TM imaging allows us to gain insights into the anatomy of the TM joint. While TM joint imaging used to be rare, it is commonplace today for dentists to image the TM joints. Since it is impractical to obtain TM imaging for every patient, we need guidelines on when to do so. When we decide to obtain TM imaging, the best option is to perform soft tissue imaging with MRI and hard tissue imaging with CBCT.
Recognizing Patients Who Need TM Imaging
When considering whom to image, an easy way to identify patients who could benefit from imaging is by addressing two questions: How do the patient's teeth fit in the skeletal position, and does the patient experience regular pain?
Assessing Skeletal Position to Identify Indicators for TM Imaging
The first question is how do the teeth fit in a skeletal position? If there is a Class II occlusion in a fully seated condylar position, it may be a good idea to obtain TM joint imaging.
As Manfredini (2016) wrote, “It seems reasonable to suggest that skeletal Class II profiles and hyperdivergent growth patterns are likely associated with an increased frequency of TMJ disc displacement and degenerative disorders.”
Patients who present with Class II occlusions, high mandibular plane angles, anterior open bites, canted occlusal planes, deep bites, overjets, facial asymmetries, and retrognathia all have an increased likelihood of having structurally altered TM joints. If we can recognize these patients and obtain MRI/CBCT imaging, we will have increased confidence when treatment planning and increase case acceptance.
Assessing the Frequency of Patient Pain
The second question to answer when trying to decide if patients could benefit from TM joint imaging is whether the patients have pain on a regular basis. While the frequency of pain is usually discussed, it is also helpful to assess the severity of the pain when determining if TM joint imaging may be helpful.
We were taught that the majority of pain results from muscle hyperactivity; today we know that changes in the condition and position of both the disk and the condyle can have a significant impact on pain levels. Generally, if patients report pain levels greater than five on a 1-10 scale, it may be beneficial to obtain MRI and CBCT imaging to better understand the anatomical risk factors.
Understanding TM Joint Classification in Clinical Practice
If we think about the different types of joints we see in clinical practice, most patients will fall into one of three categories. (Figure 1) Structurally intact TM joints have normal joint anatomy. Structurally altered TM joints at the lateral pole have an intact disk at the medial pole and a displaced disk at the lateral pole. Structurally altered TM joints at the lateral pole and medial pole have a displaced disk at both the lateral and medial poles.
Since the medial pole is the load-bearing portion of the TM joint, if the disk is not protecting the medial pole, it becomes more difficult to dissipate the loading forces generated daily. This increases the likelihood the patient will report pain. Additionally, the disk at the medial pole acts as a three-dimensional gasket to maintain the vertical dimension in the TM joint. If the disk is herniated and cannot maintain the TM joint's vertical dimension, it increases the likelihood the patient will have a Class II bite shift.
In summary, an easy way to decide if a patient should obtain TM imaging with MRI and CBCT is to ask yourself two questions:
- Does the patient have pain greater than five on a 1-10 scale?
- Are the teeth uncoupled greater than the thickness of the disk?
If the answer to either or both questions is yes, it may be a good idea to consider the soft and hard tissue in the TM joint to increase your confidence in diagnosing and treating TM joint patients. Once you start imaging TM joints, be prepared for an increased number of new patients. There are patients in your community looking for TM joint diagnosis, and there are dentists in your community looking to refer patients to someone who can recognize, diagnose, and treat these patients.
Jim McKee, D.D.S., is a member of Spear Resident Faculty.
References:
Manfredini, D., Segù, M., Arveda, N., Lombardo, L., Siciliani, G., Rossi, A., et al. (2016). Temporomandibular joint disorders in patients with different facial morphology: A systematic review of the literature. Journal of Oral and Maxillofacial Surgery, 74 (1), 29-46.