Anatomy of the Temporomandibular Joint

The temporomandibular joint is the articulation between the skull and the mandible. It is a non load-bearing joint that facilitates opening of the mouth. The socket, making up the base of the skull is called the Glenoid Fossa and the ball component is the mandibular condyle. Just in front of the TMJ is a bony protrusion called the articular eminence. Between the condyle (ball) and Glenoid fossa (skull base), lies an articular disc responsible for creating a low friction environment between the two surfaces. To achieve opening, the condyle must under go two distinctly different movements. The first is simple rotation, where the ball stays withing the glenoid fossa and rotates about a horizontal axis.The second and arguably the most important part of opening is translation. Translation involves the condyle sliding forwards overt the articular eminence. During this movement the articular disc should be strictly adherent to the condyle, moving with the condyle during translation and opening. It should also remain attached to the condyle during closing.

Surrounding the bony structures and the disc is the joint capsule and joint ligaments. Outside of this are the muscles of mastication (chewing muscles). This group of muscles includes the Temporalis, Masseter, Medial and Lateral Pterygoid muscles. Commonly people with TMJ dysfunction have pain originating from the over use of these muscles (myofascial pain). Pain that is located (Often on both sides) to temporal regions, the cheeks and the corner of the jaw is myofascial pain. Pain that locates immediately infront of the ear canal is temporomandibular joint pain. It is often associated with clicking, popping, grating, limited mouth opening and needing to deviate the jaw or push it to one side to obtain opening. These signs often indicate internal derangement exists.

Classification of TMJ Disorders

TMJ disorders are frequently divided into four categories

  • Myofascial Pain
  • Internal Derangement
  • Degenerative Disorders
  • Growth Disturbances and Asymmetry

Myofascial Pain

Originates from the muscles of mastication including the temporalis, masseter, medial and lateral pterygoid muscles.The pain from these muscles can be well localized or radiate to the temporal region, angle of the jaw, ear and neck. Often described as dull, aching and constant. This pain is often made worse by eating chewy foods. It is frequently worse in the morning if bruxism (Grinding) is the cause. This disorder is multifactorial meaning there are multiple issues contributing to the disorder. The most common causes are personal habits, stress and bruxism. As with any muscle if it is exercised, it will hypertrophy resulting in increased size (bulk) and tension (tone). This constant overuse results in a persistently fatigued muscle, the build up of lactic acid and pain, similar to a work out at the gym. This can occur in isolation to a single muscle or to all muscles involved in closing the jaw. As with any muscle that is over used, stretching, massage, heat therapy and Non-Steroidal Anti-Inflammatories (NSAIDS such as ibuprofen) are helpful in relieving this pain.

Treatment Options

Occlusal therapy (Bite Splint) and physiotherapy assist by elongating the muscles during sleep, this results in reduced tone when not using the splint, protects the teeth from wear and retrains the resting position of the jaw. We work with specific clinicians, technicians and physiotherapists experienced in the treatment of this condition and may refer you to them for an occlusal splint, physiotherapy or both. 

Botulinum therapy (Commercial names include Botox or Dysport) is a minimally invasive, temporary treatment modality that can assist in breaking the cycle of clenching, muscle hypertrophy, increased muscle tone and pain. It is used to block the transmission of nerve impulses attempting to cause contraction of the muscle. Its peak onset is approximately 2 weeks after injection and has a therapeutic affect for 3 months (approximately). Botox is excellent if there is obvious muscle hypertrophy (increase in size) of the temporalis and masseter muscles. As these muscles are reduced in size most people find an improvement in pain and notice reduced bulkiness at the angles of the lower jaw.

Internal Derangement

Internal derangement is a term that encompasses any abnormality within the joint capsule that results in altered function of the components of the temporomandibular joint. People with internal derangement can have no pain and function completely normally. An example is clicking of the joints without pain or a limitation in opening. The most common form of internal derangement is clicking of the joints which is normal in a large percentage of the population. Clicking inside of the joint arises from the sudden movement of the articular disc from a displaced position in front of the mandibular condyle to a position between the condyle and the articular eminence (normal position). Sometimes the term reciprocal clicking is used and indicates the disc clicks into the normal position on opening and clicks out of the normal position on closing. 

The position of the disc at rest is determined by the status of the disc (intact or perforated), the characteristics of the tissues that make up the anterior recess/joint capsule and the lateral pterygoid. In a small percentage of patients the lateral pterygoid muscle will insert into the anterior aspect of the disc. If this patient is known to suffer from bruxism, the hypertrophy and increased tone in this muscle can result in an anteriorly displaced disc. This not only positions the disc incorrectly but can stretch the retrodiscal tissues which contain nerve endings. As the disc is positioned anteriorly, this thin friable and sensitive retrodiscal tissue is pulled to a position between the condyle and the base of skull where the disc ideally should be. If a perforation occurs, this results in crepitus or the sensation of scraping or grinding when opening.

Treatment Options

Non Surgical If associated with bruxism or myofascial (common) a period of management with an occlusal splint, physiotherapy and/or botox may be appropriate.

Surgical Arthrocentesis of the TMJ can be performed under intravenous sedation. It involves passing 2 needles into the joint, including local anaesthetic to wash the joint space out. The increased pressure achieved stretches any scar tissue improving movement of the joint and allows the injection of steroids and hyaluronic acid. The steroids calm inflammation, reducing pain and the hyaluronic acid promotes cartilage integrity. The advantage of this procedure is excellent outcomes in respect to pain, low cost and is able to be performed as an outpatient. The major disadvantage is that it is a blind procedure, the joint space is not visualized and no instrumentation can be performed. Arthroscopic examination of the temporomandibular joint allows inspection of the anatomy, cartilage surfaces, articular disc and synovium (lining of the joint). Thanks to the miniaturization of instruments we can now perform procedures from inside of the joint. These procedures are commonly described as Level 1, 2 or 3 arthroscopy. Each level is associated with the use of an additional port and increased complexity.

Level 1 The first port allows visualization of the joint space and arthrocentesis (Irrigation and stretching of the joint space, capsule and any scar tissue present). An outflow port (Needle) is also placed facilitating the wash out of the joint which usually involved 300+ml of fluid.

Level 2 Allows instrumentation with a probe, laser and or coblation device allowing manipulation of the articular disc to see if it reduces, the release of scar tissue and scarification (targeted contraction) of tissue. Hyperplastic synovium, a source of inflammatory mediators responsible for pain can also be removed during a level 2 arthroscopy.

Level 3 The most difficult to perform and not always technically possible. This involves the insertion of 2 standard ports and 2 extra needles into the joint space. The first of the two needles passes from below, through the articular disc, the second needle is passed above the articular disc. A slow resorbing suture is then passed through the first needle and captured by the second needle. This allows suturing of the disc in a more normal position if it is intact. Each attempt to do this is more difficult than the previous attempt. Usually 1 or 2 sutures are able to be passed through the disc to secure it posteriorly.

Degenerative Joint Disease

The TMJ is susceptible to degenerative joint disease just like any other joint in the body. These processes historically were divided into high or low inflammatory states. This was a very broad way of separating that from wear and tear (Low inflammatory) and that from immune dysfunction such as Rheumatoid arthritis or infection (septic arthritis). Different people will have different rates of wear and tear. Collectively this is referred to, as osteoarthritis. It results in destruction of the cartilage within the joint responsible for covering the bone and creating a low friction environment. Once lost, no current therapy can replace it other than total joint replacement. Just as with hips, knees and shoulders, the temporomandibular joint can be replaced if function and pain are debilitating.

Growth disturbance and Asymmetry

These conditions are of low incidence, but are of high impact and often require orthognathic surgery after stabilization of the joints. Growth can be excessive or inadequate and it may be symmetrical or asymmetrical. The ball (Condyle) of the lower jaw is a major growth center of the face and any altered growth of the mandible can affect the maxilla (Upper jaw). It is not uncommon for the abnormal growth on one side to cause altered function and internal derangement on the other side. This area of maxillofacial surgery is complex and will be discussed in detail during your consultation. These conditions are important to be aware of as they frequently require an open joint procedure or total joint replacement.

Conditions associated with excessive growth

  • Condylar hyperplasia
  • Mandibular hyperplasia
  • Mandibular elongation

Conditions associated with insufficient growth or resorption

  • Idiopathic condylar resorption
  • Trauma / Condyle fractures
  • Inflammatory arthritis (Septic, Rheumatoid, Psoriatic, Idiopathic Juvenile arthritis)

Total Joint Replacement

Replacement of the temporomandibular joint occurs to relieve severe restriction in function and pain. Unlike a conventional hip or knee replacement composed of 'stock' or 'one shape fits all' components, a TMJ replacement is made specifically to fit the patient. A high resolution CT scan is 3D printed, surgery is then performed on the model allowing the construction and the manufacture of an implant that perfectly fits the patients anatomy. It comprises of two components, the first to replace the condyle (Ball), the second to replace the glenoid fossa (Socket).  These components are placed through two skin incisions. The first in front of the ear (pre-auricular),the second at the angle (Corner) of the mandible. There are risks and complications associated with this procedure and Mr Moore will discuss this in detail during your consultation.

Southern Cross Health Insurance AffiliateNew Zealand Medical CouncilAustralian and New Zealand Association of Oral & Maxillofacial SurgeonsRoyal Australasian College of Dental SurgeonsAHPRACanterbury District Health Board