Magnetic resonance imaging of the temporomandibular joint can provide a great deal of information for both the dentist and the patient. This article will review four of the key issues that can be learned from TMJ MRIs.
The first issue that can be ascertained through MRI is the position of the disk in the TMJ. The disk is designed to protect the condyle and the articular eminence during normal function (Fig. 1).
The disk is attached to the condyle through ligaments at the lateral pole of the condyle, the medial pole of the condyle, and at the posterior aspect of the condyle. With normal, intact ligament attachments, the disk can provide coverage to the condyle.
When injuries to the TMJ strain or rupture the ligament, the disk can herniate either anteriorly, medially, or laterally. The hope is that the TMJ can adapt to the herniated disk position and the patient will be able to function with minimal problems.
The second issue that can be determined from MRI is the condition of the TMJ disk. Since the disk is designed to be compressed during function, the disk receives it nutrition from synovial fluid compression as opposed to blood flow.
The disk is avascular in the load bearing portions of the disk. If the ligament attachment is compromised due to joint injuries, the disk can lose its ability to receive synovial fluid compression.
When the disk loses synovial fluid compression, the disk can change shape through losing its normal nutrition. In many cases, the disk desiccates (dries out) and loses its normal shape (Fig. 2).
When this happens, the disk cannot offer protection to the condyle or joint socket and changes can occur at the osseous level.
The third issue that can assess from TMJ MRI is the position of the condyle. In many cases, when the disk is anteriorly displaced, the condyle is displaced posteriorly (Fig. 3).
As a result, there may be a Class II bite shift when the disk is anteriorly displaced. Ikeda discussed this in 2013 when he studied disk displacements in adolescents and young adults. He found disk displacements can cause the condyle to change its position in the fossa with alterations in joint space, which depend on the direction and extent of disk displacement. This is clearly seen with MRI and can be integral to treatment planning patients with structurally altered TMJs.
The fourth issue that can be determined from TMJ MRI is the condition of the condyle. Alterations in the marrow space of the condyle can be seen using MRI (Fig. 4).
Edema in the marrow space of the condyle may be transient or may be part of a process that results in osteonecrosis as Larheim discussed in 2012. The most reliable MRI feature of osteonecrosis in the bone marrow was found to be a combination of edema pattern and sclerosis pattern. Additionally, it is possible to see swelling in the soft tissue outside the condyle which is commonly referred to effusion.
Disk position, disk condition, condyle position, and condyle condition are four of the key factors that can be discovered with MRI. These factors offer valuable information when discussing treatment plans, as well as the prognosis for treatment plans with patients and colleagues.
Jim McKee, D.D.S., is a member of Spear Resident Faculty.
Ikeda K, Kawamura A. Disc displacement and changes in condylar position. Dentomaxillofacial Radiology. 2013;42(3):11–7.
Larheim TA, Sano T, Yotsui Y. Clinical Significance of Changes in the Bone Marrow and Intra-Articular Soft Tissues of the Temporomandibular Joint. Seminars in Orthodontics. 2012;18(1):30–43.