TMJ Disorders

- feature of unhealthy teeth

Illustration of TMJ Disorders caused by occlusal problems and the stages of deterioration


TMJ disorders refer to things going wrong in the temporomandibular joint (usually abbreviated to "TMJ"). The disorder is abbreviated as "TMD" but many people will say "I've got TMJ" meaning they have TMD or a problem with their TMJ.

The TMJ is a unique joint in our body that can move in multiple directions – much like a control stick in a fighter jet – with some of those movements involving the jaw coming out of its socket in the skull. It is designed to work that way – part of its normal function is to come out of joint. Another unique feature is the disk or cartilage that comes between the jaw and the socket as it is composed of a different material than all other body cartilage (called fibro-cartilage).

TMD can cover many different problems such as capsulitis (inflammation of the envelope surrounding the joint), inflammation of the ligament, disk displacements, chronic degenerative bony deformations (changes in shape of the jaw bone) and arthritis.

An accurate diagnosis is required to determine whether the joint is the cause of pain in that area or if it's the muscles associated with movement of the jaw.

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Reasons this is not good:

TMD, or "TMJ", can:

  • be painful,
  • restrict jaw movement
  • change how the teeth meet (your occlusion) and hence produce (greater) problems with the teeth
  • in later stages lead to arthritis in the bones of the jaw joint
  • be difficult to correct

Possible causes:

  • Trauma – for example a blow to the jaw
  • Genetics – the teeth may grow in ways that create a poor relationship between the occlusion and the jaw joint.
  • Orthodontics – the newly positioned teeth may interfere with a stable bite and the peaceful functioning of the muscles
  • Reconstructive dentistry – similarly, newly placed crowns, implants, or veneers can be the causes of interferences that stimulate the muscles and lead to deterioration of the TMJ

See also:

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Video Transcript

Using BiteFX to explain the occlusal causes of TMJ Disorders

A TMJ disorder is basically something going wrong with your jaw joint.

This video addresses one cause of TMJ disorders, namely that your occlusion isn't right – that is that your teeth do not come together correctly as shown here.

Before explaining why malocclusion can affect your jaw joint, we should first introduce you to your temporomandibular joint, or TMJ.

First, here's how your jaw works.

  • You have a muscle under your jaw that pulls it down to open
  • Then to open really wide, your jaw actually comes out of its socket and is pulled forward by another muscle.
  • To close these muscles relax and your strong closing muscles go into tension and bring your teeth together.

Now let's take a closer look at the joint.

  • The upper part of your jaw, called the condyle, fits into a socket in your skull, called the fossa.
  • Between the condyle and the fossa is a disk called the TMJ disk – shown here in orange – which is as tough as cow hide.
  • The disk tracks with the condyle as it moves forwards and backwards.
  • At the back of the disk is soft spongy tissue, shown in yellow, which expands and contracts to fill the void as the condyle moves in and out of the fossa.
  • A lateral muscle tenses to pull the jaw forwards
  • And its partner tenses as the jaw closes to help hold the TMJ disk in place.
  • The vertical lines in these animations are placed to show where the jaw should be when it is properly seated.

So you can see that there are several elements that make up the jaw joint and they need to work in harmony for the healthy functioning of the jaw.

When your jaw is closed the lateral muscles should be at rest, as shown on the left. However, occlusal problems can cause these muscles to be in tension and hyperactive, as shown on the right. They pull on the TMJ disk and jaw for much longer times than they should.

So let's see how long periods of this hyperactivity can affect the jaw joint over time.

We start with the normal open and close motion.

Now we show what can happen over a long period of time if the disk is always being pulled by that upper lateral muscle – a process that could happen over years.

You can see that a few things are happening

  • The ligaments holding the disk to the back of the condyle stretch
  • The thicker part at the back of the disk pushes the jaw back a bit
  • So the jaw is no longer sitting snuggly in the disk
  • The jaw is also being pushed back into the soft tissue which is quite sensitive so it causes pain

Now let's see what happens when the jaw opens and closes

  • As the jaw opens and is pulled forwards, the condyle jumps back into place – usually indicated by a clicking sound.
  • It then tracks with the disk and on closing clicks off again to return to its starting position

If your jaw is clicking, this is what is happening – even if you are not feeling the pain that the animation suggests might be happening.

Now we show further stretching of the ligaments and the jaw pressing back harder into the tissue, causing more pain.

In this stage of deterioration the condyle doesn't jump back on to the disk so the clicking stops and, instead of riding on the tough disk, the condyle is rubbing on the stretched ligaments at the back of the disk which, over time, eventually perforate so the condyle rides up and now rubs bone-on-bone.

The disk is just crumpled in front of the jaw and may make it difficult for the jaw to open.

Pain may actually reduce at this point because the sensitive tissue is no longer bearing quite as much force.

If the lateral muscles have been pulling on the condyle excessively over time, they can actually cause the condyle to change its shape – called beaking of the condyle. Something that doctors and dentists can observe in x-rays of the jaw joint. Also the condyle and fossa are wearing each other down because there is just bone rubbing on bone – something that is likely to cause arthritis in the joint.

If this type of occlusal problem is identified early by your dentist, it can be corrected before any of this deterioration happens.

An appropriately trained and experienced dentist may be able to help you recover from early stages of TMJ disorders, but the further along you are on these stages of deterioration the more likely it is you'll need the attention of a TMJ specialist.