Pain in the TMJ
Pain in the TMJ from Occlusal Trauma...
As for actual, true TMJ pain, once we rule out the "intracapsular" problems we discussed earlier, we can then focus on a small muscle which I pointed out earlier in diagram of the TMJ capsule - you know that little one that implants itself into the capsule of the joint itself. This important muscle is the one that separates the teeth by opening the jaw slightly. It opposes the powerful closing muscles discussed earlier and is called the Lateral Pterygoid Muscle.
I won't go into the full anatomy of why, but when the Lateral Pterygoid contracts, it forces the mandible to rotate open, parting the teeth slightly (unlike the image at left which is an exageration to make a point!)
In normal function when this "jaw-opening" muscle contracts, the other, opposing muscles of "jaw-closing" are turned off. That is what we call "coordinated muscle movement."
The true definition of clenching occurs when both the opening and closing muscle groups are contracting at the same time, which is called "uncoordinated muscle movement." When
this happens, you are neither opening nor closing, or you are doing both depending on how you look at it.
When it comes to the topic of TMJ pain, here is the important point - this opening muscle is attached not only to the mandible but also to a pad of cartilage called the "Temperomandibular Joint Disk" that sits between the skull and the mandible.
This disc is what cushions the intense force between these two bones during closing and mandibular movement and prevents the bone on bone contact which is never good for any joint.
During normal mandibular movement, the disk and the lower jaw bone move together up and down a slope on the temporalis bone. So now try to imagine what happens if both sets of muscles are contracting at the same time.
The Effect of Clenching on the TMJ Disk...
During clenching, the teeth are locked together so the mandible cannot move any further. The muscles of closing are still pulling hard against the places where they attach to the bones of your face and head. The muscles of opening are still pulling hard against the capsule of the TMJ in general and the dikc within that joint in particular.
Clenching = both muscle groups working at the same time, pulling on whatever they are attached to. If it continues, something has to give. You will learn later how the teeth will get punished and cause a bunch of symptoms, but when it comes to the TMJ it is the disk that eventually gets pulled right out of the socket which causes all of the symptoms and signs of dysfunction within the joint.
In other words, the ligament that holds the disk in place gets stretched and the disk begins to get loose in the capsule of the joint. The popping and clicking sound is actually the disk getting stuck either behind or in front of the lower jaw bone. This loosening of the TMJ disk can even cause locking of the jaw in an open or closed position if the disc gets really out of position.
If you look at the diagram to the right you will see different positions of the TMJ as if the head was pointed to the left. In normal function the disk is moving forward and back along with the lower jaw. But when the disc is loose it may get stuck in front of the lower jaw bone causing clicking, popping, or locking.
Along with an explanation of how it happens is the answer to the question why it happens - the muscles being in perpetual, uncoordinated spasm in response to the teeth not being balanced with the TMJ.
The good news is that once you balance the teeth to the centric relation position of the lower jaw, the disk will begin to tighten back up in the joint and the pain and noises will go away.
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