Patients can sometimes develop a serious problem with their jaw, which if left untreated, can adversely affect the teeth, gums and bone structures of the mouth. One of the most common jaw disorders is related to a problem involving the temporomandibular joints (two), the joints that connect your lower jaw to your skull, and allows your upper and lower jaw to open and close and facilitates chewing and speaking.
The two joints function continuously together night and day. When we eat, sneeze, yawn, speak, and swallow (the average person swallows 1,000 times per day) this joint is getting used. Add to this any unusual habits such as chewing gum, chewing pens, grinding your teeth, tapping your teeth, cheek biting, etc. it adds up to a lot of use. The TMJ is unlike any other joint in that there are two that work in harmony with the other. Its anatomy is different as well.
Unlike a typical hinge joint such as the knee or elbow, the TMJ has a larger complex range of motion. Measuring the space between the upper and lower front teeth, most patients can open 40-60mm wide. In the first 10-15mm, the joint functions mostly like a hinge, but beyond that the joint goes into translation where the head of the condyle slides down and forward out of the temporal fossa and down the eminence. When the jaw is moved to the left or right, the condyle on the opposite side slides down and forward along the eminence. Facilitating these movements is a sickle shaped disk that sits between the condyle and fossa. It travels with the condyle during translation and movement down the eminence.
Most of the tissue surrounding the TMJ are several ligaments. Like all other ligaments, they do not repair well if at all when damaged.
There are four pairs of muscles (temporalis, medial pterygoid, later pterygoid, and masseter) that are involved with moving and stabilizing the jaw. The temporalis muscle is located on the side of the head starting from in front of the ear and fanning out toward the top of the head and look much like a hand held fan. This muscle is the muscle is the primary muscle that works to close the jaw until resistance is met. It also functions to move the jaw to the left and right, back ward, and to a lesser extend forward. The masseter and medial pterygoid are the two powerhouse muscles. These two muscles do not fire (contract) until the teeth come in contact with a hard bolous of food or each other. It has been shown that when these muscles fully contract, they can generate up to 300-500 pounds of pressure per square inch.
The lateral pterygoid is a small muscle that sits horizontally in front of the joints. This muscle is the only muscle of mastication that is involved in opening the jaw, is the only muscle that has any attachment to the disk, it is involved in moving the jaw forward and from left to right, but it is also believed to help stabilize the disk when clenching and during translation.
The platysma muscle extends like a curtain from the lower border of the lower jaw and extends down the front of the neck. This muscle along with the mylohyoid, digastric, and genihyoid function to open the jaw as well.
This complex joint system also has one other aspect to function with…. the teeth. Whe jaw closes, there must be a harmony between the position of the joints, the tonicity of muscles, and the occlusion (matching) of the upper and lower teeth.
Understanding this system and how they work together and influence each other is crucial in diagnosing dysfunction.
Temporomandibular Joint Disorder or Dysfunction (TMD) usually refers to discomfort or disruption of function with the joints and associated muscles. A large majority of the population has or has had (possibly from time to time) “TMD”. Some of the more common symptoms are clicking, popping, or crunching sounds in the joints as well as headaches.
Crepitus is a word used to describe a “crunching” or “grinding” type noise in the joints during function. It is found in more than half the population and is considered normal wear and tear.
Clicking or popping is most often associated with the disk and can be of little concern or the sign of significant structural damage. A good history and evaluation is necessary to understand what might be happening. Most often, there may be an occasional pop when yawning or eating. Moderate pain may be associated. Again depending on a patients history, definitive treatment may not be necessary.
It is reported that 95% of all TMD cases are musculature in nature while the others directly involve the joint with some being more serious such as improperly aligned joints or dislocated jaws. This is not to suggest that muscles are the most common cause, but where symptoms begin to surface. Headaches and facial pain are often one of the more compromising symptoms in our experience.
Proper diagnosis of TMD is important and not always easy. Proper treatment can not be provided without a solid understanding of the underlying cause.
The following factors must be considered in a comprehensive history and evaluation:
A fall, auto accident, sports, eating, etc. can be cause for minor and sometimes severe injury of the TMJs. For most minor injuries, rest is the best treatment, however you can only limit their use so much, unlike using a crutch to allow a sprained ankle to heal. Most often a soft diet, NSAIDs, limit opening wide, and possibly occlusal splint therapy can allow for proper healing.
Many people clench and grind their teeth on a daily basis, and some may find that they only do so during times of stress or strenuous activity. This can cause muscle strain and fatigue that can result in headaches and facial pain.
Occlusion (how the teeth come together and match up) requires much attention and focus. The roots of teeth are surrounded by nerve endings that are highly sensitive. When the teeth are brought together, they can detect a difference of 25 microns (the width of a hair). Newly placed dental restorations, injury, and tooth loss are some examples of changes that can alter the feel of a patients occlusion or “bite”. Such a small discrepancy can trigger muscle response to “find the bite”. The muscles struggle to align the jaw in order to evenly distributed contact to mostly the posterior (back) teeth. This almost always causes over working of the lateral pterygoids and parts of the temporalis muscle. Because the temporalis muscle is so accessible and palpatable, trigger points can be easy to find. Depending on the location of occlusal discrepancies, there can be multiple trigger points in different areas. Once these points are found, they can often times be very sore and painful. Gentle massage of these areas can bring instant relief as well as opening wide to slightly stretch those fibers. Non-steroidal anti-inflammatories (NSAIDs) and moist heat also work well to help relieve this tension. Ultimately, however, these only treat the symptoms and not the cause.
Proper occlusion is more than just the teeth coming together evenly. How they come together as the jaw moves is just as important. When a patient bites down and brings their back teeth together it is often referred to as centric occlusion or habitual centric. From this position any movement side to side or forward and backward is considered and excursive movement. The points of the back teeth and edges of the front teeth are there to guide the jaw in movement (often called working contacts) allowing the front teeth to protect the back teeth and vice versa, but there are movements when some points and edges should not contact (non- working contacts or occlusal interferences).