Headahces. Jaw pain. Aching teeth. Stiff neck. Popping and clicking noises. Migranes. Anybody who suffers from jaw joint (TMJ) issues has had one or more of these symptoms. They can be aggravating, progressive, destructive, and sometimes even debilitating. My patients will ask, “It’s just one small joint, why does it cause so much trouble?” The answers they get, from various providers they’ve seen, can often be confusing, complicated, and conflicting. So let’s take a look at this mysterious joint and see if we can shed some light on why it causes so many problems for so many people.
The joint itself is pretty simple; the top of the mandible (lower jaw) forms a “head” and fits into a socket in the base of the skull, about 1cm in front of the ear. Between the head of the mandible and the socket is a cartilage disk that provides cushion and friction-free movement. Muscles attach to the mandible to move it in different directions (this is how we talk and chew), but muscles and ligaments also attach to the cartilage disk to try to keep it in the right position (like a “hat” sitting on the “head”) as the mandible moves around. When the head of the mandible is fully seated in the socket and the cartilage disk is properly between them, the TMJ is in its “happy place.”
Seems pretty simple, so how do things go wrong? It turns out the TMJ is rather unique in three key respects, and it is these unique attributes that can lead to trouble. First, the TMJ isn’t one joint, it’s actually two joints (the left and the right) operating on one bone. Since the skull and mandible are rigid, anything that happens in one joint directly affects the other. In an ideal situation, the two joints work in coordination to perform the jaw’s various functions, but the rigid connection between the two can often result in excessive and unnatural forces on one side or the other. For example, if you were to bite into something chewy on your right side, you might think this would put pressure on the right TMJ. In reality, the biting force is actually borne on the teeth on the right side, and it’s the left TMJ that has to shift out of its “happy place” while bearing the biting force.
The second difference is that the jaw joint actually performs two different movements. When you open slightly, the head of the mandible simply rotates in the socket. When you open fully, like when yawning, the head of the mandible actually slides down and forward; in other words, out of its happy place. This movement itself isn’t problematic, but this position is inherently unstable, and if a strong biting force is applied, the disk can get pulled out of position causing discomfort and damage.
Lastly, the mandible is the only bone that locks into a very specific position, i.e. when the teeth come together. Ideally, the teeth will fit together perfectly when the two TMJs are in their happy place. The problem is this is seldom the case. Teeth move and shift, sometimes intentionally with braces, sometimes all by themselves. The teeth themselves can change, such as when fillings or crowns are done, but sometimes just with wear or breakage. When changes like these occur the jaw then has to shift to get the teeth to come together comfortably, and the joints are then locked into an unnatural position.
I refer to this last issue as a bite discrepancy. And while all three items can certainly contribute to TMJ problems, a bite discrepancy is usually the one that starts the dominoes falling.
Part 2 will cover why this is and what to do about it.