Common causes

• Pericoronitis
  Pericoronitis
  Pericoronitis is a common problem in young adults with partial tooth impactions. It usually occurs within 17 to 24 years of age as it is when the third molars start erupting. It occurs when the tissue around the wisdom tooth has become inflamed because bacteria have invaded the area. Poor oral...
  
   (inflammation of soft tissue around impacted third molar) is the most common cause of trismus.
• Inflammation of muscles of mastication. It is a frequent sequel to surgical removal of mandibular third molars (lower wisdom teeth). The condition is usually resolved on its own in 10–14 days, during which time eating and oral hygiene
  Oral hygiene
  Teeth cleaning is part of oral hygiene and involves the removal of dental plaque from teeth with the intention of preventing cavities , gingivitis, and periodontal disease. People routinely clean their own teeth by brushing and interdental cleaning, and dental hygienists can remove hardened...
  
   are compromised. The application of heat (e.g. heat bag extraorally, and warm salt water intraorally) may help, reducing the severity and duration of the condition.
• Peritonsillar abscess
  Peritonsillar abscess
  Peritonsillar abscess , also called a quinsy or abbreviated as PTA is a recognised complication of tonsillitis and consists of a collection of pus beside the tonsil .-Symptoms and signs:...
  
  , a complication of tonsillitis
  Tonsillitis
  Tonsillitis is an inflammation of the tonsils most commonly caused by viral or bacterial infection. Symptoms of tonsillitis include sore throat and fever. While no treatment has been found to shorten the duration of viral tonsillitis, bacterial causes are treatable with antibiotics...
  
   which usually presents with sore throat, dysphagia
  Dysphagia
  Dysphagia is the medical term for the symptom of difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, the term is sometimes used as a condition in its own right. Sufferers are sometimes unaware of their dysphagia....
  
  , fever
  Fever
  Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
  
  , and change in voice.
• Temporomandibular joint disorder
  Temporomandibular joint disorder
  Temporomandibular joint disorder , or TMJ syndrome, is an umbrella term covering acute or chronic inflammation of the temporomandibular joint, which connects the mandible to the skull. The disorder and resultant dysfunction can result in significant pain and impairment...
  
   (TMD)
• Trismus is often mistaken as a common temporary side effect of many stimulants of the sympathetic nervous system. Users of amphetamines as well as many other pharmacological agents commonly report bruxism
  Bruxism
  Bruxism is characterized by the grinding of the teeth and typically includes the clenching of the jaw. It is an oral parafunctional activity that occurs in most humans at some time in their lives. In most people, bruxism is mild enough not to be a health problem...
  
   as a side-effect; however, it is sometimes mis-referred to as trismus. User's jaws do not lock, but rather the muscles become tight and the jaw clenched. It is still perfectly possible to open the mouth.
• Submucousfibrosis.

Other causes

• Acute osteomyelitis
  Osteomyelitis
  Osteomyelitis simply means an infection of the bone or bone marrow...
  
  
• Ankylosis
  Ankylosis
  Ankylosis or anchylosis is a stiffness of a joint due to abnormal adhesion and rigidity of the bones of the joint, which may be the result of injury or disease. The rigidity may be complete or partial and may be due to inflammation of the tendinous or muscular structures outside the joint or of...
  
   of the TMJ (fibrous or bony)
• Condylar
  Condyloid process
  The condyloid process is part of the mandible and is thicker than the coronoid, and consists of two portions: the condyle, and the constricted portion which supports it, the neck.-Condyle :...
  
   fracture or other trauma.
• Gaucher disease which is caused by deficiency of the enzyme glucocerebrosidase
  Glucocerebrosidase
  β-Glucocerebrosidase is an enzyme with glucosylceramidase activity that is needed to cleave, by hydrolysis, the beta-glucosidic linkage of the chemical glucocerebroside, an intermediate in glycolipid metabolism...
  
  .
• Giant cell arteritis
• Infection
• Local anesthesia
  Local anesthesia
  Local anesthesia is any technique to induce the absence of sensation in part of the body, generally for the aim of inducing local analgesia, that is, local insensitivity to pain, although other local senses may be affected as well. It allows patients to undergo surgical and dental procedures with...
  
   (dental injections into the infratemporal fossa)
• Needle prick to the medial pterygoid muscle
  Medial pterygoid muscle
  The medial pterygoid , is a thick, quadrilateral muscle of mastication.The mandibular branch of the fifth cranial nerve, the trigeminal nerve, innervates the medial pterygoid muscle.-Origin and insertion:...
  
  
• Oral submucous fibrosis.
• Radiation therapy
  Radiation therapy
  Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
  
   to the head and neck.
• Tetanus
  Tetanus
  Tetanus is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, rod-shaped, obligate anaerobic bacterium Clostridium tetani...
  
  
• Malignant hyperthermia
  Malignant hyperthermia
  Malignant hyperthermia or malignant hyperpyrexia is a rare life-threatening condition that is usually triggered by exposure to certain drugs used for general anesthesia; specifically, the volatile anesthetic agents and the neuromuscular blocking agent, succinylcholine...
  
  
• Malaria severa
• Secondary to neuroleptic drug use
• Malignant otitis externa
• Retropharyngeal or parapharyngeal abscess
• Seizure
  Seizure
  An epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
  
  

Treatment