Trismus (limited mouth opening) is a condition in which it becomes difficult to eat, speak, yawn, and sometimes there is a sensation of the jaw being “locked.” In many cases, the cause is multifactorial: a combination of overload of the masticatory muscles and dysfunction of the temporomandibular joint (TMJ). In this article, we will explain this condition in more detail and review a real case of successful treatment of a patient at YAREMA DENTAL clinic.
What is trismus and why does it occur?
Trismus is a condition in which the mouth opens noticeably less than usual, often accompanied by pain or a sensation of “blocking,” as if something is interfering. An adult can normally open the mouth approximately 40–50 mm, and a reduced opening range is usually perceived as a problem.
The most common dental cause is temporomandibular disorders involving the joint and the chewing muscles (TMD).
Trismus may be:
- muscular: protective spasm due to overload, stress, teeth clenching, or bruxism;
- articular: inflammation, degenerative changes, or disc displacement;
- mixed: a combination of several factors.
As stated in a scientific article published in PubMed Central in 2025, trismus significantly affects nutrition, speech, oral hygiene, and quality of life.
What symptoms do patients usually notice?
Most often, patients with trismus report:
- limited mouth opening;
- pain in the joint area near the ear or in the chewing muscles;
- discomfort while chewing;
- clicking or crepitus;
- a sensation of locking;
- morning stiffness or “jaw fatigue.”
An important point: occasional jaw clicking may not be a cause for concern. Treatment is usually necessary when there is pain, restricted movement, and difficulty eating that affects quality of life.
How one patient with trismus was successfully treated
A patient came to the clinic complaining of difficulty opening her mouth and pain in the right chewing muscles upon palpation. Her mouth opening was limited to 11 mm. She also reported bruxism, including clenching and grinding of the teeth.
Visualization of the TMJ joint space on CBCT. Measuring the width of the joint space in different areas helps assess the position of the condylar head. This space is normally occupied by the articular disc; reduced distance between the bony structures may indicate disc displacement or compression.
The probable clinical diagnosis was mixed TMJ dysfunction. Both joint-related and muscular factors were involved. Joint dysfunction was combined with muscle overstrain associated with bruxism.
The patient was referred for cone-beam computed tomography (CBCT) and MRI, which revealed changes in both temporomandibular joints.
On the left side, the disc was displaced but returned to position during mouth opening, whereas on the right side, it did not reposition. In other words, the joint was functioning like a jammed mechanism, which limited jaw movement.
It was found that the jaw was positioned slightly posteriorly, causing tension and improper joint function. There were also signs suggesting that the joint might previously have been overloaded or injured, not necessarily severely.
Thus, one joint was functioning irregularly, while the other was effectively blocked. The jaw muscles became tense to compensate for the problem, preventing normal mouth opening. This led to the development of trismus.
Lateral skull radiograph.This image shows the “skeletal framework,” which determines how the lower jaw moves and how the joints are loaded during chewing.
Imagine a door where the left hinge still moves but with resistance, while the right hinge is jammed and does not move properly. As a result, the door opens poorly. The jaw was functioning in a similar way.
What treatment was used and why it was effective
Natural occlusion without a splint: uneven occlusal contacts may overload the muscles and perpetuate TMJ dysfunction.
Most patients with TMD can be treated successfully with conservative methods, without invasive interventions at the initial stage.
The goal is to reduce overload on the muscles and joint, decrease inflammation and pain, and restore physiological movement.
In this case, treatment consisted of two stages:
Stage 1. Deprogramming. This is a short phase aimed at quickly interrupting the pathological “behavior” of the jaw. The goal is to guide the neuromuscular system into a calmer functional pattern, “switch off” habitual involuntary clenching, and reduce hyperactivity of the chewing muscles. This helps the muscles relax and allows the lower jaw to find a more stable position without excessive tension.
Stage 2. Myorelaxation splint. This is a custom intraoral appliance, most often worn at night. Its purpose is to reduce the load on the chewing muscles, protect the teeth from bruxism/clenching, and unload the joint structures so they can function under more stable conditions.
Occlusal splint (myorelaxation splint) in the oral cavity: the teeth are separated, the load is distributed more evenly, which promotes relaxation of the chewing muscles and reduces overload on the TMJ.
The effectiveness of appliances for trismus treatment, such as splints and mouthguards, has been confirmed by numerous studies. It has also been scientifically proven that their effectiveness depends on regular exercises.
In addition to appliance therapy, the patient was advised to follow a gentle regimen:
- soft food;
- avoidance of chewing gum and excessive biting;
- control of daytime clenching (teeth apart, lips closed at rest);
- physiotherapy.
Clinical progress
Following deprogramming and the use of a myorelaxation splint, improvement was observed: the patient found it easier to open her mouth, muscle pain decreased, and everyday discomfort was reduced. At the intermediate stage, the mouth opening increased from 11 mm to 35 mm.
The table below shows the patient’s condition before and after treatment:
| Parameter | Before treatment | After treatment |
| Mouth opening | Limited | Improved |
| Muscle tenderness on palpation | Severe | Reduced |