Dentists often hear people tell them that they “have TMJ.” The truth is, everyone has two! TMJ is the name of your jaw joints, not a condition. It stands for temporomandibular joint. When a TMJ is painful or not functioning properly, the condition is known as TMD, or temporomandibular joint dysfunction (or disorder). In this post I will introduce concepts of TMJ anatomy, function, disorders, and diagnostic tools.
The TMJs are positioned right in front of you ear canals. You can find them by placing your fingertips in front of your ears and opening wide. You’ll 
feel the top part of your lower jaw stick out when you do this. The top of your lower jaw is part of what forms the TMJ. The following picture shows the major parts of the joint. The upper bone portion is part of the temporal bone, and the lower portion, the condyle, is part of the lower jaw. Between the two bones is a disc which functions as a cushion that slides between the bones as you lower and raise your jaw. The condyle and disc are controlled by muscles from the front. The disc is also controlled by a ligament in the back. There is a capsule surrounding the entire joint which holds the lubricating joint fluid. In addition, there are nerves and blood vessels serving the joint.
A properly functioning joint moves smoothly, without pain, popping, or a feeling of grinding. TMJ popping is generally what you feel and often hear when the disc slips out of and back into position. This can mean that the disc has become deformed, or the ligament has become damaged to the point that it no longer keeps the disc in place. Pain in the joint can come from one or more of several structures within the joint. Pain can also come from a nearby structure and feel as though it’s coming from the joint. This is known as referred pain. The image to the left shows areas that a neck muscle can refer pain to. The source of the pain are the black dots, the areas where pain is felt are in red.
Determining the source of pain or the reason for improper joint junction is the key to finding the appropriate treatment. The main tools in diagnosing a condition include:
- Patient’s health history
- History of the current condition
- Examination
- Evaluation of joint sounds
- Imaging, including x-rays and MRI
A three dimensional x-ray scan provides valuable information about the bones of the TMJ, including changes in bone shape, bone surface
degeneration, growths, and position of the condyle. The image below shows a scan of normal TMJs:
An MRI, or magnetic resonance imaging allows us to see soft tissues, such as the disc and muscles, and their position relative to bony structures. The image below is an MRI of a normal TMJ:
Other diagnostic instruments include stethoscope, doppler, and joint vibration analysis devices. In future posts we’ll look at diagnosis of TMJ disorders and potential treatment options.