Trismus: Causes,Signs, Symptoms and Management of Lock Jaw

trismusTrismus is a condition where the affected individual is unable to open the mouth completely. Whenever there is a restriction of normal oral opening the term ‘trismus’ is used.

This condition is sometimes referred to as lockjaw because of the reduced opening of the jaws. Medical Dictionaries describe this condition as a tonic contraction of the muscles of mastication.

Although there are many causes for the lockjaw condition, the main reason is the spasm of muscles of mastication. The causes of trismus are extra-articular, meaning, they are located outside the joints (TMJ in this case) and that’s the reason why it is sometimes called as false ankylosis.

Trismus Causes

There are many conditions which may result in trismus. Below are some of the important ones.


The infections in the orofacial regions around the area of the temporomandibular joint commonly result in limited mouth opening.  The infections arising from structures in and around the teeth (odontogenic infections) can also lead to trismus. Most common odontogenic infections belonging to this category are pericoronitis, Ludwig’s angina, etc.

Other infections that may result in limited jaw movements are a Sub masseteric and infratemporal abscess, chronic infections of the jaw bones such as Tuberculous osteomyelitis of ramus and/or body of the mandible, etc.


In case of fracture of the zygomatic arch, there may be an impingement on the coronoid process. This may result in the restricted mouth opening. Coronoid process is a thin, triangular eminence on the border of the mandible.  Fracture of the lower jaw will also mostly result in limited mouth opening because of associated pain and muscle spasms.

coronoid process

Myositis Ossificans

This is a condition where the bone tissue may form inside a muscle or a soft tissue following an injury or trauma. This is more common in young adults and athletes.

When there is an injury to the Temporomandibular joint or the nearby area a hematoma may be formed inside the masticatory muscle group. This hematoma may later progress into ossification and cause stiffness of muscles leading to trismus.


Myositis or muscular atrophy belongs to this category.


Hypocalcemia is a condition characterized by significantly lower calcium levels in the blood serum and Tetany is one of the common side effects of Hypocalcemia. Tetany involves muscular spasms affecting various parts of the body. Carpopedal spasm along with trismus is one of its main features.


This is a completely different condition from Tetany mentioned above. Tetanus is a serious condition caused by bacterial toxins. The bacteria responsible for this life-threatening disease is Clostridium tetani.

Tetanus is characterized by painful muscle contractions which mainly affect the jaw and neck areas. Due to these muscular contractions, the individual isn’t able to open the mouth because of which Tetanus is also termed as ‘LockJaw’.  The affected individual may even find it difficult to breathe normally.

Mechanical Causes

Anatomical defects associated with the coronoid process of the mandible give rise to trismus.

  • Elongation of coronoid process
  • Exostosis
  • Osteoma
  • Osteochondroma of coronoid process



Conditions which result in fibrosis of muscles outside the jaw joints may also lead to trismus. The important ones belonging to this category are as follows.

  • Oral submucous fibrosis
  • Chronic cervicofacial sepsis
  • Sphenomandibular ligament ossification
  • Post radiation therapy

Neurological Problems

Following neurological conditions may limit the mouth opening.

  • Epilepsy
  • Brain tumor
  • Bulbar paralysis
  • Embolic hemorrhage in the medulla oblongata

Trismus Caused Due to Drug Poisoning

Use of certain drugs in excess may cause drug poisoning may result in muscular spasms leading to limited mouth opening. Strychnine poisoning is one such example.

Psychosomatic Reasons

Inability to open mouth in these conditions is termed as trismus hystericus. It is a condition caused due to extreme fear and anxiety associated with hysterical fits.

Signs and Symptoms of Trismus

Following are the most common signs and symptoms of Trismus.

  • Inability to open the mouth is the main sign and symptom of this condition.
  • Pain on trying to open the mouth.
  • Painful jaws
  • Difficulty to eat, chew or swallow food
  • Difficulty in speaking
  • The TMJ area may be tender to touch from the outside
  • Bad breath may be associated with trismus due to lack of oral hygiene measures.

lock jaw


The signs and symptoms associated with trismus disappear once the cause has been cured.  To manage the symptoms of lockjaw for faster relief the doctor may prescribe muscle relaxants and analgesics. Steroidal injections may also be given intramuscularly for faster relief, depending on the severity.

Jaw stretching devices may be used as required. Physical therapy measures involving jaw stretching exercises and massaging may be implemented.

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