Can't Open Your Mouth Fully? Jaw Lock From a Dental Abscess

If you have toothache and you have also noticed that your mouth will not open as wide as usual, those two things are almost certainly connected — and the connection is one that clinicians take seriously.

Restricted jaw opening is called trismus. When it accompanies a dental infection, it indicates that the infection is no longer confined to the tooth and the bone immediately around it. It has reached the soft tissue spaces containing the muscles that open and close your jaw, and those muscles have gone into protective spasm.

That is a meaningful escalation, and it changes the timescale on which you need to be seen.

The muscles that move the jaw do not sit in isolation. They occupy defined fascial spaces, and several of those spaces are immediately adjacent to the roots of the back teeth — particularly the lower molars, and most particularly the wisdom teeth.

The medial pterygoid muscle lies in the pterygomandibular space, on the inner side of the lower jaw. The masseter lies in the submasseteric space on the outer side. Infection spreading from a lower molar root can track into either. Once inflammatory exudate reaches the muscle, the muscle responds with sustained reflex contraction — a protective splinting response that limits movement in order to limit pain.

The result is a jaw that will not open. Not because the joint is damaged, but because the muscle that would allow it to open is inflamed and in spasm.

This is why trismus is treated as a marker of spread rather than as a symptom in its own right. The infection had to reach the muscle space to produce it.

Normal maximum opening for an adult is roughly 40 to 55 millimetres — around three of your own fingers stacked vertically between the front teeth. Clinicians use the reduction from that baseline as a rough index of severity:

• Mild restriction — around 30 to 40 mm, or roughly two and a half fingers.

• Moderate restriction — around 20 to 30 mm, two fingers or fewer.

• Severe restriction — under 20 mm, where a finger or two barely fits.

The trend matters as much as the number. Opening that is reducing hour by hour indicates an infection that is actively progressing. It is worth measuring your own opening and noting the time, because a clear account of how it has changed is genuinely useful information for whoever assesses you.

Severe restriction also has a practical implication: it makes examination, imaging and treatment more difficult, and it can make airway management more complex. That is part of why it raises urgency.

Contact emergency services or attend an emergency department immediately if any of the following are present:

• Difficulty breathing, or breathing that feels noisy or effortful.

• Difficulty swallowing, drooling, or an inability to manage your own saliva.

• Swelling under the jaw or in the floor of the mouth, particularly if the tongue feels raised or pushed up.

• Swelling spreading towards the neck or up towards the eye.

• Fever with facial swelling, rigors, or feeling systemically unwell.

• A change in your voice, particularly a muffled or "hot potato" quality.

• Rapidly reducing jaw opening over hours.

These indicate infection involving deep spaces of the neck. Ludwig's angina — bilateral involvement of the submandibular, sublingual and submental spaces — is a recognised airway emergency arising from lower molar infections. It is uncommon, and it is why this list exists. Our articles on when a toothache infection may be spreading and can a tooth abscess be life-threatening cover this in more detail.

Trismus with toothache but without any of the above still needs same-day or next-day dental assessment. It is urgent, not routine.

Not every locked jaw is infective, and it is worth knowing the alternatives.

Pericoronitis is inflammation of the gum flap over a partially erupted wisdom tooth. It is extremely common in the late teens and twenties, frequently causes trismus, and sits on a spectrum with frank abscess formation. It needs assessment, and our wisdom teeth page covers management.

Temporomandibular joint disc displacement without reduction — closed lock — restricts opening mechanically. The distinguishing features are that it usually has no swelling, no fever and no toothache, often has a history of clicking that stopped when the restriction began, and typically limits opening to around 25 to 30 mm with deviation towards the affected side.

Muscle spasm from clenching can restrict opening, usually with generalised muscle tenderness and no infective signs.

After a dental injection, particularly an inferior alveolar nerve block, trismus can follow needle trauma or a small haematoma in the medial pterygoid. This typically appears a day or two later and settles over days to weeks.

After wisdom tooth removal, some restriction is expected from swelling and muscle irritation, improving over the first week. Restriction that worsens after day three, especially with a foul taste, may indicate infection or a dry socket.

Rarer causes include trauma to the jaw, tetanus, radiotherapy fibrosis, and tumours affecting the muscle spaces. These are uncommon but are reasons why persistent unexplained trismus is investigated rather than observed indefinitely.

Distinguishing an abscess from other sources of pain is discussed in telling the difference between toothache and an abscess.

Assessment covers the extent of swelling, the degree of opening, temperature, and whether the swelling is firm or fluctuant. A radiograph identifies the causative tooth where opening allows it to be taken — and where it does not, that limitation itself contributes to the decision about where you should be treated.

Management follows a clear principle: the source has to be dealt with, and any collection has to be drained. Antibiotics alone do not resolve a dental abscess, because there is little or no blood supply within a necrotic root canal for an antibiotic to reach, and a walled-off collection of pus is poorly penetrated. Antibiotics have a role in spreading infection and in systemically unwell patients, but as an adjunct. This is set out in can antibiotics replace root canal treatment.

Definitive treatment means either root canal treatment to remove the infected pulp and disinfect the canal system, or extraction of the tooth. Where trismus makes immediate treatment impossible, infection is controlled first and definitive treatment follows once opening improves.

Where there is significant swelling, systemic involvement or airway concern, referral to a maxillofacial unit for drainage under general anaesthetic is appropriate.

• Take over-the-counter pain relief according to the packet instructions and any advice from your pharmacist.

• Warm salt water rinses may help locally, though gently — do not attempt to force your mouth open.

• Do not apply heat to the outside of the face. External heat can encourage infection to spread through the soft tissues.

• Do not attempt to drain it yourself.

• Soft diet, adequate fluids. Dehydration makes everything harder.

• Sleep propped up if swelling is present.

• Monitor your opening and your temperature, and note the trend.

• Do not wait it out. If an abscess drains spontaneously and the pain eases, the source remains and it will recur. Bad taste from a ruptured abscess explains why that relief is misleading.

How long does jaw lock from an abscess last?

It improves as the infection is controlled, typically over several days once the source is treated. It does not resolve reliably while the causative tooth remains untreated.

Can I just take antibiotics and wait?

Antibiotics may reduce spread temporarily but do not remove the source. The infection recurs, often more extensively, and repeated courses contribute to antibiotic resistance.

Is it definitely an abscess if I cannot open my mouth?

No. Joint problems, muscle spasm, pericoronitis and post-injection trismus all restrict opening. The combination of restriction with toothache, swelling or fever points strongly towards infection.

Should I go to A&E?

Yes, if there is difficulty breathing or swallowing, spreading swelling, fever with facial swelling, or a change in your voice. Otherwise contact a dentist for same-day assessment.

Why does it affect wisdom teeth so often?

Lower wisdom teeth sit immediately adjacent to the pterygomandibular and submasseteric spaces, and they are frequently partially erupted, which allows bacteria beneath a gum flap that cannot be cleaned effectively.

Restricted jaw opening with dental pain should be assessed the same day. It is the type of problem that resolves readily when addressed early and becomes considerably more involved when it is not.

You can contact our team at our Wimpole Street practice, or see our emergency dentist page for urgent care.

This article provides general information about restricted jaw opening associated with dental infection and does not constitute individual dental advice. Dental infections can spread rapidly and some presentations are medical emergencies. If you have difficulty breathing or swallowing, swelling in the floor of the mouth or neck, or fever with facial swelling, seek emergency medical care immediately rather than waiting for a dental appointment. Wimpole Dental is regulated by the Care Quality Commission, and our clinicians are registered with the General Dental Council.

Next review due: 17 September 2027