A TMD or Temporomandibular Disorder or Dysfunction occurs when there is a “Disorder” or “Dysfunction” of the arrangement of the structures within the TMJ (Temporomandibular Joint).  When things are out of order, then they can’t function properly – hence the Dysfunction.  This is one of the major problems treated at Mountains TMJ & Dental Sleep Medicine in Katoomba.

This is different from Orofacial pain (which we also treat), where there is pain in the head and neck region from various possible causes.  In my clinical experience, the vast majority of patients who see me about facial pain have a TMJ Dysfunction involving a mismatch of the structures within the joints whenever their teeth are together.  This is also commonly known as an “Internal Derangement” of the TMJ.

Symptoms of TMDs are described in a previous post – What is TMD?

But why are the structures deranged in the first place?

Looking it up online, you will see such suggestions as –

  • autoimmune diseases (in which the body’s immune cells attack healthy tissue)
  • infections
  • injuries to the jaw area
  • dental procedures (even prolonged mouth opening during dental treatment)
  • overextending the jaw when insertion a breathing tube before surgery
  • medication side-effects
  • stress
  • muscle fatigue
  • hypermobility
  • and others…

But if you look closely at that list, it is hard to see how most of them could cause the joint structures to be out of order – with the possible exception of injuries to the jaw area.  But boxers take very heavy blows to the jaws as a matter of daily recreation, and don’t have TMDs, so this would need to be a massive injury, typically limited to a serious motor vehicle accident with major head trauma and broken bones, or military injuries.

I agree that any of these things can be the final straw in initiating symptoms of pain related to a joint dysfunction, but they are not likely to cause the joint dysfunction.

The Growing Jaws.

My friend and mentor, Professor John Mew, teaches that it is all about tongue posture.  He often describes this as being causative at any stage of life, but I suspect that it is only having such a significant affect during growth and development of the jaws.

You see, as the jaws are growing, the tongue is supposed to be resting against the roof of the mouth, the palate, and applying gentle constant pressure out to the sides and forward.  As the tongue grows it pushes the palate to grow laterally (to the sides) and anteriorly (forward).  The palate is actually the floor, or lower surface of the Maxilla which is the major bone of the face (or bones as it is in two separate parts, left and right).

The palate is also the floor of the nose, so as the maxilla grows, so does the nasal airway. Changes in the palate are reflected in the floor of the nose.

As the maxilla grows in width and forward, under the influence of the tongue, it makes the space for the tongue to continue fitting against the palate, and it makes the space for the growing mandible (lower jaw) to grow forward.  That forward growth of the mandible is also stimulated by the tongue position (or tongue posture).

The tongue posture is obviously important for proper growth and relationship of the jaws. 

When things go wrong…

So, what happens when things go wrong?  Why would the tongue not be in its proper position?

One thing that prevents the tongue from functioning properly is a tongue tie.  This is a big subject in itself, so you can look it up here – https://kidshealth.org/en/parents/tongue-tie.html

The other major cause of poor tongue posture is mouth breathing.  This is another subject which I will discuss in another post soon.  But for now, the basics are –

  • you should always breathe through your nose – in and out…
  • your lips should always be together while breathing
  • your tongue should be in the roof of the mouth while breathing

If these things apply, you cannot breathe through your mouth. 

To breathe through your mouth, you have to take your tongue away from the palate, as it is blocking the way for the air to pass through.  So mouth breathing prevents you from maintaining proper tongue posture.

While mouth breathing, the mandible drops down and the teeth stay apart.  Also, the maxilla has a natural tendency to grow down and forward, so during mouth breathing, the tongue is not there to control that downward growth.  The end result is a long face with narrow jaws, and not enough space for the tongue to sit where it is supposed to be.

While the jaws are separated, the teeth grow into whatever space is available to them, but they are not biting together for enough time for them to interlock properly.  This is the foundation of a Malocclusion (bad bite) which will need orthodontic treatment at some stage.

While all of this growth – or distorted growth – is happening, the joints are also forming and the joint structures are being arranged.  This picture shows the proper relationships within the joints, including the “Condyle”, “Disc” and “Temporal Fossa” and “Articular Eminence”. 

Healthy TMJ

When growth is healthy, with nasal breathing and good tongue posture, the joint forms with these structures in the correct relationships when the teeth are together. 

So, what happens to the joint?

But if the growth is happening with the mouth open, then these structures develop in the right relationships with the mouth open.  Then the teeth need to come together when you bite – but they are not in their correct positions, so they will distort the position of the mandible (and the condyle) whenever the teeth come together.  The condyle is typically shifted backward in the fossa in this situation.

The muscles attached to the front of the disc tend to pull the disc forward so that the thicker portion of the back of the disc comes forward to fill the space made by the distorted condyle position. 

But a muscle constantly working like this will eventually go into spasm (and there are many things which can instigate this).  When it does, it can pull the disc further forward to a position where it is “Displaced” when the teeth are together – it is sitting in front of the condyle.

Posterior Condyle and Anterior Displaced Disc

When the disc is displaced like this, it will commonly cause a clicking sound as the condyle moves forward and pops onto the disc, and then again during closing as the condyle pops off the disc again. See the image at the top of this post.

This distortion in the position of the condyle while the teeth are together cannot happen after growth is completed without a major traumatic injury.  The clicking can start later in life, and so can the pain in the joints and muscles – but only if, during early growth and development, the condyle position in the fossa is distorted.

But I don’t have a long face!

Something similar can happen where the joint grows with the teeth apart, but the growth does not take off in a vertical direction.

The joint position is still distorted when the teeth are together, but there is no long face.

There are also those (and I saw on in the surgery yesterday) who have only a mild underdevelopment of the jaws and looked OK at the age of thirteen when all of the permanent teeth (other than wisdom teeth0 had come into place. The teenage boy I saw yesterday didn’t seem to have a major problem and he had, if anything, a slightly short face…

But when I asked if he had any problems, he told me that he had developed a click in his left TMJ. Sure enough, on examination, I identified a displaced disc (with reduction) as shown in the videos below.

So what happened in his case?

The mandible continues to grow during the teenage years, and into the early 20s for boys.

For this young man, the mandible had continued to grow, but was restricted in forward growth by the way the front teeth interlocked. So when it grew longer and could not grow forward, the condyle grew backward, and changed position in the fossa. The same principles apply, but with a slightly different presentation.

What does it look like?

This video shows an anatomical dissection of the joint and what happens to cause clicking.  If you feel a little queasy looking at real anatomical dissections, don’t watch this – you will just have to take my word for it….

This is an edited section from a longer video produced in 1985, showing normal function as well as other joint dysfunctions and injuries.  That video is affectionately called the “Yoint Video” – a name you will understand once you hear the researchers discussing what is happening. You can watch that video here –
The Yoint Video

I hope this helps you to understand a bit more about the origin of your TMD.

Images with the kind permission of Dr Samuel J Higdon DDS