Trismus, commonly called lockjaw.

Refers to a reduced limited jaw range of motion.


It may be caused by spasm of the muscles of mastication or other causes.


It is defined as painful restriction in opening the mouth due to a muscle spasm, however it can also refer to limited mouth opening of any cause.


Temporary trismus occurs much more frequently than permanent trismus.


Trismus interfere with eating, speaking, maintaining proper oral hygiene, swallowing properly, with an increased risk of aspiration. 


It may alter facial appearance. 


It may be distressful  and painful for the patient. 


Access to the oral cavity can be limited, or impossible.


The normal  mouth-opening ranges from 35 to 45 mm.


Males usually have slightly greater mouth opening than females. 


Normally the mouth has lateral movement is 8-12 mm.


The mouth’s protrusive movement is approximately 10 mm.


Mild trismus designated as 20–30 mm interincisal opening, and moderate as 10–20 mm and severe as less than 10 mm.


Trismus causes: 


Intra-articular factors within the temporomandibular joint.


Extra-articular factors outside the joint.


Commonly listed causes of trismus




Internal derangement of TMJ 


Meniscus displacement.


Fractured mandibular condyle or intracapsular fracture.


TMJ dislocation.


Traumatic synovitis.


Septic arthritis.




Inflammatory arthritis of rheumatoid or psoriatic arthritis.




Osteophyte formation.


Extra-articular factors:


Trauma not involving the another part of the mandible, 


Fractures of the middle third of the facial skeleton


Fractures of the zygoma or zygomatic arch.


Post surgical edema.


Recent prolonged dental treatment


Following administration of inferior alveolar nerve block with local anesthetic.


Acute infections of the oral tissues; buccal space or muscles of mastication.


Odontogenic infection


Peritonsillar abscess.


Acute parotitis




Submasseteric abscess






Local malignancy


Myofascial pain / temporomandibular joint dysfunction.


Radiation fibrosis


Fibrosis from burns.


Submucous fibrosis.


Systemic sclerosis.


Myositis ossificans.


Coronoid hyperplasia.


Malignant hyperpyrexia.


Epidermolysis bullosa.


Psychotic disturbances, hysteria.




Treatment – trismus appliances in conjunction with physical therapy.


With masticatory space infection 


elimination of infectious agent agent with antibiotic coverage.


Trismus due to masseter muscle spasm in tetanus, caused by Clostridium tetani, where toxin is responsible for muscle spasms requires antitoxin, antibiotics, tetanus vaccine and anti spasm medications.


Prevention of tetanus related trismus by  primary immunization (DPT).


Dental trismus is a temporary condition, not longer than two weeks associated with difficulty in opening the jaw.


Dental trismus is the result of an insult to the muscles of mastication: opening the jaw for a prolonged period of time or having an anesthetic needle pass through a muscle. 


Dental trismus usually involves the medial pterygoid or the buccinator muscles.


Oral surgery procedures,may trigger  trismus as a result either of inflammation to the muscles of mastication or direct trauma to the TMJ.


Needle injections followed by tissue damage on withdrawal of the needle causes post-injection persistent paresthesia, trismus and paresis.


Rarely, trismus is related to nasopharyngeal or infratemporal tumors/ fibrosis of temporalis tendon, when patient has limited mouth opening.


Drugs such as succinyl choline, phenothiazines and tricyclic antidepressants causes trismus as a secondary effect, and can be seen as an extra-pyramidal side-effect of metoclopromide, phenothiazines and other medications.


Treatment of dental trimus:


Heat therapy




A soft diet


Muscle relaxants 


Physiotherapy for opening and closing mouth.


Trauma related trismus:


Fractures, 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.


Osteoradionecrosis may result in pain, trismus.


When muscles of mastication are within the field of radiation, it can manifest with fibrosis and result in decreased mouth opening.


Scleroderma, with marked by edema and induration of the skin involving facial region can cause trismus.


Inflammation of soft tissue around impacted third molar is the most common cause of trismus, and is a frequent sequel to surgical removal of mandibular third molars.


Pericoronitis usually resolves on its own in 10–14 days.


Treatment requires treating the underlying condition:  dental treatments, speech therapy for swallowing difficulty and mouth opening restrictions, physical therapy, and passive range of motion devices, pain medications (NSAIDs), muscle relaxants, and warm compresses may be used.


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