Definition and General Information
- Trismus is a painful restriction in opening the mouth due to muscle spasm.
- It can refer to limited mouth opening of any cause.
- 'Lockjaw' is sometimes used as a synonym for trismus and tetanus.
- Normal mouth opening ranges from 35 to 45mm.
- Males usually have slightly greater mouth opening than females.

Intra-articular Causes of Trismus
- Internal derangement of TMJ / meniscus displacement.
- Fractured mandibular condyle or intracapsular fracture.
- TMJ dislocation.
- Traumatic synovitis.
- Septic arthritis.

Extra-articular Causes of Trismus
- Trauma not involving the mandibular condyle.
- Post-surgical edema.
- Recent prolonged dental treatment.
- Following administration of inferior alveolar nerve block.
- Acute infections of the oral tissues.

Joint Problems Causing Trismus
- Ankylosis can result from trauma, infections, and prolonged immobilization.
- Treatment for bony ankylosis includes surgical procedures like gap arthroplasty.
- Fibrous ankylosis usually results from trauma and infection.
- Treatment for fibrous ankylosis involves trismus appliances and physical therapy.
- Arthritis synovitis and meniscus pathology are also joint problems that can cause trismus.

Miscellaneous Causes of Trismus
- Infections, such as odontogenic, peritonsillar abscess, and tetanus.
- Dental treatment, including dental trismus caused by injury to the masticatory muscles.
- Trauma, such as fractures and accidental incorporation of foreign bodies.
- TMJ disorders, including myofascial pain dysfunction syndrome.
- Tumors and fibrosis, which can cause limited mouth opening.
- Drug therapy, where certain medications can cause trismus as a side effect.
- Complications of radiotherapy and chemotherapy, which can lead to decreased mouth opening.
- Congenital and developmental causes, such as hypertrophy of the coronoid process.
- Hysteric patients, where emotional conflicts can manifest as physical symptoms like trismus.
- Scleroderma, a condition marked by edema and induration of the facial skin, can cause trismus.

Trismus (Wikipedia)

Trismus is a condition of restricted opening of the mouth. The term was initially used in the setting of tetanus. Trismus may be caused by spasm of the muscles of mastication or a variety of other causes. Temporary trismus occurs much more frequently than permanent trismus. It is known to interfere with eating, speaking, and maintaining proper oral hygiene. This interference, specifically with an inability to swallow properly, results in an increased risk of aspiration. In some instances, trismus presents with altered facial appearance. The condition may be distressing and painful. Examination and treatments requiring access to the oral cavity can be limited, or in some cases impossible, due to the nature of the condition itself.

Trismus
Other names	Lockjaw
Trismus caused due to muscle rigidity. Diagram of jaw muscles are shown here.