Temporomandibular joint

Articulatio temporomandibularis

Also known as: TMJ, jaw joint

The synovial joint between the head of the mandible and the mandibular fossa and articular tubercle of the temporal bone, divided by an articular disc into upper (gliding) and lower (hinge) compartments.

Overview

The TMJ is a modified hinge (ginglymoarthrodial) synovial joint. Unusually, its articular surfaces are covered by fibrocartilage, not hyaline cartilage (it develops from intramembranous bone). A biconcave fibrocartilaginous articular disc divides the cavity into a superior compartment, where the disc and condyle translate (glide) forward onto the articular tubercle, and an inferior compartment, where the condyle rotates (hinges) under the disc. The disc is attached posteriorly to a vascular, innervated retrodiscal tissue (bilaminar zone) and anteriorly to the lateral pterygoid (superior head).

Opening the mouth begins with rotation in the lower compartment (≈20–25 mm incisal opening) followed by forward translation of the condyle and disc onto the articular eminence for full opening (≈40–50 mm). The joint is reinforced by the lateral (temporomandibular) ligament and accessory sphenomandibular and stylomandibular ligaments. Movements: depression (lateral pterygoid, digastric, geniohyoid, mylohyoid, gravity), elevation (temporalis, masseter, medial pterygoid), protrusion (lateral and medial pterygoids), retraction (posterior temporalis), and side-to-side grinding.

Location

In front of the ear, between the mandibular condyle and the temporal bone.

Parts & subdivisions

Articular disc

Biconcave fibrocartilage; divides the joint into upper and lower compartments.

Upper compartment

Disc on the fossa/articular tubercle — translation (gliding).

Lower compartment

Condyle on the disc — rotation (hinge).

Mandibular fossa and articular tubercle

Temporal bone articular surfaces.

Condylar head

Mandibular articular surface.

Anatomy

Innervation

Auriculotemporal and masseteric branches of the mandibular nerve (V3).

Arterial supply

Superficial temporal and maxillary arteries.

Articulations

Head of the mandible ↔ mandibular fossa and articular tubercle of the temporal bone (with intervening disc).

Ligaments

Lateral (temporomandibular) ligament — main stabiliser, prevents posterior displacement; sphenomandibular ligament (spine of sphenoid → lingula); stylomandibular ligament (styloid → angle).

Clinical significance

TMJ dislocation

Usually anterior and bilateral: with excessive opening (yawning, dental procedures, seizures) the condyle slides in front of the articular eminence and is locked there by muscle spasm; the mouth cannot close. Reduced by downward and backward pressure on the lower molars.

Temporomandibular disorders

Pain, clicking (anterior disc displacement with reduction) and limited opening, often with bruxism and myofascial pain; pain may be referred to the ear because of the shared auriculotemporal innervation.