The temporomandibular joint (TMJ) 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 undergo two distinctly different movements. The first is simple rotation, where the ball stays within 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 over the articular eminence. During this movement the articular disc should be strictly adherent to the condyle, moving with the condyle during translation and opening and it should also remain attached to the condyle during closing.
Surrounding the bony structures and the disc are 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 pterygoid muscle and lateral pterygoid muscle. Commonly people with TMJ dysfunction have pain originating from the overuse of these muscles (myofascial pain). Pain that is located in the temporal regions, the cheeks and the corner of the jaw is myofascial pain. This is often on both sides. Pain located immediately in front of the ear canal is TMJ 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 indicates that internal derangement exists.
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 localised 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 it. 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 workout at the gym. This can occur in to a single muscle in isolation or to all muscles involved in closing the jaw. As with any muscle that is overused, stretching, massage, heat therapy and non-steroidal anti-inflammatories (NSAIDS such as ibuprofen) are helpful in relieving this pain.
Occlusal therapy (Bite Splint) and physiotherapy assist by elongating the muscles during sleep. This results in reduced tone for times when the splint is not being worn, 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 and 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 blocks the transmission of nerve impulses attempting to cause contraction of the muscle. Its peak onset is approximately two weeks after injection and has a therapeutic erffect for three 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 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 without 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 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. This 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 and 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 that 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 also 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.
Non-Surgical If associated with bruxism or myofascial (common) a period of management with an occlusal splint, physiotherapy and/or botulinum toxin may be appropriate.
Surgical Arthrocentesis of the TMJ can be performed under IV sedation or general anaesthetic. 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 the fact it is sometimes able to be performed as an outpatient procedure. The major disadvantage is that it is a blind procedure, the joint space is not visualised and no instrumentation can be performed. By comparison, 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 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 visualisation 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 300ml or more 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 two standard ports and 2 extra needles into the joint space. The first of the two needles passes from below, through the articular disc, and 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 the disc to be sutured in a more normal position if it is intact. Each attempt to do this is more difficult than the previous. Usually one or two sutures are able to be passed through the disc to secure it posteriorly.
The TMJ is susceptible to degenerative joint disease, just like any other joint in the body. Historically, these processes were divided into high or low inflammatory states - 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.
These conditions are of low incidence, but high impact and often require orthognathic surgery after stabilisation of the joints. Growth can be excessive or inadequate, and it may be symmetrical or asymmetrical. The condyle (ball) 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 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.
Replacement of the temporomandibular joint is performed to relieve severe restriction in function and severe 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 and an implant is constructed and manufactured to fit the the patient's anatomy perfectly. It comprises of two components; the first to replace the condyle (ball), and 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 these in detail during your consultation.
