Dislocated Jaw: Causes, Mechanisms, and Symptoms

How Does a Dislocated Jaw Happen?

A dislocated jaw occurs when the condylar head of the mandible separates from its normal position within the temporomandibular joint (TMJ), often due to excessive mouth opening, direct trauma, or underlying anatomical predispositions.

Understanding the Temporomandibular Joint (TMJ)

To comprehend how a jaw dislocates, it's essential to understand the intricate anatomy of the temporomandibular joint (TMJ). This complex joint connects the mandible (lower jawbone) to the temporal bone of the skull, located just in front of the ear. The TMJ is unique in that it allows for both hinge-like movements (opening and closing) and gliding motions (protraction, retraction, and side-to-side movements).

Key anatomical components include:

• Mandibular Condyle: The rounded end of the lower jawbone that fits into the temporal bone.
• Glenoid Fossa (or Mandibular Fossa): A depression in the temporal bone where the condyle rests.
• Articular Tubercle (or Articular Eminence): A bony prominence on the temporal bone, anterior to the glenoid fossa.
• Articular Disc: A small, oval-shaped piece of cartilage that acts as a shock absorber and facilitates smooth movement between the condyle and the fossa.
• Ligaments and Muscles: A network of ligaments stabilizes the joint, while various muscles (e.g., masseter, temporalis, pterygoids) control its movements.

For normal function, the mandibular condyle moves smoothly within the glenoid fossa and under the articular eminence during opening and closing.

Mechanisms of Jaw Dislocation

A jaw dislocation, also known as luxation, typically occurs when the mandibular condyle moves too far forward (anteriorly) and superiorly, past the articular eminence, becoming trapped in front of it. This prevents the jaw from closing properly.

The primary mechanisms include:

• Excessive Mouth Opening: This is the most common cause. When the mouth opens very wide, the condyle normally glides forward and downward, resting on the articular eminence. If the opening exceeds the normal range of motion, the condyle can slip over the eminence, becoming locked in front of it.

  • Yawning: A common trigger due to the involuntary wide opening.
  • Shouting or Screaming: Forceful vocalization can extend the jaw beyond its normal limits.
  • Large Bites of Food: Attempting to consume overly large items can stretch the joint.
  • Dental Procedures: Prolonged periods with the mouth held wide open during dental work, or during intubation for medical procedures, can lead to muscle fatigue and subsequent dislocation.
  • Forceful Vomiting: The intense muscular contractions and wide opening during emesis can cause displacement.

• Direct Trauma: A direct blow to the jaw, chin, or side of the face can forcibly displace the condyle from its socket.

  • Sports Injuries: Impacts from contact sports.
  • Falls: Landing on the chin or face.
  • Assaults or Accidents: Direct force applied to the jaw.

• Underlying Medical Conditions and Anatomical Predispositions: Certain conditions can increase an individual's susceptibility to jaw dislocation:

  • Ligamentous Laxity: Individuals with naturally loose ligaments (hypermobility syndrome, Ehlers-Danlos syndrome) may have joints that are more prone to dislocation.
  • Shallow Glenoid Fossa: An anatomical variation where the socket is not deep enough to securely hold the condyle.
  • Flat or Small Articular Eminence: If the bony prominence is not pronounced, the condyle can more easily slip over it.
  • Recurrent Dislocation History: Once a jaw has dislocated, the supporting ligaments and joint capsule may stretch, making future dislocations more likely with less force.
  • Neurological Conditions: Conditions like epilepsy or tetanus, which can cause severe muscle spasms, may lead to jaw dislocation.

Anatomy and Biomechanics of Dislocation

When the jaw dislocates anteriorly, the mandibular condyle moves beyond the crest of the articular eminence. The powerful masticatory muscles (like the masseter and temporalis) then go into spasm, pulling the condyle upwards and backwards, effectively locking it in front of the eminence. The articular disc, which normally cushions the joint, may also be displaced or damaged, contributing to the locking mechanism and pain. The ligaments, particularly the temporomandibular ligament, are stretched or potentially torn, leading to instability. This mechanical locking is what prevents the individual from being able to close their mouth.

Recognizing a Dislocated Jaw

The signs of a dislocated jaw are usually quite apparent:

• Inability to Close the Mouth: The most common and defining symptom.
• Severe Pain: Concentrated around the ear and jaw joint.
• Misaligned Bite: The upper and lower teeth no longer meet correctly.
• Protruding Jaw: The jaw may appear to stick forward.
• Difficulty Speaking or Swallowing: Due to the inability to move the jaw normally.
• Palpable Depression: A depression might be felt in front of the ear where the condyle normally rests.

A dislocated jaw requires immediate medical attention for proper reduction (repositioning) to restore normal function and alleviate pain.