What is trismus?

Trismus means being unable to open the mouth completely. Normal full jaw opening is 40 – 50 millimetres. The measurement is taken from the edge of the lower front teeth to the edge of the upper front teeth. Trismus is not a disease, it occurs as a result of many different conditions.

What causes trismus?

Trismus can be caused by damage to the muscles and/or nerve responsible for opening and closing the mouth and for chewing.

What is the cause of trismus in people with facial palsy?

Damage to the nerves or muscles responsible for opening and closing the mouth in facial palsy occurs as a result of the following:

  • Surgery to the head, neck, jaw or face.
  • Radiation for treatment of head and neck cancer.
  • Surgical procedures to reanimate the face (such as Labbé reanimation surgery).

What are the symptoms?

  • Difficulty opening your mouth
  • Jaw pain or stiffness.
  • Difficulty eating or chewing.
  • Difficulty brushing your teeth.
  • Difficulty with speaking.

What is the treatment for trismus?



Your GP or consultant should confirm the diagnosis of trismus and he/she may recommend the following treatment. You may also be referred to a speech and language therapist or physiotherapist to help with your treatment.

The main treatment for trismus is jaw exercises to gently help improve mouth opening. There are some specific medical devices that can be particularly helpful. This can be ordered by your GP or the hospital consultant involved in your care. One example of this device is a TheraBite.

A TheraBite provides a balanced, gentle stretch to the jaw muscles without using your own muscles. This is called ‘passive movement’ because you allow the device to move the muscles which you are having difficulty moving. Passive movement or stretching helps relieve stiffness and tightness in the joint and muscles. In doing so it enables you to open your mouth more easily and fully. This improves your ability to eat, speak and brush your teeth, returning jaw function to normal.

In addition, your doctor may prescribe painkillers or anti-inflammatory medication which will make it easier for you to do your exercises.


  • Your jaw will always feel stiffer in the morning because it has been rested overnight.
  • The first jaw stretches of the day will always be more difficult and a little bit tender.
  • You will need to carry out your stretches regularly throughout the day for several weeks or months.
  • When doing any jaw exercises there will be a little discomfort but it should not be intensely painful.
  • If your jaw exercises are causing pain then you are probably stretching too far or too quickly.
  • Just increase the range of your stretches gently by one or two millimetres each week.
  • If you are overenthusiastic you will cause unnecessary pain which will stop you doing your exercises.
  • Stretching before meals often makes eating easier.
  • It is important to use any medical device under medical supervision to ensure you gain the maximum benefit and to reduce harm.

Other exercises

The exercises listed below can be effective in helping you regain full jaw function.

Springy bites

  • Gently places your index finger between your top and bottom front teeth with the nail under your top front teeth.
  • Now gently practice little springy bites to start using the jaw muscles.
  • Do not bite down hard on your finger, just little movements so your top and bottom teeth are just squeezing your finger.
  • Do this for one minute frequently throughout the day.

As this becomes easier you can increase the range of movement as follows:

  • Turn your index finger onto the side so you increase the stretch and follow the same procedure as above.
  • To further increase the stretch use the flat of your thumb then turn your thumb onto its side to widen the stretch further.
  • Finally use two fingers or your thumb and finger between your top and bottom front teeth.

Wooden spatulas

Your speech and language therapist or physiotherapist may provide you with wooden spatulas which measure one millimetre in thickness. You can do passive jaw exercises by inserting the required number of spatulas between your teeth to produce a stretch.

Ask your local speech and language therapist or physiotherapist for help and advice. If you do not have access to these services please ask your GP or hospital consultant to refer you.

Last reviewed: 30-07-2018    ||    Next review due: 30-07-2020