← All explanationsTrismus

Why will the mouth not open properly?

Trismus describes markedly restricted mouth opening. Possible causes involve muscles, the jaw joint, injury or infection, among other conditions. The term names the limitation, not its cause.

For dental trainees & teams

01 / 03

Movement is restricted

Eating, speaking and oral care may become difficult. It matters whether restriction began suddenly, is worsening or started after a procedure.

02 / 03

Do not force it open

Do not force the mouth wider. Examination and treatment depend on the cause; stretching exercises are not appropriate for every acute situation.

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Watch for warning signs

Arrange immediate help for fever, swelling, worsening restriction or major difficulty drinking. Breathing problems or swelling with difficulty swallowing are an emergency: call 112 in Germany.

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At a glance

What is limited?

Mouth opening and potentially eating, drinking or oral care.

What is examined?

The course, joint, muscles, teeth and signs of inflammation.

When is immediate action needed?

With worsening restriction, swelling or fever; call 112 in Germany for breathing problems or swelling with difficulty swallowing.

Knowledge in motion

Explained in 36 seconds.

Three steps. Straight to the point.
Explanations are also shown on screen.

Short film (German): Why will the mouth not open properly?

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Silent film in German · English explanations in the three views above

Often confused

Cannot open or cannot close?

Restricted opening and being unable to close the mouth are different problems. Both require assessment of their cause.

Quick answers

Is it always a jaw-joint disorder?

No. Infection, injury and other conditions can also restrict mouth opening.

Should I simply start stretching?

Not without assessment of a new or worsening restriction. Suitable exercises depend on the cause and course.

What if my mouth is stuck open?

Inability to close an open mouth is a different problem and also needs prompt professional help. Do not try to reposition the jaw yourself.

At the practice

For your consultation

A question to discuss with Dr. med. dent. Niusha Barahmand Pour:

What explains the restricted opening, and what level of activity is appropriate now?

Acute symptoms require prompt assessment; subsequent discussion depends on the findings.

Describe new or worsening restriction directly by phone instead of waiting for a distant routine appointment.

Call about restricted openingFor acute symptoms, call for prompt assessment

Meet Dr. med. dent. Niusha Barahmand Pour

Learning for dental trainees & teamsUnderstand clinical terms and build your knowledge

Build on the simple explanation with clinical terms, key distinctions and a knowledge question.

Trismus: The medical term for restricted mouth opening.
Muscles of mastication: The muscles that enable jaw movement and chewing.
Progressive: Increasing or worsening over time.

Know the difference

Measuring opening describes function but does not explain why it is restricted.

Knowledge questionWhat matters with suddenly worsening restriction?

This question supports learning. It does not assess personal symptoms.

Force the mouth open
Have the cause assessed promptly
Always assume stress alone

Show answer and explanation

Have the cause assessed promptly

Especially with swelling or fever, infection or another urgent cause must be considered.

Sources for further learning

Sources and context

Editorial research: 23 October 2026. This explanation covers general principles and does not replace a personal examination. Suitable treatment is discussed following individual assessment.