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What is the TMJ?

TMJ is the abbreviation for temporomandibular joint. Everyone has two of these joints, and the term “TMJ” refers to the normal, healthy joint on each side of the skull that allows the lower jaw to function during speech, swallowing, and chewing. The name of the joint comes from the two bones that make up each side of the joint. Like all joints, the TMJ is made of muscle, ligaments, cartilage, and bone with supporting nerves and nutritional supply in the form of synovial fluid.

The temporal bones of the skull form the “roof” and “inside” of the TMJ, and the mandible (lower jaw) makes up the floor of the joint, which moves in three directions: It rotates around an imaginary axis for the first part of the opening stroke of the jaw and the last part of the closing stroke; it translates , or slides, down and forward from the endpoint of rotation to maximum jaw opening; and, it moves side to side. Specifically, the part of the mandible that is involved with the TMJ is called the condyle, and the part of the temporal bone involved in the joint is called the temporal fossa. Because the TMJ moves in three planes of space, unlike all other joints in the body that move like a hinge, the TMJ is called a ginglymoarthroidal joint. Between the two bones is a cartilaginous disc that serves as sort of a shock absorber to protect the joint that slides with the condyle during the range of motion. Attaching to the disc and the mandible is a specific muscle, called the lateral pterygoid that pulls the disc and the jaw forward as the jaw translates. There also ligaments that hold the disc to the condyle on each side of the disc, called collateral ligaments.

TMJ

This model represents a healthy TMJ showing the disc (blue) properly positioned between the condyle and temporal fossa. The muscles shown are the main jaw closing muscles.

A discussion of the TMJ is not complete without mentioning that the mandible is essentially a bone floating in space. In fact, when ancient skulls are discovered in archaeology, the mandibles are usually absent because the soft tissue has all been lost, allowing separation of the mandible from the skull.

This means that the function, health, and stability of the TMJ is totally dependent on the supporting muscles and ligaments of the head and neck and the teeth that provide a stop at the right place for optimal chewing strength.

The masseter muscles, the temporalis muscles, the digastric muscles, the medial pterygoid muscles, and the lateral pterygoid muscles are the primary muscles involved in jaw function. Since these muscles all work by pulling on the bones of the skull, it is important to consider that the skull is like a bowling ball balancing on a broken broomstick, which is the spine. This balancing act requires harmony in function of many supporting muscles of the upper back, neck, chest, and shoulders. Therefore, it is easy to understand how many problems of the head, neck, and upper back can manifest themselves as TMJ problems; sometimes, TMJ problems can also present as dental problems, neck pain, headaches, etc. Often, the term “TMJ” is incorrectly used to refer to a problem that does not easily fit another diagnosis by the medical community.

VIDEO: TMJ Disorder


 

What is TMD?

When any part of the anatomical structures or supporting structures of the TMJ is injured or damaged, dysfunction occurs. While “TMJ” refers to the temporomandibular joint itself, “TMD” refers to temporomandibular disorder. TMD syndrome is a vague term that usually involves one or more conditions listed below and/or others not mentioned:

  • TMD

    This model represents and injured TMJ where the disc (blue) is displaced and the condyle is degenerating.

    Capsulitis

  • Tendonitis
  • Myofascial pain
  • Myositis
  • Myalgia
  • Osteoarthritis
  • Degenerative Joint Disease
  • Retrodiscitis
  • Tinnitis
  • Headaches of various types
  • Dislocation of the disc
  • Subluxation of the disc
  • Muscle spasm
  • Cervicalgia

TMD Treatment

Treatment for TMD is dependent on the specific diagnoses involved and is typically directed to resolving pain rather than reducing joint noises (popping, clicking, etc.). Joint noises are evidence that injury has occurred and are signs rather than symptoms. Pain, compromised quality of life, and compromised function, however, are symptoms that treatment is typically directed toward.

Treatment for TMJ disorders is controversial, and clinicians often differ in their approach. Some tend to treat physically (physical therapy, bite splint therapy, chiropractic, etc.), some tend to approach treatment from a medical model (medications, mental health therapy, etc.), and some practice the philosophy that TMD tends to be self-limiting and opt not to treat but rather provide supportive care only.

The reality is that successful management of TMD usually involves elements of each approach and often requires a team approach involving some or all of the following healthcare providers: dentist, mental health specialist, family physician, physical therapist, chiropractor, massotherapist, orofacial pain specialist, oral surgeon, etc.

Because TMD is often a chronic pain disorder, compromises in mental health in the form of depression, anxiety, psychosomatic conditions, all of which may require the assistance of a psychiatrist.

Dentists often use bite splints to treat TMD syndrome

The type of splint used should be dependent on a specific diagnosis of a specific condition. For this reason, different types of splints may be used at different times during the treatment of TMD. In fact, splints may actually also be used for diagnostic purposes to rule out complicating factors.

VIDEO: Bruxism

One of the factors that can contribute to pain that may be a part of temporomandibular joint disorders and that is often considered under this group of conditions is bruxism, which involves clenching and/or grinding of the teeth outside of normal chewing function.  Bruxism may be due to problems with breathing, a side effect of medications, or some type of nervous disorder or habit.  Bruxism can lead to broken teeth, receding gums, joint pain, and bone loss.  Treatment may include protective bite splint therapy and/or bite adjustments to stabilize the teeth when under abnormal function, and sometimes treatment for sleep disordered breathing may be indicated.

CT scan of TMJ

CT scan of two TMJs

The images in the bottom row shows a relatively normal TMJ with early joint degeneration; the top row shows a degenerated joint with flattening of the condyle.

Headaches

Headaches come in many forms and in different degrees. Every day, more is learned about what causes them and how they can be prevented. Hormones, abnormal growths, abnormal signals from the brain, syndromes, and muscle function are just some of the causes. Usually, treatment and prevention of headaches requires a team of health professionals including physicians, physical therapists, psychologists, and even dentists.

Some dentists are trained in treating jaw joint problems, some are trained in treating headaches, and some choose not to treat these ailments in their particular practices for one reason or another. However, if you suffer from headaches and have been treated unsuccessfully by physicians who have ruled out any medical problems, you might consider discussing it with your dentist. He or she may be able to help you or refer you to someone who could.

Since many headaches are caused by long-term spasming of some of the jaw and neck muscles, some types of “nightguards”, or bite splints, may be used to help provide relief. Essentially, these variations of acrylic platforms provide a stable place for the jaws to close against which does not allow the jaw muscles to contract to their maximum force.

It has been estimated that approximately 80% of people clench and/or grind their teeth during sleep, and many of these people develop “tension headaches” related to it.

Bite Splints & Nightguards

Custom-fit Athletic Mouthguards

This is one type of bite splint that is appropriately made out of soft materials

Athletic mouthguards should only be used to protect the teeth during athletic events from blows to the chin. Since the most important part of a mouthguard is where it covers the farthest back tooth in the mouth, a dentist should always be involved in the selection of an appropriate mouthguard.

nightguard
Tanner type bite splint

Therapeutic Bite Splints

Also known as oral orthotic appliances, are custom-made of hard plastic and intimately fit the teeth, typically to manage TMJ problems, some types of headaches, and bite issues.

There should not be significant movement of the bite splint. The way the teeth fit together on top of the plastic is specific to the diagnosis being treated, and usually several adjustments and modifications are necessary for effective therapy. Whether bite splints are made to fit the upper teeth, the lower teeth, or even both arches is based on the purpose of the treatment and clinician preference.

Fees for bite splints are actually for the therapy, not necessarily for the piece of plastic used. Sometimes, variations in the shape of the splint and the amount of teeth that are covered are indicated, depending on the purpose for the splint.

VIDEO: Occlusal Appliance for Tooth Wear

Nightguards

Many dentists provide “nightguards” for patients who clench or grind, and there is a general understanding that they protect the teeth.

However, this is not necessarily true, and there are many different bite splint designs used for different purposes. Bite splints are therapeutic, if and only if they are properly made for the right reasons, with the appropriate design, and at the appropriate time in dental therapy.

Nightguards and athletic mouthguards are often made of soft thermoplastic materials, custom made by a dentist or even purchased over-the-counter.

The rationale is that a soft, rubbery material cushions the teeth and that they are economical. However, these materials can actually make muscle symptoms and headaches worse because they give the patient something to chew on, and they are not therapeutically stable. The result can be joint injury, loosening or fracture of teeth, and an increase in the frequency and intensity of tension-type headaches.

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