Jaw clamp

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Classification according to ICD-10
R25.2 Cramps and spasms of the muscles
ICD-10 online (WHO version 2019)

A jaw clamp is the limited or complete impairment of the mouth opening. If the mouth opening is obstructed due to a tonic spasm of the masticatory muscles , the jaw clamp is medically referred to as trismus (from Greek trizein , 'crunch'). As a result, the mouth cannot be opened at all or only with severe pain. If, on the other hand, the closing of the mouth is impeded, one speaks of a mouth or jaw lock.

Classification of the jaw clamp

The cutting edge distance (SKD) can be measured and documented to objectify the findings and to monitor the progress. This is the distance between the cutting edges of the upper and lower front teeth . In healthy people, the cutting edge distance is about three cross fingers , i.e. the added widths of the patient's index finger , middle finger and ring finger .

  • Grade I: slightly restricted mouth opening
  • Grade II: maximum mouth opening 10 mm
  • Grade III: maximum mouth opening 1 mm.

Unless it is a mechanical disorder of opening the mouth, the opening of the mouth will vary depending on the exertion and anxiety of the patient and can vary by several millimeters. In the course of longer treatment, patients often relax a little and the mouth opening improves. A slight improvement in the mouth opening is often crucial to enable the dentist to treat the underlying inflammation (e.g. incision of an abscess , treatment of a dentitio difficilis or an inflamed extraction wound, alveolitis sicca ).

Muscle cramp

Since the mouth closers ( musculus masseter , musculus temporalis , musculus pterygoideus medialis ) are much stronger than the mouth openers ( musculus digastricus , musculus mylohyoid , musculus geniohyoid , musculus pterygoideus lateralis ), a generalized spasm of the jaw muscles leads to a spasmodic closing of the mouth. until full contact of the rows of teeth.

A tonic masticatory muscle spasm with jaw clamps (formerly also called jaw cramp ) can occur, for. B. can be observed at:

Numerous drugs, including amphetamine and amphetamine derivatives such as MDA , MDE and MDMA (see also speed , ecstasy ), can trigger trismus as an undesirable drug side effect .

Local inflammation

Local inflammation in the masticatory muscles can cause a clamp. They occur mainly as a side effect of the eruption of the wisdom teeth ( Dentitio difficilis - difficult wisdom tooth eruption) or after surgical removal of the wisdom teeth .

This causes the tissue around the teeth to become inflamed and swell up. The pain accompanying the inflammation leads to relief. Especially when trying to open the mouth, the masticatory muscles almost involuntarily cramp as a protective reflex and thus prevent a complete mouth opening.

Mechanical reasons

A disc prolapse in the temporomandibular joint is a possible cause. As a result, the mouth opening is mechanically hindered. If the disc prolapse is one-sided, the lower jaw deviates towards the diseased side when the mouth opens.

Furthermore, a lower jaw fracture at the level of the joint neck ( collum fracture ) should be considered.

More rarely occurs trismus at a inflammation of the temporomandibular joint , or its immediate vicinity, so at an inflammation of the tongue , the parotid gland , the periosteum or any abscess in the tissue around the tonsils ( peritonsillar abscess ). A clamp can also develop if the lower jaw fractures in the molar area.

After conduction anesthesia of the lower jaw of the inferior alveolar nerve, a jaw clamp is possible. This occurs as a result of irritation of the puncture channel, infiltration of the anesthetic into the masticatory muscles or, much less often, because of a developing syringe abscess.

Differential diagnosis

A distinction must be made between the jaw clamp (difficult opening of the mouth) and the jaw lock (impossibility to close the mouth - e.g. in the event of a dislocation of the temporomandibular joint or a zygomatic arch fracture - both represent a mechanical lock for the mouth closure).

It is typical for a jaw clamp that it can be temporarily remedied with local anesthesia (conduction anesthesia of the lower jaw). Since this eliminates the sensation of pain, the patient no longer builds up a protective reflex against the otherwise painful stretching of the masticatory muscles. In this way, this area is accessible for treatment even with a jaw clamp if it is possible to apply local anesthesia lege artis . If necessary, local anesthesia is performed extraorally. The puncture is made below or behind the angle of the jaw or between the muscular process and the articular process - just above the mandibular incisura .

Therapy of the jaw clamp

The jaw clamps, which are mostly caused by inflammation and which the dentist sees, almost always disappear with the treatment and the subsiding of the causal inflammation.

In very rare cases, however, a - usually slight - jaw clamp remains even after the inflammation has subsided. This is then treated with stretching exercises, which are carried out at the same time as possible with warming (e.g. red light ). The patient pushes a stack of wooden spatulas between the upper and lower posterior teeth. When the maximum possible number of wooden spatulas has been reached, he pushes another wooden spatula into the middle of the stack - between the other spatulas - so that the mouth opening is expanded by a further 2 mm. This exercise is then increased daily.

If the disk is displaced (anterior disk displacement without reduction), therapy is carried out by reducing the disk, either manually or, if this is difficult, using a reduction splint.


In colloquial terms, the lock of the mouth is also the temporary inability to speak, similar to the idioms I have no words or I am speechless .

Individual evidence

  1. Trismus: Alphabetical Directory for the ICD-10-WHO Version 2019, Volume 3. German Institute for Medical Documentation and Information (DIMDI), Cologne, 2019, p. 887
  2. ^ Rudolf W. Ott, W. Krug, HP Voller: Clinic and Practice Guide Dentistry. 1st edition. Thieme Verlag, 2002, ISBN 3-13-131781-7 .
  3. A. Müller, RW Schlecht, Alexander Früh, H. Still: The way to health: a faithful and indispensable guide for the healthy and the sick. 2 volumes, (1st edition 1901, 3rd edition 1906, 9th edition 1921) 31st to 44th edition. CA Weller, Berlin 1929 to 1931, Volume 1 (1931), pp. 20 f. ( The jaw cramp of the newborn ), and Volume 2 (1929), p. 21 ( The jaw cramp (masticatory muscle cramp), rigid cramp ).