Temporomandibular Joint Anatomy

Temporomandibular Joint (TMJ)

• The TMJ is the joint connecting the mandible (lower jaw) to the skull.
• It's located in front of the ears on both sides of the head.
• It allows jaw movement for speaking and eating.
• It's a complex articulation between the mandible and the base of the skull.
• It's a bilateral synovial joint permitting movement in three planes.
• It's the only visible and free-moving articulation in the head; others are fixed.
• Jaw movements are controlled by reflexes.
• The TMJ plays a key role in speech and mastication.

Bony Landmarks of the TMJ

• Mandibular (glenoid) fossa: A depression in the temporal bone where the mandible sits.
• Articular eminence: The front part of the temporal bone, gentle slope, covered in cartilage. The mandibular condyle moves over this during jaw movement.
• Mandibular condyle: The rounded end of the mandible, covered by dense fibrous connective tissue with cartilage-like cells, allowing smooth motion.

Bones of the TMJ and their components

• Mandibular (glenoid) fossa:

  • A depression in the temporal bone of the skull.
  • Covered with cartilage for smooth jaw movement.
  • Dense cortical bone that thins at the roof.
  • Located posterior to the articular eminence.

• Articular eminence:

  • Located in front (anterior) of the fossa.
  • This gentle slope of bone is smooth and covered in cartilage.
  • The condyle moves over the eminence during jaw opening, side-to-side movements, or protrusion.

• Mandibular condyle:

  • Covered with dense fibrous connective tissue containing irregular cartilage-like cells.
  • This layer of cartilage enables smooth movement within the joint.

Other Components of the TMJ

• Articular capsule: A fibrous membrane surrounding the joint, attaching to the articular eminence, the articular disc, and the neck of the mandibular condyle.
• Synovial tissue: Connective tissue lining the inside of the joint capsule.
• Articular disc: A fibrous extension of the capsule that runs between the two articular surfaces of the TMJ. biconcave shape holding the condyle, articulates with the mandibular fossa above and the condyle below.
• Ligaments: Provide passive stability to the TMJ. Include the temporomandibular, stylomandibular, and sphenomandibular ligaments.

Movement of the Mandible

• The mandible moves in multiple ways including:
  • Depression and elevation (up and down)
  • Lateral deviation (side-to-side)
  • Protrusion and retrusion (forward and backward)
• On opening, the condyle initially rotates within the glenoid fossa.
• Rotational movement has multiple axes: horizontal, frontal, and sagittal.

Function of TMJ Ligaments

• Accessory ligaments limit the mandible's movement; the TMJ capsule and ligaments restrict extreme lateral movement during wide jaw openings.

Disorders of the TMJ

• Myofascial pain: Discomfort or pain in muscles controlling jaw function and neck/shoulder muscles; most common.
• Internal derangement: Dislocation or displacement of the jaw or articular disc/injury to the condyle.
• Degenerative joint disease: Osteoarthritis or rheumatoid arthritis in the jaw joint.

Symptoms of TMJ Disorders

• Headaches, migraines, earaches, pressure behind eyes.
• Clicking or popping sounds when opening/closing mouth.
• Pain from yawning, wide mouth opening, or chewing.
• Jaws "getting stuck" or locking.
• Jaw muscle tenderness.
• Change in upper and lower teeth fit.
• Limited opening ability (trismus).

Treatment for TMJ Disorders

• Exercises
• Heat
• Medications (pain relief, muscle relaxants)
• Botox
• Soft diet
• Orthotic appliances (bite guards/splints)
• Surgery (arthroscopy, arthrocentesis, join replacement)

Dislocated Jaw

• Symptoms: Facial/jaw pain worsening with movement. Bite feeling "off." Trouble talking. Inability to close mouth; drooling. Locked jaw or forward protrusion.

Jaw Relocation

• Doctors/dentists wrap fingers in gauze, placing thumbs inside the mouth on lower back teeth.
• Other fingers surround lower jaw.
• Pressing on back teeth and pushing chin up until jaw joints return to their normal location.

TMJ - Useful Links

• Various YouTube videos with information on TMJ anatomy, including relevant animations on TMJ disc displacement.

Trismus

• Trismus involves difficulty opening the mouth to more than 35mm.
• It may follow head/neck traumas, cancer treatments, oral surgery, infection, or result from local anesthesia.
• It can be temporary or permanent.

Additional information

• Diagrams and x-rays demonstrate normal and dislocated jaw positions.