What is Temporomandibular Joints (TMJ) Disc Displacement?

To understand Disc Displacement, we need to talk a little about Jaw joints, also known as temporomandibular joint (TMJ). TMJ is the joint articulating the jawbone (mandibular condyle) to the skull bone (glenoid fossa). A fibrocartilage articular disc is separating the articulating surfaces between these two bones. The disc’s role is not limited to separating these bones; it plays a role in arranging the jaw function, such as mouth opening and other jaw movements.

What are the causes and classifications of TMJ disc displacement?

Many factors keep the disc in its natural location between the articulating surfaces. Some of these factors are the disc shape, the ligaments tightly binding the disc to the mandible condyle. Any abnormality of these structures can cause disc displacement. If you ask, what can cause abnormality to the disc or the ligaments? The answer some patients have inherited abnormalities to the ligaments causing joint hypermobility; others might acquire this abnormality secondary to parafunctional habits such as teeth grinding or clenching or even bad habits causing minor trauma such as nail-biting.

This disc’s displacement can cause clicking, sometimes pain, and discomfort during the jaw function, occasionally causing limited mouth opening. There are two main categories of temporomandibular joint disc displacement.

  1. Disc displacement with reduction (DDWR)
  2. Disc displacement without reduction (DDNR)

Disc displacement with reduction (DDWR) causes the jaw to click

Temporomandibular joint disc displacement with reduction (DDWR) indicates that the disc is displaced in a closed-mouth position but reduced back to a regular place, in an open position. This reduction causes a click sound. If the reduction happens during minimum mouth opening, the symptom is early click. The late click happens if the reduction happens during wide mouth opening. Some patients might have softer clicking when closing. It is also worthy of mentioning that when DDWR advanced, it can cause episodic jaw locking.

Disc displacement without reduction (DDWR) is one of the causes of sudden limited mouth opening

The TMJ noised can be identified by your dentist using the same instrument that is used to hear your heart!

Temporomandibular joint displacement without reduction (DDNR) indicates that the disc is displaced in the closed-mouth position but can not reduce to its normal location in an open position. Usually, the patient has a history of clicking, and suddenly, the click will disappear, and the patient will complain of limited mouth opening. If managed DDNR with limited mouth opening can improve to be DDNR without limited mouth opening.

Diagnosis and Course of Treatment

For clicking, DDWR: most patients know that they have disc displacement; however, they usually seek orofacial pain specialist help when the click is painful or associated with episodic locking. It is always recommended to seek an orofacial pain specialist consultation when a patient has clicking even without pain to help the patient identify the cause of the click and teach the patient the way to avoid the click if possible and prevent the progression into DDNR associated with limited mouth opening.

For limited mouth opening, DDNR: MRI might be needed in a few cases. Most of the time, the orofacial pain specialist will diagnose the condition by clinical examination.

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