Anatomy of the Temporomandibular Joint

Temporomandibular Joint (TMJ)

• The TMJ is a joint on each side of the head that allows for movement of the mandible for speech and mastication.
• The TMJ is the articulation between the temporal bone and the mandible.

Bones of the Joint

• The temporal bone is a cranial bone.
• The mandibular fossa or articular fossa is an oval-shaped depression on the temporal bone.
• The mandibular condyle is the articulating part of the mandibular ramus.
• The mandible is a facial bone.

Joint Capsule

• A fibrous joint capsule completely encloses the TMJ.
• The joint is supported by the joint capsule and several ligaments.

Disc of Joint or Articular Disc

• The articular disc is a fibrous pad of collagen tissue located between the temporal bone and the mandible.
• The disc completely divides the TMJ into two compartments: upper and lower.
• The synovial cavities are lined with epithelium, which secretes synovial fluid.

Structure

• The articular eminence is a smooth, rounded ridge positioned anterior to the mandibular fossa.
• The retrodiscal pad is composed of loose connective tissue supplying blood and nerves to the joint.

Ligaments Associated with the Joint

• Three paired ligaments are associated with the TMJ:
  • Temporomandibular ligament
  • Stylomandibular ligament
  • Sphenomandibular ligament

Temporomandibular Ligament

• Reinforces the lateral part of the joint capsule.
• Prevents the condyle from being displaced too far inferiorly and posteriorly.
• Prevents lateral displacement of the mandible.

Stylomandibular Ligament

• Runs from the styloid process of the temporal bone to the angle of the mandible.
• Separates the parotid and submandibular salivary glands.

Sphenomandibular Ligament

• Is not considered part of the TMJ.
• Helps control movement.
• Runs from the angular spine of the sphenoid to the lingual.
• Becomes taut when the mandible protrudes.
• May prevent diffusion of local anesthetic agents during an IA nerve block.

Movement in the TMJ

• The TMJ has two types of movement:
  • Rotational - occurs in the lower synovial cavity between the disc and the condyle.
  • Gliding - occurs as the jaw opens farther.

Gliding Movement

• Protrusion - anterior movement.
• Retrusion - posterior movement.

Rotational Movement

• Depression - lower the jaw.
• Elevation - raise the jaw.

Gliding and Rotational Movement

• Lateral Deviation - alternating protrusion and retrusion.
• Opening the mouth - protrusion and depression.
• Closing the mouth - retrusion and elevation.

TMJ Dysfunction (TMD)

• TMD may involve one or both TMJs.
• Symptoms include: chronic joint tenderness, swelling, painful muscle spasms, limited or deviated mandibular opening.

Assessing the TMJ for TMD

• Palpate the joint and its associated muscles bilaterally, just anterior to the external acoustic meatus of each ear.
• Ask the client to open and close the mouth, move the opened jaw left and right, and forward.

TMD

• Not all clients with TMD have abnormalities in the joint disc or the joint itself.
• Most symptoms originate from the muscles supporting the joint.

TMJ Sounds

• Clicking, popping, or grinding (crepitus) in the TMJ.
• Popping or clicking occurs when the disc is pulled too far forward on opening.
• If it pops on closing, it is called a "reciprocal pop or click."
• On palpation, the joint may "jump."
• The mandible may deviate/shift to one side on opening.

Disc Disengagement

• The cause of TMJ sounds may be the result of disc disengagement.
• In constant anterior displacement of the disc, permanent damage may occur.
• Treatment may require surgical intervention.

Trismus

• Inability to open the mouth normally.

TMJ Problem: Subluxation

• An acute episode of TMD can occur when the mouth opens too wide.
• The condyle glides too far forward and moves too far anterior to the height of the articular eminence.
• Contributing factors: deep condylar fossa, hypermobility, and muscle incoordination.

TMJ Problem: Bruxism

• Teeth grinding, typically during sleep, but some do it while awake.
• Causes tired and sore TMJ, wearing down of teeth.
• Treatment: night guard, relaxation medications.

TMJ Problem: Arthritis

• Inflammation and deterioration of the joint.
• Potentially caused by excessive wear of the joint.
• Treatment option: cortisone.

TMJ Problem: Myofascial Pain Dysfunction (MPD)

• Increased pain at the TMJ due to muscle tension and spasm.
• Believed to be a physical manifestation of psychological stress.
• No primary disorder of the joint itself is present.

TMD

• Most cases of TMD improve over time with conservative treatments, including pain control, relaxation therapy, stress management, habit control, moderate muscle exercises, and orofacial myology.