Locked Jaw (Trismus): Causes, Symptoms and Treatment
Waking up and finding that your mouth will not open properly can be unsettling. Locked jaw, known clinically as trismus, describes a reduced ability to open the jaw, and it can come from several different causes. This guide explains lock jaw causes and treatment in plain language, including common symptoms, what the research says about jaw exercises and manual therapy, ways to reduce jaw locking, and when to seek urgent care.
When trismus is related to jaw muscle tension or temporomandibular joint (TMJ) dysfunction, physiotherapy may help improve jaw movement and manage discomfort, depending on the underlying cause. Treatment may involve carefully selected jaw exercises, movement guidance, and manual therapy where appropriate. For people experiencing ongoing jaw stiffness or restricted movement in Balmain and across Sydney, Sydney TMJ Physio provides a service focused on TMJ-related concerns and jaw function. A professional assessment can help determine whether physiotherapy is suitable or whether another type of medical or dental care is needed, particularly when symptoms develop suddenly or worsen.
What Is Locked Jaw (Trismus)?
Trismus is the clinical term for restricted mouth opening. In the research literature it is commonly defined as a maximum mouth opening of 35 millimetres or less, measured between the upper and lower front teeth. Many people use the word lockjaw as a general label, but a locked jaw can mean different things: a jaw that feels stiff and will not open fully, a jaw that catches or clicks during movement, or a jaw that becomes stuck in one position.
Your jaw joint (the temporomandibular joint, or TMJ) and the chewing muscles work as a team, so a problem in either one can limit movement. Pain, muscle guarding, joint disc changes, swelling and scar tissue can all play a part. This is why a proper assessment matters before choosing any locked jaw treatment.
What Are the Common Locked Jaw Causes?
Clinical references describe trismus as multifactorial, meaning more than one mechanism can be involved at the same time. Causes are often grouped into those that involve the joint itself and those that involve the muscles and soft tissues around it. Short-lived trismus after a dental procedure or an injection into the jaw muscles tends to settle by itself, while long-standing trismus usually needs a closer look at the underlying cause.
Temporomandibular disorders (TMD)
Temporomandibular disorders are a common reason for a stiff or locked jaw. Overworked chewing muscles, habits such as clenching or grinding, and changes to the small disc that cushions the joint can all limit how far the mouth opens. When the disc becomes displaced and does not move back into position, the jaw may feel blocked, which is often called a closed lock.
Jaw injury, dental work and infection
A blow to the face, a fall, wisdom tooth removal or an injection near the jaw muscles can lead to pain, swelling and protective muscle tightening that restrict opening. Infections in or near the jaw can also limit movement, and these usually come with other signs such as fever, swelling or a bad taste in the mouth. They need prompt medical or dental care.
Cancer treatment and other medical conditions
Trismus is a recognised complication for some people treated for head and neck cancer. Radiation-related fibrosis, which is a stiffening of muscle and soft tissue, is considered the most frequent cause in this group, and surgery can add scarring. Estimates of how many people are affected vary widely between studies. Connective tissue conditions and, rarely, infections such as tetanus can also cause trismus.
Locked Jaw Symptoms to Look Out For
Locked jaw symptoms differ from person to person and depend on the cause. Common features include:
Difficulty opening your mouth wide enough to eat, yawn, speak or brush your teeth
Jaw stiffness, often worse in the morning or after prolonged chewing
Pain around the jaw, cheek, temple or ear
Clicking, catching or a sensation that the jaw is blocked
The jaw drifting to one side when you open
Tension headaches or tiredness in the chewing muscles
How Do You Cure a Locked Jaw?
The honest answer is that it depends on why the jaw is limited. Many cases linked to muscle overuse or irritation improve with conservative care, while others need medical or dental management alongside rehabilitation. No treatment can promise a particular result, so the goal is a clear diagnosis, a sensible plan and steady progress toward comfortable, functional jaw movement.
Start with an accurate assessment
A physiotherapist will usually measure how far you can open, check how the jaw moves, assess the joint and chewing muscles, and look at the neck and posture. They will also ask about injuries, dental work, medical history and stress levels. If something about your presentation suggests a cause outside the jaw, you will be referred on to your doctor or dentist.
Jaw exercises and gentle stretching
Exercise is the best-supported conservative approach for trismus. A systematic review has examined exercise therapy for trismus after head and neck cancer, and a 2025 scoping review of randomised trials found that exercise was the most studied rehabilitation option. The same review noted that the reasons why exercise helps are not yet well explained, and that results varied between trials. In practice, exercises should be individualised, started at a comfortable level and progressed gradually. Forcing the jaw open is not recommended.
Manual therapy and physiotherapy
Hands-on treatment aims to ease tight muscles and improve how the jaw and neck move together. Manual therapy for temporomandibular disorders has been reviewed in a systematic review and meta-analysis that looked at pain and maximum mouth opening over the medium and long term. Some randomised trials in people with head and neck cancer have also reported better mouth opening after manual therapy, although the mechanisms are still being studied. Physiotherapy usually combines education, manual techniques, exercises and habit changes rather than relying on one method.
When medical or dental input is needed
Some situations call for care beyond physiotherapy, such as infection, a jaw that is dislocated, or trismus linked to a tumour or a previous course of radiotherapy. Your dentist or doctor may suggest a bite splint, medication or imaging, and your physiotherapist can work alongside them so your care stays coordinated.
Locked Jaw Myths and What the Evidence Supports
Searching for lockjaw causes remedies online turns up plenty of confident advice. Here are some common myths compared with what the evidence supports:
Myth: Lockjaw always means tetanus. Evidence: Tetanus is a rare cause. Most locked jaw cases involve the jaw muscles or joint, although a stiff jaw with muscle spasms after a deep wound needs urgent medical attention.
Myth: Forcing your mouth open will break the stiffness. Evidence: Aggressive stretching can irritate the joint and muscles. Gradual, pain-aware movement is the safer approach.
Myth: Clicking always means a locked jaw is coming. Evidence: Many people have painless jaw clicking that never causes problems.
Myth: A mouthguard fixes every jaw problem. Evidence: Splints suit some people, but they are one option among several and work best as part of a broader plan.
Myth: Rest alone will always sort it out. Evidence: Short-term rest can help flare-ups, but a jaw that stays restricted usually needs assessment and active rehabilitation.
How to Stop Jaw Locking?
The most useful approach is to reduce the load on the jaw while keeping it moving within a comfortable range. This is the same thinking behind most jaw stiffness treatment: calm the irritated tissues first, then restore movement and address the habits that keep triggering symptoms.
If your jaw has locked recently and you have no warning signs, these simple steps are commonly recommended while you arrange an assessment:
Choose softer foods for a short period and cut food into small pieces
Avoid chewing gum, very chewy foods and wide bites
Support your chin with your hand when you yawn so you do not open too wide
Try a warm compress over the cheek and jaw muscles to ease tension
Rest your tongue gently on the roof of your mouth with lips together and teeth slightly apart
Reduce habits such as nail biting, pen chewing and daytime clenching
Look at stress, sleep and neck posture, which often influence jaw muscle tension
Why a personalised plan matters
Two people with the same stiff jaw can need very different advice. One may need to ease muscle overload, while another needs help with a displaced disc or a long-standing restriction after surgery. An individualised plan focuses on long-term function, not only short-term relief, and helps reduce the chance of the problem returning.
When Should I Worry About Lockjaw?
Most jaw stiffness is not dangerous, but some signs should not be ignored. Seek urgent medical care or go to your nearest emergency department if any of the following apply:
Your jaw is stuck open or stuck closed and you cannot free it
The jaw locked after a significant fall, blow or suspected fracture
You have fever, facial or neck swelling, or a bad taste suggesting infection
You have trouble swallowing or breathing
You have muscle spasms or stiffness in the neck or body, especially after a deep or dirty wound
Book a prompt assessment with your doctor, dentist or physiotherapist if your mouth opening is getting smaller over time without a clear reason, if you have a history of head or neck cancer or radiotherapy, or if the problem lasts more than a week or two, keeps returning, or affects eating, speaking or sleep. In Australia, call 000 in an emergency. Our clinic is a physiotherapy practice and not an emergency or hospital service.
TMJ Physiotherapy for Locked Jaw in Balmain
At our Balmain clinic, our physiotherapists assess how your jaw, neck and chewing muscles are working together and build an individualised, goal-oriented plan around your findings. Our approach is evidence-based and focuses on long-term function, with rehabilitation, prevention and education working together.
If you are unsure whether your jaw problem needs physiotherapy, dental care or medical review, an initial assessment is a good place to start. We will explain what we find, discuss your options in plain language and coordinate with your dentist or doctor when needed.
📅 Book a jaw pain physiotherapy session with Sydney TMJ Physiotherapy in Balmain and get a treatment plan tailored to your needs.
References
Anarte-Lazo, E., Bravo-Vazquez, A., Bernal-Utrera, C., Torres-Lagares, D., Falla, D., & Rodríguez-Blanco, C. (2025). The rationale and explanation for rehabilitation interventions in the management of treatment-induced trismus in people with head and neck cancer: A scoping review of randomized controlled trials. Medicina, 61(8), 1392. https://pmc.ncbi.nlm.nih.gov/articles/PMC12388229
Trismus. (n.d.). In StatPearls. StatPearls Publishing. NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK493203/
Herrera-Valencia, A., Ruiz-Muñoz, M., Martin-Martin, J., Cuesta-Vargas, A., & González-Sánchez, M. (2020). Efficacy of manual therapy in temporomandibular joint disorders and its medium- and long-term effects on pain and maximum mouth opening: A systematic review and meta-analysis. Journal of Clinical Medicine, 9(11), 3404. https://pmc.ncbi.nlm.nih.gov/articles/PMC7690916/
Kamstra, J. I., van Leeuwen, M., Roodenburg, J. L. N., & Dijkstra, P. U. (2017). Exercise therapy for trismus secondary to head and neck cancer: A systematic review. Head & Neck, 39(1), 160-169. https://doi.org/10.1002/hed.24366
Dijkstra, P. U., Huisman, P. M., & Roodenburg, J. L. N. (2006). Criteria for trismus in head and neck oncology. International Journal of Oral and Maxillofacial Surgery, 35, 337-342. https://doi.org/10.1016/j.ijom.2005.08.001
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