Of all the structural factors that influence temporomandibular joint health, none is as singularly important as "vertical dimension." Vertical dimension is a dental term used to describe how far the lower jaw is allowed to close before the upper and lower teeth make contact and prevent further closure of jaws. It could be thought of as the chin-to-nose distance when the teeth make contact.
The lower jaw is sort of held in a sling of tendons and muscles which move and direct the lower jaw into whatever position is required to get the maximum interdigitation (best bite) with the upper teeth. Any position of the upper jaw which forces the lower jaw into an eccentric position in order to get maximum intercuspation of the teeth has the potential of fulfilling the structural requirement of temporomandibular joint dysfunction. That is, any sideshift, any canting up of one side, any slant, or any excessive slope of the upper jaw can force the lower jaw into a strained and unnatural position in order to get the best bite, or what is known in dentistry as maximum interdigitation or maximum intercuspation. However, there is yet another possibility of fulfilling the structural component of TMJ dysfunction which may have absolutely nothing to do with any sideshift, cant, slant, or slope of the upper jaw. It has everything to do with how far the lower jaw is allowed to close before the teeth make contact and prevent any further closure of the lower jaw.
Of course, everyone is aware of the pain caused by a hyper-extended joint, like a wrist that is bent back to far. How about a hyper-flexed joint? Not a whole lot is heard about that, but let me illustrate its significance. Try putting your right elbow out on the top of a table or desk you are sitting in front of, and let your right forearm extend straight up in the air. Now, bend your wrist backward as far as it will comfortably go. With the left hand, reach up and press your right hand backwards a little more. Feel the pain. That is a hyper-extension of the wrist joint of your right hand. Now bend your right hand forward as far as it will go, with your forearm still standing straight up. Then, with the left hand, reach up and force the right hand even further forward and downward. Did you feel intense pain? That pain is a symptom of a hyper-flexed wrist.
What about a hyper-flexed jaw? Isn't that exactly what happens when the lower jaw is overclosed, because of a lack of, or loss of, vertical dimension? Precisely. Lets take a look at some of the possible causes of an over-closure of the jaw (a loss of vertical dimension).
Excessive wear of the teeth is one cause. It is obvious that if the teeth are worn down shorter, the jaw will have to close down further to get the teeth to come together. Excessive wear can be caused by bruxism, grinding, or clenching the teeth together. It can also be caused by the oral use of abrasive foods or oral tobacco products.
Missing permanent teeth (whether congenital or by extraction) is also a cause of loss of vertical dimension. What happens is that when permanent teeth are removed, and not replaced, the adjacent teeth will drift and "lean over" into the space or gap that has been created. A tooth that is leaning over is not as tall as one that is standing up straight. When the teeth are not as tall as they should be, then the lower jaw has to close down further to get the teeth to come together. Thus, overclosure of the jaw occurs.
Underdevelopment of one, or both, of the jaws is probably the single most common cause. Almost a certain sign of underdevelopment can be identified when a person bites down and half or more of the lower front teeth disappear up and behind the upper front teeth. (This is what dentists call a deep bite.) Crowding of the teeth is another almost certain sign of underdevelopment of the jaw. This crowding is what orthodontists are attempting to treat when they recommend "orthodontic extractions," or the removal of permanent teeth so that there will be enough space for them to align the teeth. This all sounds logical, but what my observations have been, is that when orthodontic extractions have been done, the underdevelopment of the dental arches is exaggerated, and later in life, the bite deepens dramatically. I also observe a very disproportional occurrence of temporomandibular joint dysfunction later in life in those folks who have had orthodontic extractions.
How might you tell if your jaw is overclosed? Simply look in a mirror and notice if half or more of your lower teeth disappear up and behind your upper teeth when you bite down. Then notice if your lower lip sort of rolls forward, leaving a deep curve or crease between it and your chin. Also notice if the corners of your mouth sort of "turn down" when your teeth are closed all the way together and your lips are sealed. Do either or both lips seem to lack the support they should have? When you look at your whole face, does the lower one third of it look too short relative to the other two thirds? If you see any of the things mentioned in this paragraph, then the odds are extreme that you could benefit from a more ideal vertical dimension.
The good news is that there is usually no good reason why the jaws can't be developed to their ideal size and position, both in adults (regardless of age) and children. This can be done non-surgically and with little or no discomfort. Vertical dimension can also be restored which will give you a much younger appearance, and if done properly, may eliminate any TMJ dysfunction symptoms from which you may be suffering.