Overview

Trismus is a condition that causes painful spasms in the muscles that surround the jaw joints.¹

In the past, lockjaw has been used as a synonym for both trismus & tetanus.

Trismus is derived from the Greek word trismos, meaning ‘’spasm, a grinding, rasping, or gnashing.

When your jaw muscles are so tight that you can’t open your mouth, and experience difficulty opening your mouth.

Trismus refers to the restricted mouth opening due to any aetiology. It is usually temporary and typically resolves in less than 2 weeks. Still, permanent trismus may also occur, interfering with everyday activities such as speaking, eating, and swallowing. Trismus can impair a patient’s quality of life, by causing pain, difficulty in mastication, subsequent nutrition, maintenance of good oral hygiene, receiving dental treatment & speech, long-lasting will cause depression.

Health care providers diagnose trismus by asking about symptoms & examining the jaw, neck, and temporomandibular joint.

Normal mouth opening measures about 40 to 60 mm, but if you have a trismus, you may not be able to open your mouth wider than 20 to 35mm. Trismus can be a red flag for early signs of oral malignancy. A simple checklist can help to identify patients who are at risk.² Read more to learn about the occurrence of trismus after oral and maxillofacial surgery.

Why does trismus happen after surgery?

Multiple agents are causing trismus. Acute trismus is caused by facial, mandibular or iatrogenic factors. Iatrogenic factors include surgical removal of wisdom teeth, intramuscular administration of local anaesthesia and its self-limiting nature.³

Chronic trismus is caused by severe trauma, temporomandibular joint disorder, radiotherapy followed by head & neck cancer surgery, and neoplasia.

Surgical factor

• Injury to jaw muscles: Trismus is a possible complication of the inferior alveolar nerve block. During this block, the muscle of mastication, especially the medial pterygoid, gets penetrated accidentally by a needle, causing pain related to the trismus. When the injured muscle gets stretched, it triggers pain, causing immediate reflex contraction and limited mandibular mouth opening⁴
• Intramuscular hematoma also causes trismus
• Injury to the nerve: injury to the inferior alveolar artery or vein leads to hematoma in the pterygomandibular space, resulting in trismus
• Short-term trismus occurs as a complication of the surgical extraction of lower wisdom teeth (mandibular third molar). These are the last molars on either side of the jaw. Trismus happens because people have to open their jaw wide for a long time during surgery
• Trauma to the face & mandible: mandibular fracture, rare fracture of zygomatic arch, zygomaticomaxillary complex can cause trismus as they impede the movement of the coronoid process
• Injury to the mandibular nerve during maxillofacial surgery

Non-surgical factor 

• Trismus is a sign of temporomandibular disorder(TMD): TMD refers to the pain and dysfunction of the mastication of the temporomandibular joint(TMJ) & the muscles. Myofascial pain & disc displacement without reduction are the 2 common types of TMD that cause trismus
• Trismus as a complication of dental infection: In patients with dental infection is suspected with trismus, masticatory muscle is involved. These infection gets spread into the head & neck region, resulting in life-threatening complications like mediastinitis & cervical cellulitis⁵
• From the dental infection, pericoronitis⁶ is mostly associated with trismus
• Fibrosis & scar tissue formation after the surgery: Trismus is a common side effect of head & neck cancer treatment. According to a recent study, 35 - 42% of head & neck cancer patients develop trismus. The TMJ or the masticatory muscle can experience fibrosis because of radiotherapy. Trismus risk increases when the pterygoid muscle is in the radiation zone
• Surgical procedures to treat head & neck cancer can cause scar formation in the masticatory muscle, leading to restricted mouth opening

How do you know it’s trismus?

The symptom that is most common is difficulty in opening the mouth fully. As this may limit their ability to eat solid types of foods and to have a sufficient amount of liquids to get adequate nutrition, so soft liquid diet is advised by their speech or swallowing therapist to improve their mouth opening.⁷

Other symptoms are pain in the jaw, difficulty chewing or swallowing, cramping of jaw muscles & surrounding areas and difficulty or discomfort with activities that need full jaw range of motion, like teeth brushing, yawning.

Diagnosis

A comprehensive diagnosis is essential for effective treatment.⁸ The diagnostic process typically involves

• Clinical examination: A healthcare provider performs a physical examination, assesses the range of motion in the jaw, and identifies muscle tightness & visible signs of infection or injury
  • 3 finger test: Functionally normal mouth opening can be assumed if the patient can fit 3 fingers side by side between the top & bottom incisors
  • < 4 cm interincisor gap¹⁵
• Imaging studies: X-ray, CT scan, and MRI scan are used. It helps to visualise jaw structure, identifying underlying abnormalities to cause trismus
• Laboratory tests: It is conducted when an infection is suspected, which may include a blood test or a culture report. It aims to identify the causative agents for the infection

Who is at risk?

Temporomandibular dysfunction(TMD) is common amongst head & neck cancer patients(HNC). Patients who suffer from pain in jaw muscles & pain in moving the jaw before the start of oncological treatments are at a higher risk of developing radiation-induced trismus after 6 months. clinician should strive to optimize the patient pain treatments & over all health before, during, after radiotherapy(RT).⁹

Trismus is developed more in the area of the mouth, showing lesions like as those in the buccal mucosa, maxilla.¹⁰

Radiotherapy is one of the main risk factors for the development of trismus. The primary factor in limiting jaw movements in irradiated patients is the formation of collagen secondary to radiation damage.

AFAB (assigned female at birth) individuals have been reported to have more trismus because of a smaller mouth opening than AMAB(assigned male at birth).¹¹

How is trismus treated?

 Passive stretching exercise:

• Keep your thumb fingers on the tip of the upper front teeth
• Put your index fingers on the other hand into the lower front tooth
• Then apply slight pressure on both sides to keep both jaw far apart, as there is no feeling of pain, stretch it for 5-10 seconds, relax, take one full breath, repeat 5 times 
• Keep good posture
• Massage your masseter muscles (cheek muscles) so they will improve muscle elasticity
• Therapeutic exercise: guided exercise¹⁴

 Medications 

• Anti-inflammatory drugs: NSAIDS like ibuprofen for pain & swelling
• Muscle relaxants: to reduce or mitigate muscle spasms
• Antibiotics: for treating infection
• Steroid injection: to reduce inflammation and muscle spasm.

Dental & surgical intervention

• To dental infections & abscesses
• Oral surgery: to repair structural damage, as in TMJ disorder, and also scar tissue removal

Advanced treatments

• Botox injection: Treating muscle spasms that may interfere with the mouth opening
• Electromyography: It is used to assess the degree of muscle activity within the joint¹⁶
• Radiation-induced trismus therapy: This therapy is specifically for cancer-causing trismus
• Therabite: It is a rehabilitation therapy device used to treat trismus¹⁶
• Dynasplint: Custom-made device used to improve mouth opening¹⁶

Lifestyle adjustments

• Consuming soft food can help release jaw strain
• Avoid habits like clenching or grinding of teeth

Can trismus be prevented?

To reduce the risk of developing trismus or worsening existing symptoms.

• Maintaining good oral hygiene: seeking proper brushing, dental flossing, and regular dental checkups
• Seek early treatment: Do necessary dental preventive measures, take professional guidance at the right time
• Use protective gear: Use protective helmets if required wear mouth guards
• Practice relaxation techniques: stress management to prevent clenching or grinding. Spend quality time with families to release the tension spike
• Follow post-surgical instructions: after the dental procedure, follow your dentist's recommendations to minimise complications
• Proper post-operative care: early mobilisation of the jaw, and a soft diet 

FAQs

What are the early signs of trismus?

Early signs include difficulty in opening the mouth fully, pain around the jaw, stiffness in the jaw muscles.

Can trismus go away on its own?

Mild cases may resolve with time & simple treatments like jaw exercise and anti-inflammatory medications. Severe or persistent requires professional care.

Can stress cause trismus?

Yes, stress can lead to jaw clenching or grinding, which can contribute to a locked jaw.

Are there home remedies for trismus?

Home remedies include gentle jaw stretching, warm compresses, and consuming soft foods to minimise strain. Always consult a healthcare professional before starting self-treatment. 

Summary

Trismus is common but treatable after oral surgeries. Early detection and care are key to a full recovery.

By maintaining good oral hygiene, seeking prompt medical care, and following preventive measures, you can reduce the risk of trismus and protect your oral health. It is usually as a result of muscle trauma after a head & neck cancer treatment that requires surgery or radiotherapy to the oral cavity, oropharynx, muscles of mastication & temporomandibular joint. After a dental surgery, having your wisdom tooth removed. Infection, Trauma, Painful mucositis, Fibrosis.

Trismus following oral & maxillofacial surgery is preventable with early intervention if the necessary cause is addressed early.