TMJ facts and fiction

The subject of "TMJ" can be very controversial among the dentists. There are several "camps" or schools of thought based on what theories dentists were taught about jaw joint problems.  I realized soon after graduating dental school that I needed a better understanding of how teeth bite together and function (known as occlusion) in order to become an effective dentist.  I wanted to learn how teeth work together in harmony to in order to prevent the dental work I did from causing discomfort or excess biting pressure.

Therefore, I took continuing education courses from Dr. Peter Dawson and faculty in St. Petersburg Florida.  Through these courses and Dr, Dawson's book, I got a better grasp of how occlusion works.  I found that Dr. Dawson's theories agreed with the basic anatomy I learned in dental school. His treatment recommendations seemed well though-out, and practical and I was able to adapt them into how I practice dentistry every day.

Over the years of speaking with patients and colleagues, I have noticed that there are a lot of differing opinions about the causes of TMJ problems and how they should be treated. Therefore, I wanted to address some of the basics about "TMJ", as I understand it here.

1. Everyone has "TMJ" - Technically everyone has 2 TMJs which refers to your jaw joints, the Temporomandibular Joints.  The correct term for speaking about problems with the jaw joints is TMD or Temporomandibular Joint Dysfunction.

The mandible

Glenoid Fossae found behind Zygomatic arch/cheekbone.

The Temporomandibular Joints consist of several components:The concave areas found on the right and left of the base of the skull are called the mandibular or glenoid fossae.

• Projections on the top of the lower jaw or mandible are called the condyles.  The right and left condyles fit into the glenoid fossae.  
• Each condyle and fossae have a disk made of cartilage between them. The disk acts like a shock absorber and because of its slippery surface, assists the condyle in moving back and forth in the joint.    
• There are ligaments that attach the back and sides of the disk to the top of the condyle and help it stay in position as the condyle moves in the joint.  There is also a ligament that attaches from behind the condyle (mandible) to the maxilla. This ligament limits the motion of the jaw. 
• Chewing muscles- These muscles attach the mandible (jawbone) to the maxilla (top of the skull).  They flex and relax which allows the jaw to open and close for chewing and talking etc.  Elevator muscles flex and cause the jaw to close.  Depressor muscles flex and cause the jaw to open. In proper function, these muscle groups work opposite of each other.  For example, when the elevators are active, the depressors relax and vice versa. When the TMJs are properly aligned, the muscles work together with coordinated movements.

Diagram of elevator muscles in action causing teeth to bite and jaw seated fully in the socket.

2. The Temporomandibular Joints work in a unique way.  -Even though the joints on the right and left side of the skull are separate, they work together because the condyles are connected by the body of the mandible/jawbone.  In addition, the TMJs work by rotating and gliding. Where as most other joints in the body work only one way. When both condyles are fully seated in their sockets (glenoid fossae), the jaw can rotate open about 20 mm.  If the jaw rotates open more than 20 mm, the ligament that attaches the condyles of the mandible to the maxilla stretch to their limit and force the condyles to glide forward down the glenoid fossae.  This allows the jaw to open fully while preventing the airway behind it from being compressed (a very useful adaptation).

TMJ closed, open, disk displaced.

3.What is TMD,Temporomandibular Joint Dysfunction?-TMD is defined as pain and dysfunction of the chewing muscles and Temporomandibular joints (the joints which connect the mandible to the skull). This may be accompanied by restricted jaw movement and noises (popping, clicking, grinding) from the Temporomandibular joints (TMJ) during jaw movement. Depending on the how advanced the problem is, patients may experience from mild to debilitating pain.

Common complaints I hear from patients experiencing TMD are:

• Tenderness in the jaw joints with chewing or talking.
• Sore chewing muscles, especially in the morning.
• Grinding or clenching of the teeth, sometimes during sleep.
• Jaw locking open or closed.
• Frequent headaches.
• Difficulty opening.
• Popping or clicking noises from the jaw joint(s).

Diagram of muscle hyperactivity due to a crown causing an interference.

4. What causes TMD, Temporomandibular Joint Dysfunction? -The most common causes of TMD are as follows:
Misaligned bite- Teeth are designed to fit and function together in a specific way.  Ideally when the teeth bite together, the jaw joints should be able to seat all the way in the sockets. This occurs when the elevator muscles flex and pull the mandible upwards, and the depressors relax.  If the teeth are not aligned properly, a tooth (or a few teeth) may be slightly higher than the others, which is known as an interference.

Excess biting force on an interference (high tooth) can cause pain. So just as when you have a rock in your shoe,you adjust your steps to avoid stepping on the rock, your chewing muscles adjust your jaw position to prevent you from pounding on the high tooth.  This adjusted jaw position prevents the jaw from seating fully in the sockets when the teeth bite together.  Due to reflexes, chewing muscles may sense a high tooth and try to "grind it down". Unfortunately the single high tooth cannot be ground down alone so usually all teeth wear. This habit of teeth grinding or clenching in response to a misaligned bite is called bruxing. It also can make the jaw muscles feel overworked, tired, and painful.  Prolonged contraction of specific depressor muscles also causes the disk to be pulled out of position and deformed overtime.  The patient may then experience popping, clicking, or grating noises in the jaw joint as a result of the disk displacement.

Sometimes dental work can unintentionally introduce an interference by making a tooth or teeth higher than the others.  Problems can also arise with the bite when supporting teeth are extracted and not replaced. This is why it is important that the dentist have a good understanding of a patient's occlusion prior to doing dental work.

Trauma- a blow to the jaw can cause changes in the patient's bite.  Damage can occur to the disk, ligaments, mandible, and other structures and cause TMD.  The details of what actually can occur in the jaw joint as a result of trauma are too extensive to be covered adequately here.  For those who wish to learn more about this subject, I recommend reading Dr. Dawson's textbook, Functional Occlusion from TMJ to Smile Design .  I used this textbook and Dr. Dawson's training manual The Concept of Complete Dentistry (Seminar I) as a reference for this post.

*Stress- Stress is a factor and can cause symptoms to worsen especially if stress causes the patient to grind or clench their teeth more than usual.  However stress is not the original cause of TMD.  Patients who grind or clench their teeth only do so if they have interferences in their bite. A patient who's bite is free of interferences does not normally brux whether they have stress, or not.  A lot of people are taught that stress causes bruxing and are advised to "try to relax".  Unfortunately their TMD may go un-diagnosed and untreated for years due to this kind of advice.

5. How is TMD treated?- I was trained to take a verbal history of TMD patients' jaw joint problems.  I also learned how to listen to jaw joints using special equipment called a TMJ Doppler.  Based on the sounds, I can estimate where damage has occurred in the joint depending on when the joint makes noise with movement.  Images such as MRIs-magnetic resonance images and Cone Beam Computerized Tomography images are also helpful to see the extent and location of damage to the TMJs.  I use palpation to check for sore chewing muscles and ligaments.  In addition, I look for interfering teeth and am able to analyze the patient's bite.  I use all this information to customize treatment recommendations based on the level or severity of damage to the jaw joints.  People are often unaware that TMD can worsen in some patients if left untreated.  Therefore early diagnosis and intervention are important.

Occlusal Splint

An occlusal splint is often the first line of treatment for patients with mild to moderate TMD.  A splint is a clear, plastic, removable appliance that fits over the biting surfaces of the teeth.
The dentist adjusts the splint so that the bite is balanced (all teeth touch evenly).  The splint prevents interferences from keeping the teeth from sliding around freely.  The balanced bite on the splint also helps shut off the chewing muscle reflex that causes most patients to brux.  If a patient does continue bruxing (there is a small percentage who will brux regardless), they will only damage the acrylic and the teeth or supporting bone.  Therefore an occlusal splint is a good, non-permanent option to treat patients with TMD.  However it is not indicated in some patients with acute, severe disease.

For patients with minor interferences in their bite, an occlusal equilibration, may help to alleviate problems with TMD.  First a study is performed to see how severe the bite is misaligned.  Once it is determined that only minimal adjustments to tooth structure or restorations are needed to eliminate interferences, a occlusal equilibration is done.  This consists of selective grinding of teeth and restorations to eliminate high spots.  Sometimes restorations or missing teeth need to be replaced to accomplish this.  Many patients report feeling their jaw muscles relax and soreness in teeth subside after having their teeth properly equilibrated.

Teeth marked with occlusion paper to see interferences.

Occlusal equilibration.

Some patients with severely misaligned teeth may need orthodontics, also known as braces, to move the teeth so that their bite is even.  It is important to work with an orthodontist that plans cases with the goal of ensuring that the jaw joints can seat fully in the socket when the teeth bite together.  Unfortunately, some patients begin to have issues with TMD because their teeth were moved orthodontically to positions that do not allow this to occur.  They often report having headaches, sore teeth, and bruxing after their braces were removed.

In the most extreme cases, some TMD patients may have to have surgical intervention to repair damage to their jaw joint.  These patients are often in acute, debilitating pain and have very limited mobility of the jaw.  In my opinion, these cases should only handled by surgeons who specialize in TMJ surgery.

Hopefully this post has given some clarity on the causes of Temporomandibular Joint Dysfunction and the treatment options available.  Patients experiencing these problems should not hesitate to alert their dentist and seek help so that their problem does not get worse.  A solution can often be found to help stabilize the patient's TMD if it is caught soon enough.  If you have any further questions regarding this subject, feel free to contact Dr. Lisa Curry via email at info@currydentalcenter.com

Happy Smiling!