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Continuing Education Activity

Trismus is commonly referred to as lockjaw and is usually due to sustained tetanic spasm of the muscles of mastication. Although it was initially described in the setting of tetanus, it is now used to refer to a bilateral restriction in mouth opening from any cause. Although unilateral restriction may occur, trismus is a bilateral process resulting from increased muscle tone mediated by the efferent portion of the reflex arch of the trigeminal nerve. This activity reviews the evaluation and management of trismus and highlights the role of interprofessional team members in collaborating to provide well-coordinated care and enhance patient outcomes.


  • Describe the pathophysiology of trismus.
  • Review the presentation of trismus.
  • Summarize the treatment options for trismus.
  • Outline the importance of enhancing care coordination among the interprofessional team to ensure proper evaluation and management of trismus.


Trismus refers to the restriction of the range of motion of the jaws. Commonly referred to as "lockjaw," trismus typically stems from a sustained, tetanic spasm of the mastication muscles. Initially described in the setting of tetanus, it currently refers to restricted mouth opening due to any etiology. Although unilateral restriction may occur, by definition, trismus is a bilateral process that results from increased tone mediated by the efferent portion of the reflex arch of the trigeminal nerve.

Trismus is usually temporary and typically resolves in less than two weeks, but permanent trismus may also occur, interfering with everyday activities such as speaking, eating, and even swallowing.[1][2]


Multiple conditions can result in trismus. Some authors classify trismus according to the involvement of the temporomandibular junction (TMJ) in intraarticular and extraarticular etiologies.[2] Others have outlined the causes into broad categories such as infectious, traumatic, and neoplastic sources.[1] Trismus may also be iatrogenic, resulting from prescribed interventions and treatments. Below are some of the conditions associated with trismus:


  • Hemarthrosis/hematoma
  • Fracture or dislocation of the mandible or zygomatic arch
  • Temporomandibular joint (TMJ) contusion
  • Intraarticular bone islands/foreign bodies
  • Displaced meniscus
  • Direct injury to muscles of mastication


  • Osteoarthritis
  • Soft tissue fibrosis
  • TMJ ankylosis
  • Rheumatoid arthritis
  • Scleroderma
  • Temporal arteritis


  • Pyogenic arthritis
  • Osteomyelitis of the mandible
  • Tonsillitis
  • Peritonsillar or other pharyngeal abscesses
  • Tetanus
  • Odontogenic abscess
  • Mumps
  • Parotid abscess

Congenital Malformations

  • Pierre-Robin sequence[3]           
  • Trismus-pseudocamptodactyly syndrome

Head and Neck Neoplasms

  • Pharyngeal carcinoma
  • Parotid gland tumors


  • Impacted third molar (or following extraction thereof)


  • Perioperative inflammation
  • Radiotherapy for head and neck cancer


  • Tetanus
  • Status epilepticus
  • Parkinsonism
  • Strychnine, phenothiazine poisoning
  • Medication adverse effect (phenothiazines, metoclopramide, tricyclic antidepressants)
  • Hypocalcemia, hypomagnesemia, respiratory alkalosis

Psychogenic (conversion disorder)


The prevalence of trismus ranges widely, partly because no clear criteria have been established. Normal jaw opening is greater than 30 to 40 mm. Trismus has been defined as a mouth opening less than 40 mm; others have described it as an opening to 15 to 30 mm, or even less than 20mm. Additionally, some authors have graded trismus according to visual assessment of mouth opening (light/moderate/severe or grades 1 to 3, again corresponding to mouth opening). Its incidence is vastly variable and dependent on the inciting etiology. Importantly, trismus is a common finding in certain patient populations, such as those with congenital micrognathia syndromes or undergoing radiation therapy for head and neck cancers.[3][4] It can also be a relatively rare complication of common conditions, such as pharyngitis.


The muscles responsible for mouth closure, namely the masseter, temporalis, and medial pterygoid muscles, exert a force 10 times greater than the muscles that open the mouth, including the lateral pterygoid, digastric, and hyoid muscles. Innervation for the majority of these muscles is provided by the mandibular division of the fifth cranial nerve. The muscle groups that control jaw opening and closure act in antagonism, as neurogenic stimulation of one group causes reflex neural inhibition of the other. While the inciting insult may be unilateral, the reflex activated is bilateral.

Trismus and Head and Cancer

Trismus is a common side effect of head and neck cancer and its treatment.[5] According to recent studies, it develops in 38% to 42% of head and neck cancer patients.[6][7]The temporomandibular joint or the mastication muscles can experience fibrosis because of radiotherapy, leading to trismus.[5] The risk of trismus goes up when the medial pterygoid muscle is in the radiation zone.[8] Furthermore, surgical procedures to treat head and neck cancer can scar the mastication muscles, developing the undesired restricted mouth opening.[9]

History and Physical

The normal mouth opening ranges between 40 to 60 cm (two to three finger breadths), and many authors consider a maximum mouth opening of less than 35 mm trismus.[1] However, it varies from individual to individual, and even according to sex, males generally feature a wider mouth opening.[1]

Patients presenting with trismus will note a restricted mouth opening and sometimes pain when attempting to open the mouth. However, patients often have complaints related to the causative condition rather than the resulting trismus. Those with odontogenic etiologies may complain of tooth or gum pain and swelling; patients with traumatic causes may note facial or mandibular pain. A complete clinical examination should be performed to identify systemic causes. Fever may indicate an infectious source; weight loss may be notable among patients with neoplastic causes; carpopedal spasms and paresthesias may accompany trismus in patients with neurogenic or metabolic causes. A history of tobacco use or known cancer could raise suspicion of a neoplastic cause.[1]

More commonly, trismus is a physical exam finding encountered on attempts to visualize the oral and pharyngeal structures via mouth opening. This challenges the examining clinician's attempt to ascertain the cause of trismus. As much as possible, the exam should be targeted to the teeth and gums; facial bones and TMJ; pharyngeal pillars, tonsils, uvula; and the neck.

Assessment of the patient's speech may be necessary; some pharyngeal infections implicated in trismus may also cause changes in the patient's voice; a "hot potato voice" may be associated with tonsillitis or peritonsillar abscess. A directed neurologic exam should be performed to evaluate for neurogenic causes.[2]


The diagnosis of trismus is clinical. Imaging adjuncts may be useful to determine its etiology and determine the articular involvement of the TMJ. Computed tomography can help to identify traumatic etiologies, including hematomas or facial and mandibular fractures. Magnetic resonance imaging may identify space-occupying lesions or abnormalities in the pharyngeal or oral structures.

Treatment / Management

Treatment of trismus is directed at the inciting etiology and is most commonly treated symptomatically. Symptom-directed interventions, including heat therapy, analgesics such as non-steroidal anti-inflammatory agents, and muscle relaxants, are usually prescribed in the acute phase and have been described as mainstays for treating uncomplicated transient trismus. Heat therapy includes applying moist hot towels for 15 to 20 min per hour.[1] When it comes to analgesics, aspirin is usually sufficient.[1] When a muscle relaxant is needed, a benzodiazepine, such as diazepam, is recommended: 2.5 to 5 mg three times per day.[1] The clinician should also encourage a soft diet for the duration of the pathology.[1]

Further dental treatment must be avoided until trismus resolves [10] - usually within 48 hr of initiating therapy.

Stretching exercises are indicated after the acute phase or in patients with post-traumatic and post-operative trismus, particularly when persisting longer than one week. The exercises typically consist of repeated attempts to open the mouth against applied resistance, usually divided into multiple sessions per day.[5] Physiotherapy includes opening and closing the mouth and lateral movements for 5 min every 3 to 4 hr.[11] Sugar-free chewing gum can be indicated to stimulate lateral movements.[1]

Trismus may become chronic in the setting of fibrosis or ongoing radiotherapy; these cases may benefit from intensive physiotherapy, sometimes utilizing commercially available jaw motion rehabilitation devices or microcurrent therapy, particularly in patients refractory to more conservative approaches. Some authors have also described treatment with xanthine derivatives such as pentoxifylline.[1][12]

If the opening limitation does not improve after 2 to 3 days, or in cases of extreme trismus, refer to an oral and maxillofacial surgeon.[1]

Extreme trismus cases that are repeatedly refractory to treatment require surgical procedures, like reducing the mandibular height to achieve a larger mouth opening, coronoidectomy, or tissue release and free flap reconstruction.[5]

Trismus Treatment Summary

Acute Phase After Acute Phase Surgical Treatment of Refractory Trismus

Heat Therapy

Moist hot towels


Mouth opening and lateral movements

Reducing the height of the mandible


NSAIDs, such as aspirin.

Chewing gum for lateral movements Tissue release and free flap reconstruction

Muscle Relaxation

Benzodiazepine, such as diazepam

Physiotherapy with commercially available devices Coronoidectomy
Soft Diet    

Differential Diagnosis

Since trismus has been defined as a restriction in mouth opening regardless of etiology, it does not have a wide differential diagnosis. Some authors have argued that "true trismus" is mediated via the trigeminal nerve, and intraarticular causes of impaired mouth opening, such as TMJ ankylosis or fibrosis, should be considered separately.[1] Others have outlined such intraarticular processes as subclassifications of trismus.[12]


Trismus is most commonly self-limited and transient, typically resolving within two weeks. When identified in certain patient populations, e.g., in patients who develop fibrosis from radiotherapy, the course of trismus may be longer and more refractory to conservative treatment.[4]


Trismus interferes with speaking, eating, and swallowing; it has been associated with aspiration due to impaired swallowing mechanisms. Intubation via the oropharyngeal route may be impossible in patients with significant trismus, necessitating other approaches such as nasopharyngeal intubation or tracheotomy. When its duration is prolonged, leads to fibrosis of the TMJ, necessitating directed therapy.[12]


Consultation may be considered based on the suspected etiology. Dental or oral surgery care may be enlisted for odontogenic causes, while an otolaryngologist is at times consulted for drainage of a peritonsillar abscess. Physiatrists may also be involved in a patient's care when directed therapeutic interventions are necessary to treat refractory trismus.[1]

Deterrence and Patient Education

Patients should receive counsel to rest their jaw, avoid activities like nail-biting, clench of teeth, and potentially work with a physical therapist on jaw muscle strengthening in acute cases.

Pearls and Other Issues

  • Trismus most commonly occurs in the setting of uncomplicated common conditions (e.g., wisdom tooth extraction); it may also be a relatively common complication of uncommon diseases (fibrosis following head and neck radiotherapy).
  • Trismus is best addressed by identifying the inciting etiology and directing treatment to the underlying cause.
  • Most cases of trismus resolve following symptom-directed treatment with heat therapy and NSAIDs.
  • Refractory chronic trismus may require physiotherapeutic interventions.

Enhancing Healthcare Team Outcomes

Due to the wide variety of trismus etiology, the condition is best managed by an interprofessional team. Consultation may be considered based on the suspected etiology. Dental or oral surgery care may be enlisted for odontogenic causes, while an otolaryngologist is at times consulted for drainage of a peritonsillar abscess. Physiatrists may also be involved in a patient's care when directed therapeutic interventions are necessary to treat refractory trismus.[1] The outcomes are good in most patients if the primary cause can be treated. However, in patients with severe trauma, scarring, and radiation therapy, trismus may be chronic and lead to poor quality of life.[13][14][15][16] [Level 5]

Article Details

Article Author

Livia Santiago-Rosado

Article Editor:

Cheryl Lewison


11/24/2021 7:08:11 AM

PubMed Link:




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