Trismus, or lockjaw, refers to reduced opening of the jaws caused by spasm of the muscles of mastication, or may generally refer to all causes of limited mouth opening. It is a common problem with a variety of causes, and may interfere with eating, speech, oral hygiene, and could alter facial appearance. There is an increased risk of aspiration. Temporary trismus is much more common than permanent trismus and may be distressing and painful, and limit or prevent medical examination or treatments requiring access to the oral cavity.Trismus means being unable to open the mouth completely. It can be caused by muscle, nerve or joint damage.

Trismus is not a disease. It is a symptom of another problem.

Trismus can be caused by:

  • Trauma (injury) to the face and/or jaw
  • Problems with the jaw joint (also known as the temporomandibular joint, or TMJ) — This is one of the most common causes of trismus.
  • Surgery
  • A tumor in the jaw area (of soft tissue or bone)
  • Local muscle soreness from clenching or grinding the teeth (bruxism)
  • A local anesthetic shot, if the needle nicks the muscle tissue or a blood vessel and causes some internal bleeding
  • Radiation therapy to the head and neck — Of people who receive such radiation, 10% to 40% will develop trismus.
  • Infection
  • Diseases that affect the whole body, particularly central nervous system disorders or autoimmune diseases such as lupus
  • Tetanus (lockjaw)
  • Trismus often develops slowly. For example, it can occur in someone who is receiving radiation. For this reason, it may go unnoticed for some time. Trismus also can develop suddenly.
  • An example would be someone who is in a car accident and has trauma to the jaw.
  • In certain cases, if trismus is left untreated, problems with swallowing, speech and oral hygiene can develop.


Difficulty opening the mouth is the main sign of trismus. Problems with speech and/or swallowing also can occur in severe cases. The severity of trismus depends on its cause. Pain also can be a symptom.


Your dentist or physician will discuss your medical history leading up to the trismus and do a physical examination. Head and neck imaging may be needed to detect the cause. These may include:

  • Panoramic X-rays
  • Magnetic resonance imaging (MRI) scans
  • Computed tomography (CT) scans

Expected Duration

How long trismus lasts depends on its cause. For example, trismus from muscle soreness (caused by clenching orgrinding the teeth) may disappear in as little as a week. Trismus caused by radiation therapy or trauma will take longer to go away.


The way to prevent trismus is to prevent the cause. This is not always possible. If you clench or grind your teeth, a bite splint may prevent trismus. This is a plastic device that changes the position of your lower jaw so you don’t grind or clench your teeth. It’s worn while you sleep.

People who get radiation therapy to the head and neck can undergo physical therapy for the jaw. This will decrease the risk of trismus.

To help prevent trismus, make sure to get treatment for any signs of infection in the jaw. Signs of infection include:

  • Pain
  • Swelling
  • Warmth in the area
  • Redness


Treatment depends on the cause of the trismus. Tests to diagnose the cause should begin as soon as possible. Otherwise, the condition can get worse. This makes treatment more difficult.

Many devices can be used to open the mouth gradually. They vary in cost, function and how well they work. They are not prescribed in every case.

Exercises usually are prescribed. They should be done several times a day. They may be required for many months to ensure that the trismus does not get worse or return. In more severe cases, physical therapy and muscle relaxants may be prescribed.

When To Call a Professional

A health care professional should evaluate any episode of trismus, particularly if it is sudden. If you have trouble opening your mouth, contact your doctor or dentist. Specialists in orofacial (mouth and face) pain are specifically trained to diagnose and treat this problem.


The outlook for trismus varies greatly, depending on the cause. Infections and jaw-joint inflammations that are treated early have an excellent prognosis. Delayed treatment can lead to a poor prognosis.