In these cases it is usually the medial pterygoid or the buccinator muscles. Oral surgery procedures, as in the extraction of lower molar teeth, may cause trismus as a result either of inflammation to the muscles of mastication or direct trauma to the TMJ. Barbing of needles at the time of injection followed by tissue damage on withdrawal of the barbed needle causes post-injection persistent paresthesia, trismus and paresis. Treatment: in acute phase:
Heat therapy
Analgesics
A soft diet
Muscle relaxants (if necessary)
Note: When acute phase is over the patient should be advised to initiate physiotherapy for opening and closing mouth. Trauma
Fractures, particularly those of the mandible and fractures of zygomatic arch and zygomatic arch complex, accidental incorporation of foreign bodies due to external traumatic injury. Treatment: fracture reduction, removal of foreign bodies with antibiotic coverage

TMJ disorders
Extra-capsular disorders – Myofascial pain dysfunction syndrome
Intra-capsular problems – Disc displacement, arthritis, fibrosis,  etc. Acute closed locked conditions – displaced meniscus

Tumors and oral care
Rarely, trismus is a symptom of nasopharyngeal or infratemporal tumors/ fibrosis of temporalis tendon, when patient has limited mouth opening, always premalignant conditions like oral submucous fibrosis (OSMF) should also be considered in differential diagnosis. Drug therapy
Succinyl choline, phenothiazines and tricyclic antidepressants causes trismus as a secondary effect. Trismus can be seen as an extra-pyramidal side-effect of metoclopromide, phenothiazines and other medications. Radiotherapy and chemotherapy
Complications of radiotherapy:
Osteoradionecrosis may result in pain, trismus, suppuration and occasionally a foul smelling wound. When muscles of mastication are within the field of radiation, it leads to fibrosis and result in decreased mouth opening.
Differential diagnosis
Traditionally causes of trismus are divided into intra-articular (factors within the temporomandibular joint [TMJ]) and extra-articular (factors outside the joint, see table). Joint problems
Ankylosis
True bony ankylosis: can result from trauma to chin, infections and from prolonged immobilization following condylar fracture
Treatment – several surgical procedures are used to treat bony ankylosis, e.g. : Gap arthroplasty using interpositional materials between the cut segments. Fibrous ankylosis: usually results due to trauma and infection
Treatment – trismus appliances in conjunction with physical therapy. Arthritis synovitis
Meniscus pathology
Extra-articular causes
Infection
Odontogenic- Pulpal
Periodontal
Pericoronal
Non-odontogenic- Peritonsillar abscess
Tetanus
Meningitis
Brain abscess
Parotid abscess
The hallmark of a masticatory space infection is trismus or infection in anterior compartment of lateral pharyngeal space results in trismus. If these infections are unchecked, can spread to various facial spaces of the head and neck and lead to serious complications such as cervical cellulitis or mediastinitis. Treatment: Elimination of etiologic agent along with antibiotic coverage
Trismus or lock jaw due to masseter muscle spasm, can be a primary presenting symptom in tetanus, Caused by Clostridium tetani, where tetanospasmin (toxin) is responsible for muscle spasms. Prevention: primary immunization (DPT)

Dental treatment
Dental trismus is characterized by a difficulty in opening the jaw. It is a temporary condition with a duration usually not longer than two weeks. Dental trismus results from some sort of insult to the muscles of mastication, such as opening the jaw for a period of time or having a needle pass through a muscle. Typical dental anesthesia to the lower jaw often involves the needle passing into or through a muscle.