TMJ Anatomy and Function

Temporomandibular Joint (TMJ) Anatomy

• The TMJ is a synovial joint formed by the mandible and temporal bone.
• It's located in front of the ear, on the side of the face.
• The joint's articulating surfaces include the mandibular fossa and articular tubercle (temporal bone) and the head of the mandible.

TMJ Structure and Function

• The joint has a unique structure: an articular disc separates the bones, creating two synovial cavities.
• The surfaces of the bones are covered with fibrocartilage, not hyaline cartilage.

TMJ Movements

• Protrusion/Retraction: The upper part of the joint.
  • Protrusion is driven primarily by the lateral pterygoid (and medial pterygoid).
  • Retraction is facilitated by the posterior temporalis muscle fibres.
• Elevation/Depression: The lower part of the joint.
  • Depression is primarily gravity-assisted.
  • Muscles like the digastric, geniohyoid, and mylohyoid aid with depression against resistance.
  • Elevation is a more forceful movement, caused by the temporalis, masseter, and medial pterygoid muscles.

TMJ Blood Supply and Innervation

• Blood supply comes from branches of the external carotid artery (superficial temporal, deep auricular, ascending pharyngeal, and maxillary branches).
• Innervation is via the auriculotemporal and masseteric branches of the mandibular nerve (CN V3).

Clinical Relevance: TMJ Dislocation

• Dislocations can happen due to facial blows, yawning, or forceful biting.
• The mandible head "dislocates" out of the mandibular fossa, pulling forward.
• This makes it difficult to close the mouth.
• Facial and auriculotemporal nerves may be injured in severe dislocations.
• Posterior dislocations are extremely rare and usually require significant force to pass the postglenoid tubercle and overcome strong intrinsic ligaments.