Temporomandibular Joint Dysfunction
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ANATOMY OF THE TMJ
The temporomandibular joint (TMJ) is a ginglymoarthrodial joint, a bilateral synovial articulation between the condyle of the mandible and the squamous part of the temporal bone (glenoid fossa or mandibular fossa). An articular disc lies between the condyle and fossa.
The TMJ is composed of the joint capsule (capsular ligament), articular disc, mandibular condyle, articular surface of the temporal bone, temporomandibular ligament, stylomandibular ligament, sphenomandibular ligament, and lateral pterygoid muscle.
The concave articular surface of the temporal bone is covered in dense fibrous (fibrocartilaginous) connective tissue. Anterior to the glenoid fossa is the convex articular eminence.
The articular disc is a dense fibrocartilaginous (not hyaline like other synovial joints) connective tissue that lacks vascular and neural infiltration (only the very periphery is slightly innervated). The cartilage of the mandible condyle is a secondary fibrocartilage, compared to the articular cartilage found in other joints, formed by intramembranous (not endochondral) ossification after the bones are already formed. Compared to hyaline cartilage, fibrocartilage is better able to withstand the shear forces generated by the occlusal load placed on the TMJ.
Synovial fluid provides nutrients for this area. It has a biconcave structure between the two convex surfaces of the articular eminence and the mandibular condyle. The intermediate zone is thin, the anterior and posterior bands thicker. The anterior band of the articular cartilage attaches to the capsular ligament, lateral pterygoid muscle and the condyle. Tanslational (gliding) movement occurs primarily in the superior joint space, rotational (hinging) movement occurs primarily in the inferior joint space.
The posterior bands connect with the retrodiscal tissues which is loose connective tissue, highly vascular and innervated by nerves from the auriculotemporal branch of the mandibular division of the trigeminal nerve. The anterior region of the TMJ is innervated by the masseteric nerve and the deep temporal nerve (also branches of V3).
MUSCLES OF MASTICATION
The muscles of mastication are the four muscles primarily involved in the adduction (masseter, temporalis, lateral and medial pterygoid) and abduction (lateral pterygoid) of the mandible. The suprahyoid and infrahyoid muscles are indirectly involved in mandibular movement. Most of the facial muscles are innervated by the facial nerve (or CN VII), but the muscles of mastication are innervated by the mandibular branch of the trigeminal nerve (CN V).
- Temporalis – originates in the floor of the temporal fossa deep to the temporal fascia, inserts along the coronoid process and the anterior border of the ramus of the mandible. Functions to elevate and retrude the mandible.
- Masseter – the superficial portion originates from the anterior two-thirds of the lower border of the zygomatic arch, the deep portion originates from the medial surface of the zygomatic arch. The masseter inserts along the lateral surface of the ramus and angle of the mandible, as well as the coronoid process. Functions to elevate, retrude and protrude the mandible.
- Lateral pterygoid – the superior head originates in the infratemporal surface of the greater wing of the sphenoid bone. The inferior head originates from the lateral surface of the lateral pterygoid plate. The lateral pterygoid inserts in the anterior portion of the condylar neck and the anterior TMJ capsule. Functions to protrude the mandible, to depress the mandible, as well as lateral movement of the mandible.
- Medial pterygoid – the superficial head originates from the maxillary tuberosity. The deep head originates from the medial surface of the lateral pterygoid plate. The medial pterygoid inserts on the medial surface of the ramus of the mandible inferior to the mandibular foramen. Functions to protrude and elevate the mandible, as well as lateral movements of the mandible.
ACCESSORY MUSCLES & LIGAMENTS
The Accessory muscles to the muscles and the muscles of mastication work together in a coordinated fashion, and they include the buccinator, suprahyoid muscles and infrahyoid muscles.
Suprahyoid muscles are located above the hyoid bone. The digastric, stylohyoid, and mylohyoid muscles are all pharyngeal muscles. The digastric has two bellies connected by an intermediate tendon that slings through a connective tissue hoop attached to the hyoid bone. In general they elevate the hyoid and open esophagus for swallowing, and depresses the mandible when the hyoid bone is fixed (by the infrahyoid muscles).
- Anterior belly of the digastric – originates on the digastric fossa of the mandible, insert into the intermediate tendon, functions to elevate the base of the tongue and the hyoid bone.
- Posterior belly of the digastric – originates on the mastoid notch, inserts into the intermediate tendon, functions to elevate the base of the tongue and the hyoid bone.
- Geniohyoid – originates on the inferior mental spine/genial tubercle on the inner surface of the mandibular symphysis, inserts into the anterior surface of the hyoid bone, functions to elevate the hyoid.
- Mylohyoid – originates along the mylohyoid line that extends from the last molar to the mandibular symphysis, inserts into the median raphe from the chin to the hyoid bone, functions to elevate the base of the tongue, floor of the mouth and hyoid bone.
Recall centric relation (CR) is the most stable, reproducible mandibular position in relation to the base of the skull. It is defined as the most anterior and superior position of the mandibular condyles within the glenoid fossa (mandibular fossa) of the temporal bone. While in CR, only rotational movement can occur. It’s a ligament-guided position.
There are 5 ligaments associated with the TMJ.
- Temporomandibular ligament – also called the lateral ligament, 2 short bands from the zygomatic arch to the lateral surface and posterior border of the neck of the mandible. Prevents posterior displacement and lateral reinforcement for the capsule. It is the main stabilizing ligament of the TMJ.
- Sphenomandibular ligament – spine of sphenoid to the lingula of the mandible. Limits max opening.
- Stylomandibular ligament – styloid process of the temporal bone to the angle of the mandible. Prevents extreme protrusion.
- Capsular ligament – surrounds the TMJ.
- Lateral ligament – reinforces the anterior lateral wall preventing excessive lateral movement and posterior displacement.
There are 4 arteries that vascularize the TMJ.
- Middle meningeal artery (maxillary artery).
- Ascending pharyngeal artery (external carotid).
- Deep auricular artery (maxillary artery).
- Superficial temporal artery (external carotid).
TEMPOROMANDIBULAR DISORDER (TMD)
Temporomandibular disorder (TMD) is defined as a group of disorders involving the masticatory muscles, the temporomandibular joint (TMJ), and the associated structures. Sign and symptoms can vary, and may include:
- Joint noises – clicking (crepitus).
- Locking open (cannot close fully) or locking closed (cannot open fully).
- Pain or muscular tenderness in the head, neck and shoulders.
- Ear complaints – otalgia, tinnitus.
Clicking or crepitus is not necessarily due to pathology. In the absence of pain and dysfunction you only need to monitor a patient presenting with crepitus. Examination of the TMJ includes a thorough medical history. The joints are palpated looking for tenderness which would indicate inflammation. Palpating the lateral aspect of the joint while the patient opens and closes is useful for assessing pain, crepitus and deviations. Palpating the anterior wall of the external auditory meatus will provide information on the posterior aspect of the TMJ. The range of motion in all dimensions can be analyzed. Magnetic resonance imaging has been accepted as the current gold standard for imaging of the TMJ.
TMJ disorders can arise from many different areas. Myofascial pain dysfunction (MPD) syndrome is characterized by muscle spasm, pain, and dysfunction. Pressure to sensitive points on muscles causes pain. This syndrome is related to excessive use caused by repetitive motions associated with certain jobs/hobbies. Stress-related muscle tension can cause MPD. It is the most common form of TMJ pain.
Disc displacement disorders describe abnormal relationships between the disc, condyle, and mandibular fossa. It is often associated with synovial inflammation and joint overloading, also referred to as Internal derangement . The posterior band of the articular disc becomes displaced anteriorly in relationship to the condylar head, overloading the innervated and vascular retrodiscal tissue. The resulting joint inflammation leads to reduced synovial fluid production and poor joint lubrication.
Anterior displacement with reduction refers to the displaced posterior band of disc able to return to its anatomically correct position. When it reduces, the patient often experiences a click or pop. Anterior displacement without reduction sees the disc unable to return to its correct anatomical position. The patient is unable to open all the way, and if unilateral, deviation will be seen to the affected side. There is no clicking or pop.
TMJ dislocation occurs when the mandibular condyle becomes trapped in front of the articular eminence. Spasming of the muscles of mastication causes pain and holds the condyle in this abnormal position. Treatment involves manual manipulation of the joint into its correct position. Local anesthesia or sedation may be required to overcome the strong muscular reflex. Placement of fingers on the external oblique ridge area prevents you from losing them.
Degenerative Joint Disease sees arthritic changes inside the synovial joint. Rheumatoid arthritis (RA), psoriatic arthritis (PA), and ankylosing spondylitis (AS) have an affinity towards the TMJ. Systemic lupus erythematosus (SLE) can affect the TMJ. The disease process is different from those seen in osteoarthritis (degeneration) or following trauma (leading to ankylosis). Rheumatoid arthritis leads to inflammation with granulation tissue, then erosion of cartilage and bone. Osteoarthritis can exhibit hardening of the cartilage, sclerosis of subchondral bone, cracking/fissuring/dislodging of pieces into synovium, and bony degradation.
Signs and symptoms of degenerative joint disease include
- Chronic pain
- Rheumatoid arthritis involves many joints, degenerative arthritis may be limited to the TMJ.
- Rheumatoid pain is usually worse in the morning, degenerative pain is generally worse later in the day.
- Rheumatoid factor, increased ESR, and latex fixation is seen in RA.
TMD TREATMENTS
TMD treatments can be classified as reversible or irreversible therapy. Reversible therapies include:
- Patient education – avoid triggers like clenching, grinding, nail biting etc.
- Medication – NSAIDs, steroids, tricyclic antidepressants, muscle relaxants.
- Splint therapy – oral splints or mouth guards designed to reduce joint load. Anterior repositioning splints protrude the mandible.
- Physical therapy – exercise and stretch musculature. Ultrasound, heat, ice, transcutaneous electrical nerve stimulation (TENS), iontophoresis etc.
If no relief is found or the patient has trouble managing the side effects of medications other available treatments include:
- Arthrocentesis – minimally invasive procedure that involves the insertion of a small needle into the superior joint space so that fluid can be irrigated through the joint to remove debris and inflammatory byproducts.
- Injections – corticosteroid injections into the joint may be helpful. Botulinum toxin type A (Botox) into the surrounding musculature may relieve pain.
- TMJ arthroscopy – a thin cannula is placed into the joint space and an arthroscope inserted along with a small surgical instrument. The risk of complications is lower compared to open joint surgery but the operation is limited.
- Modified condylotomy. Increases the joint space by allowing the mandibular condyle to move inferiorly with respect to both the articular disc and eminence. The condyle is vertically segmented along with half the body and part of the angle, allowing the vertical repositioning of this distal segment.
- Open-joint surgery – the most invasive and risky surgical option, to repair or reposition the disc, or replace the joint. Usually done in the case of ankylosis. A preauricular incision is commonly used. A submandibular incision (Risdon incision) is used when access to the angle of the mandible, ramus or lower part of the condyle is sought (not joint). In close proximity to the TMJ are the branches of the facial nerve and trigeminal (auriculotemporal) nerve, as well as the superficial temporal artery and vein, the maxillary vein, the maxillary and transverse facial artery, pterygoid venous plexus, and the parotid gland with intraparotid lymph nodes.
There are no definitive studies that suggest malocclusion causes TMJ. Some treatment options have questionable efficacy, or relatively high levels of risk. These include:
- Occlusal adjustments.
- Orthognathic surgery.
- Orthodontic treatment.
- Prosthetic restoration.
