouth, it is hard for the doctor to examine this area. The list below tells you about other problems from trismus.

  • Weakness – Your child might get tired easily when chewing or talking. 
  • Bad breath, cavities, and mouth infections – Trismus makes it hard to clean the mouth and teeth completely. 
  • Problems with dental checkups and treatment. 
  • Chewing problems – Your child might lose weight or be at risk of choking if he has trouble chewing food. 
  • Speech problems – The mouth cannot open enough to make normal sounds. 
  • Problems putting in a breathing tube – If your child needs a breathing tube for medical treatment. 
  • Jaw pain.

What is the treatment for trismus?

Early treatment is more likely to help. It is also easier for your child. The list below gives some treatments for trismus. Your child’s doctor or therapist can tell you if your child needs these treatments and how to do them.

  • Exercises to stretch the jaw gently. Your child can use certain medical devices to help, such as the TheraBite®. If your child needs a TheraBite®, the doctor can prescribe one. 
  • Jaw muscle massage – This helps the muscles relax. 
  • Ice or heat.


If you have questions about trismus, talk with your medical team or call Rehabilitation Services at 901-595-3621.


This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

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