Overview 

Trismus or lockjaw refers to the restricted opening of the mouth, usually due to sustained, tonic spasm of jaw muscles. Earlier, the term "lock jaw" was used to describe tetanus, a bacterial infection that reduces mouth opening or causes difficulty in jaw movements. However, the term is now used regardless of its aetiology. It is usually associated with pain and restricts routine activity like speaking, eating and even the inability to maintain proper oral hygiene.² There are many causes of trismus, like dental surgery or removal of teeth, trauma to the mandible or even the face, as a consequence of temporomandibular disorders, as a part of dental infection, radiation therapy, inflammatory disorders and as a part of malignancy. Trismus can be temporary and can usually last for 2 weeks, or it can be chronic.³ Temporomandibular joint disorders (TMD) are a group of diseases that affect the temporomandibular joint (TMJ) and the muscles associated with it. These disorders often cause pain and dysfunction of the muscles that help in the movement of the jaw. Some important TMDs are myofascial pain dysfunction syndrome, osteoarthritis, and rheumatoid arthritis. These conditions can reduce the quality of life due to constant pain and headaches.⁴ 

The frequency of people affected with TMD based on geographical distribution is higher in South America (47%), Asia (33%) and Europe (29%).⁵ Is there any relationship between TMD and trismus? The answer is yes, and most of the individuals who have TMD complain of trismus. TMD may cause facial pain, a clicking sound from TMJ and also limited mandibular movement.³ So we should distinguish the cause of trismus, and if it is related to TMD, then early intervention could be made and improve the quality of life.

Pathophysiology of TMD-induced trismus 

Mouth opening is a result of the combined action of muscles, the TMJ movement that is the combined effect of the action of the condyle and coronoid and also a complex mechanism of muscular and neural activity. It is mainly divided into arthrogenous (intraarticular) and myogenous causes (extraarticular). Arthrogenous causes related to TMJ and it is mainly due to problems in the articular disc, osteoarthritis, and rheumatoid arthritis, and these can restrict the mouth opening. In the TMJ, there is a mandibular fossa, condyle and an articular disc (Figures 1 and 2). If the relation of the disc and joint changes or if the disc is thinned, it can lead to restricted mouth opening. TMDs related to myogenic pain include myositis, muscle spasm, and muscle contracture that affect the masticatory muscle, and this can also lead to lockjaw. Mainly masseter and temporalis are affected.⁶ It has a classic triad of symptoms: pain, a functional clicking sound in the TMJ, and reduced movement of the mandible.

Clinical presentation and diagnosis

There are many clinical presentations, and it is based on the type of TMD, whether it is intra-articular or extra-articular. Symptoms include: 

• Pain in the joints or in the associated muscles
• Trismus is an important finding
• Pain related to orofacial structures such as the ear, headache, etc. 
• Movement of the jaw is restricted forward as well as sideways movement, clicking or popping sound from the TMJ
• A ringing sound in the ear can even cause dizziness. 

Pain is an important finding which leads to a physician's visit. A thorough medical and dental history should be taken. Preliminary mode of examination is always the clinical examination, then diagnostic methods such as plain radiograph, CBCT, CT, MRI, and also USG are used. These would narrow down the cause of the symptoms, and appropriate treatment should be initiated.⁷

Examining trismus is based on the mouth opening, and normal is between 40-60c cm, that is 2-3 finger finger breadth. If the mouth opening is less than 35mm or 2 finger breath, then it is considered trismus. It can slightly vary among people based on gender and people.⁸ The individuals with trismus may have symptoms like: 

• Muscle getting tight (spasm)
• Difficulty to yawn
• Difficulty speaking and chewing 

Differential diagnosis

Care should be taken while diagnosing trismus related to TMD, as numerous other causes can give similar symptoms.

• Dental abscess or any dental infection
• Trauma or dislocation of the condyle  
• Some conditions may cause hyperactivity of muscles, like jaw clenching, bruxism, etc
• Nerve disorders like trigeminal neuralgia 
• Salivary gland disorders 

Proper history taking, clinical examination and diagnostic method help to arrive at a proper diagnosis.⁹

Management strategies 

Management of trismus should be based on the aetiology and usually focuses on the treatment of symptoms. Pain is the main symptom that hampers the quality of life. It can be improved by heat therapy, painkillers (NSAIDs), and muscle relaxants. Applying heat to the affected area can improve pain. It can be repeated every 15 to 20 minutes per hour.⁸ Painkillers are effective against pain, and it is more effective when combined with a muscle relaxant, which will loosen the stiff muscles. Restricted TMJ use should be advised; a soft diet and forced opening of the mouth should not be done. Frivolous dental treatment shouldn’t be carried out, as most of the treatment can cause a wide opening of the mouth. 

If the trismus is due to post-surgery, stretching exercise can be carried out by slowly and gradually increasing the mouth opening. Physiotherapy can also be carried out based on the aetiology and severity of the disease. Occlusal splints can be used in some cases of TMDs. Some TMDs are treated by means of semi-invasive procedures. Injecting steroids, hyaluronic acid and even Botox injection into the articular space in extreme conditions.¹⁰ Arthroscopy and arthrocentesis are also used. Severe forms of TMDs are treated by open surgery. Mostly, a conservative approach is done, and based on the severity, semi-invasive and surgical methods are used.⁶

Prognosis and long-term outcomes

Trismus is usually temporary and transient usually cures in a few days. If the aetiology or cause is like a severe form of TMDs, then the duration of cure will depend on the root cause. About 40% reported a remission without treatment, and most of the TMDS responded well to the conservative treatment.¹¹ If not treated, then it may lead to constant pain, difficulty speaking, eating and even yarn.

FAQs

What is the difference between trismus and tetanus?

Tetanus is a bacterial disease that affects the nerves, more precisely, neurotransmitters, which cause spasm of the muscles. The first symptom of spasm is seen in the jaw, and then it can spread to various other parts of the body. On the other hand, trismus can have multiple reasons, like dental extraction, surgery, malignancy, etc.

What if we do not treat TMDs at an early stage?

If the symptoms are minimal, usually people ignore them, and it can lead to tension building up around the jaw and muscles. It may eventually lead to severe pain, a clicking sound, and may even damage the teeth.

What is the 3-finger test in trismus?

Insert 3 fingers vertically inside the mouth, and if the fingers fit in between the upper and lower teeth, then the mouth opening is adequate. If it is 2 fingers or fewer, then it is said to reduce mouth opening. Usually, this test is performed in trismus.

What is the easiest way to treat trismus?

The treatment is usually based on aetiology and heat application, and NSAIDs are commonly used. In some cases, physiotherapy is also prescribed.

Can trismus be a sign of malignancy?

Yes, very rarely it can be a sign of malignancy, severe reduced mouth opening, and signs of lymphadenopathy. Radiographic findings can usually rule out malignancy

Summary 

Trismus is not a life-threatening situation, and most of the time it is temporary and early intervention can speed up the recovery. One of the most common aetiologies of trismus is TMDs, so in this case, both should be treated simultaneously. Pain is the most common symptom which can lead to poor quality of life and cause people to seek medical intervention. The diagnosis is mostly made by medical history, clinical examination and using diagnostic methods. Treatment depends severity of the condition. Initially, conservative methods are used, then complex, partially invasive and surgery is carried out in severe conditions. Trismus due to tetanus is a life-threatening condition and should be differentiated to arrive at the correct diagnosis. Trismus can be related to TMDs is possible in this modern era with the advent of the most sophisticated medical technology. So it is always better to get an early intervention for the treatment of trismus.