The TMJ Disk — The Forgotten TissueBy Jim McKee on December 7, 2020 | comments
“It's just a clicking joint, it's no big deal.”
“I've clicked for years and it hasn’t been a problem for me.”
“I used to click but it stopped, so I guess it isn't a problem.”
These statements are common when patients and dentists discuss clicking jaw joints. Clicking joints have become so common they are accepted as normal or a variation of normal. While some patients have clicking joints that are stable and do not cause any problems, many other patients have significant issues.
According to Alomar, the articular disk is the most important anatomic structure of the TMJ (Fig. 1). It is a biconcave fibrocartilaginous structure located between the mandibular condyle and the temporal bone component of the joint. It functions to accommodate a hinging action, as well as the gliding actions between the temporal and mandibular articular bone.
The articular disk is a roughly oval, firm, fibrous plate with its long axis being transversely directed. It is shaped like a peaked cap that divides the joint into a larger upper compartment and a smaller lower compartment. Hinging movements take place in the lower compartment and gliding movements take place in the upper compartment.
The superior surface of the disk is said to be saddle-shaped to fit into the cranial contour, while the inferior surface is concave to fit against the mandibular condyle. The disk is thick, round to oval all around its rim, divided into an anterior band of 2 mm in thickness, a posterior band 3 mm thick, and thin in the center intermediate band of 1 mm thickness.
More posteriorly there is a bilaminar, or retrodiskal, region. The disk is attached all around the joint capsule except for the strong straps that fix the disk directly to the medial and lateral condylar poles, which ensure the disk and condyle move together in protraction and retraction.
The disk plays a crucial role in many of the key factors seen in dentistry. Here are some of the key issues the disk influences:
- The disk condition and position influence maxillary and mandibular growth and development. If the joint is injured and the disk is herniated during the growing years, the likelihood increases for incomplete or arrested growth of the mandible and the maxilla.
- The disk condition and position influence the condition of the condyle. The disk protects the condyle during compressive loading and in movements of the mandible. Disk displacements almost always precede osseous changes in the condyle.
- The disk influences the occlusion and can cause changes in the occlusion. A herniated disk can either increase or decrease the vertical dimension of the TMJ. If the disk herniates and the condyle functions against the thicker posterior band of the disk, the vertical dimension most likely increases and there is a resultant Class III bite shift. If the disk herniates and the condyle functions against the retrodiskal tissue, the vertical dimension most likely decreases and there is a resultant Class II bite shift.
- The disk position influences pain since the disk can herniate and compress or impinge on various structures in the jaw joints. In addition to the soft tissue compression of the disk, the exposed condyle that is loaded without soft tissue protection can also hurt.
- The disk influences airway since altered growth of the mandible and maxilla will negatively influence mandibular and maxillary projection. In many of these cases, the result is compressed oropharyngeal airway space.
- The disk influences facial esthetics since facial asymmetries and retrognathic mandibles and maxillae are often the results of the growth changes that occur in structurally altered TMJs.
MRI imaging offers the opportunity to assess the disk condition and the disk position. Dentistry has typically restricted joint imaging to the hard tissue with imaging such as transcranial radiographs, tomograms and CBCT.
While imaging the hard tissue is important for treatment planning, imaging soft tissue is equally important yet rarely obtained. Understanding the role the disk plays in growth and development, the condition of the condyle, the occlusion, the airway, pain and facial esthetics, the easier it will be to order MRIs to assess the condition and the position of the TMJ disk.
Jim McKee, D.D.S., is a member of Spear Resident Faculty.
Alomar X, Medrano J, Cabratosa J, Clavero JA, Lorente M, Serra I, Salvador A, et al. Anatomy of the temporomandibular joint. InSeminars in Ultrasound, CT and MRI. 2007;28(3):70-183. WB Saunders.
Piper, DMD MD, Mark. "Temporomandibular Joint Imaging." Handbook of Research on Clinical Applications of Computerized Occlusal Analysis in Dental Medicine. IGI Global, 2020. 582-697. Web. 24 Oct. 2019. doi:10.4018/978-1-5225-9254-9.ch009