The temporomandibular joint is an important joint of the skull, which is essential for all daily functional activities of the mouth, such as speaking, eating, and singing. It is a very special joint, one of the few joints in the human body with an articular disc (other familiar joints are the knee joint, whose articular disc is the meniscus), and the only joint in the human body that requires bilateral joint linkage (this is a very important point, and many problems arise here). Every time it opens and closes its mouth, every time it chews, it brings pressure of different sizes, every time it laughs, it has to run back and forth to match the degree of mouth opening, it and the teeth and tongue are good friends, they rest together and work together, but of course if one of them is sick and uncomfortable, the other two are likely to be affected. Let’s see how the temporomandibular joint looks like. The temporal bone of the skull and the condyle of the mandible form this joint, and there are joint discs between them to play a cushioning role, because we are walking upright, unlike other animals, so many joints in the human body have evolved accordingly to adapt to this change. The TMJ relies on the joint discs to produce a forward sliding motion when opening the mouth, increasing the degree of mouth opening. The movements of our jaws on a daily basis can include those shown above, including opening the mouth, closing the mouth, extending the jaw forward, retracting the jaw, and tilting the jaw to one side. All joint movements on the human body are driven by muscle contraction. The movement of the jaw is the involvement of our masticatory muscle system, including: the occlusal, temporal, bicipital, internal pterygoid, and external pterygoid muscles, while there are many ligaments and joint capsules around the joint to limit excessive and incorrect movements of the joint. Therefore, when problems or diseases occur in the power muscles and the limiting ligaments and capsules, the joint will move incorrectly, which is one of the pathogenesis of temporomandibular joint disorder of concern. The diagram above shows us that when opening and closing the mouth, the condyle of the mandible slides forward and backward in a wide range, which is an important and necessary movement of the joint, as I said earlier. Does it seem to move differently on both sides? Does the bone seem to bounce and make a loud sound when you open it? As if the opening will have a stuck feeling? Does it seem like it’s not only stuck but also hurts when it’s opened wide? Does it seem like the two sides move separately when opening? Does it seem like there is a rubbing sound and some pain here when opening wide? These are also the most common signs of TMJ disorder. Next, let’s go inside the joint and see what is happening inside the joint. Inside the joint, we can see that the articular disc divides the TMJ into the upper temporal bone and the upper articular surface of the disc to form the superior articular cavity, and the condyle of the mandible and the lower articular surface of the disc to form the inferior articular cavity. When we open the mouth about one finger size (1cm), it is mainly the condyle and the lower articular surface of the articular disc that do the rotation and slight rolling. When continuing to open wide, the articular disc and condyle come forward together and the superior articular surface of the articular disc slides a great deal against the temporal bone. Next, we will look at the complete process from closed mouth to open and closed again. 1 is when the mouth is closed, 4-5 is when the mouth is completely wide open, and you can see that the articular disc and condyle slide forward a lot. 8-1 is when the mouth is closed again, and the condyle and articular disc go backward to their resting position. It is the pterygoid muscle, which is a very important muscle in the front, that drives the condyles and discs to slide forward, and it is the joint capsule around the joint that restricts and maintains the discs in the correct position inside the joint.