“I have TMJ.” People are told this all the time by dentists and doctors to basically say they have something wrong with their jaw joint. This is an unfortunate term as there is no useful information in this term.
TMJ is an acronym for temporomandibular joint where the temporal bone of the skull interacts with the ball (condyle) of the mandible. It is our jaw joint which sits just in front of the tragus of the ear. This is basically a loose ball and socket joint that can do complicated movements in all three axes of direction. This joint can move like a hinge. It can slide forwards and back. It does a combination of these when you open. It can also rotate to the side which is what it does when you move your jaw sideways. This ball is not locked into a socket like the hip joint is. It is held against a shallow depression in the bottom of the skull by a complex array of ligaments and muscles. To add to the complexity it has a small cartilage pad that sits on top of it that is called the disc. This disc sitting on top of the ball is loosely attached to the condyle and the bottom of the skull and the muscles in the area. The disc/pad normally travels back and forth with the ball of the condyle and acts like a lubricating cushion.
These simplified diagrams are trying to show a cross section of the TMJ and how the disc is contained by the muscles and ligaments around it (kinda like our knee caps) and that the disc moves forwards on top of the condyle when the mouth opens.
Note: the diagrams below face the opposite direction to the above diagram.
Healthy TMJ - Mouth closed
Healthy TMJ - Mouth open
The mouth and teeth do a huge amount of work for us and are subjected to all kinds of pressures and angles of force. The muscles and ligaments of the jaw joint area can be damaged from overwork or trauma. They can be stretched and torn. There may be a notable event when this happens or it may just deteriorate over time. When this happens this disc may no longer be anchored properly on top of the condyle. Instead it will usually sit in front of the condyle and the person will hear and feel a loud click or pop when opening as the ball forces its way under the disc. Sometimes these are loud enough for other people to hear. This is called an Anteriorly Displaced Disc.
What happens is: when we start opening, the condyle hinges and slides forwards and pushes up against the disc sitting in front of it. It squishes up against it until the disc suddenly pops back on top of the disc and then travels with it to full opening. As the person closes again they will often hear a much softer click as the disc slides back off the disc at some point near the end of closing. So with an anteriorly displaced disc there is often a double click heard during jaw opening. If you watch the opening and closing from the front you will see the jaw will first open towards the side that has the displaced disc. This is because the out of place disc is allowing the jaw to hinge open but will not allow it to slide which causes this asymmetric opening at first. When the disc pops back on top the jaw will swing to the middle again and the jaw will open normally
Sometimes the forward sitting disc is too squished up and will not allow the condyle to pop on top. This is called a Closed Lock. Normally we can open about 40-45 mm from the biting edges of the top and bottom teeth (three finger widths held vertically). With a closed lock we are down to two fingers or 25-30mm.
PAIN is variable. For some people the pain is very bad when there is an acute situation with lots of inflammation and muscle spasming causing pain to radiate all around the area. For others it is simply an annoyance that may be embarrassing if it is overly loud.
An Open Lock can happen if the person opens too wide and the condyle gets stuck in front of the bulge of bone in front of its socket. This is easily fixable by someone standing behind the person, reaching into the mouth with both hands and placing thumbs behind the teeth of the lower jaw and pushing downwards and then drawing the mandible back. The thumbs go onto the pads behind the back teeth. Sometimes the lower jaw can snap back into position so it is a good idea not to have thumbs in position to be bitten.
The Bad News
There is no predictable treatment readily available. Recapturing an anteriorly displaced disc and having it heal back into position is a very tricky treatment that takes well over a year and requires 100% patient compliance and then still has a success rate of less than 50%. It involves opening the mouth and getting the disc back onto the condyle and then closing to the point just before the disc falls back off the condyle. The jaw is kept open at this point with the condyle sitting in the correct position. Then a chairside splint is made to keep it there and the jaw is not allowed to close all the way or the disc will stay forward again. The dental lab then fabricates a positioning splint to keep the mouth open. The person is not allowed to close past this point. They have to somehow eat and sleep with this splint. When they take it out to brush their teeth they are not allowed to close past this critical point or all progress will be lost.
After 9 to 12 months the dentist grinds a little bit off the splint to allow the person to close a little farther. Over the next several months the splint is gradually ground down to nothing as the disc is supposed to be recaptured and the tissues around it reconstituted.
I have also witnessed a “disc recapture” for a closed lock situation where the dentist numbs the damaged joint, puts the person in a headlock, and manipulates the lower jaw downwards, then forwards and the upwards to bring the disc back into position and then a splint is also made and the same process above is done. This is a very tricky thing to perform.
Surgery and TMJ joint replacement were tried in the 1990’s but the results were poor if not worse.