What is an Internal Derangement?
Internal derangements involve anterior displacement of the disc that acts as a cushion between the skull and lower jaw. In the early stages, the anteriorly displaced disc returns to its normal position during mouth opening and is accompanied by a clicking or popping sound. This is referred to as “anterior displacement with reduction.” In later stages, when the disc becomes more anteriorly displaced, it acts as a barrier to condylar movement and limits mouth opening. This is referred to as “anterior displacement without reduction.” It has also been referred to as “closed lock.”
What Causes Displaced Discs?
There are two main causes of disc displacement. The most common cause is trauma to the lower jaw. Depending on the amount of trauma, there can be anterior disc displacement with or without reduction. The other cause is a change in the frictional properties of the joint due to degenerative changes in the joint surfaces caused by chronic tooth clenching and grinding habits (bruxism) or arthritis.
Who Can Get Displaced Discs?
Studies using MRI and arthroscopy have shown displaced discs in people who have symptoms of TMJ pain and dysfunction as well as those who have no symptoms. In other words, many people without TMJ problems have displaced discs.
Is a Displaced Disc Painful?
Pain can result from an anteriorly displaced disc. However, it does not arise from the disc itself. Rather, it is caused by compression of the highly innervated tissue attached to the posterior aspect of the disc (retrodiscal tissue) that becomes located in the gliding area between the condyle and the skull when the disc becomes displaced anteriorly.
Should a Displaced Disc be Treated?
A displaced disc does not necessarily need to be treated. If the disc restricts movement and causes pain, treatment may be required. However, if a displaced disc is present with no pain or limited mouth opening, no treatment is needed.
We are grateful to Dr. Daniel Laskin, Adjunct Clinical Professor and Chairman Emeritus at Virginia Commonwealth University School of Dentistry, Oral and Maxillofacial Surgery, for his many years as our clinical advisor and for writing the content in this section.