Location and Anatomical Landmarks
The head of the mandible (Caput mandibulae) is located at the superior extremity of the ramus of the mandible (Ramus mandibulae).
- Condylar process (Processus condylaris) — the bony structure terminating in the head.
- Neck of the mandible (Collum mandibulae) — the constricted part supporting the head. Its medial surface features the pterygoid fovea (Fovea pterygoidea).
- Mandibular notch (Incisura mandibulae) — a concavity separating the condylar process with its head from the coronoid process (Processus coronoideus).
Role in the Temporomandibular Joint (TMJ)
The mandibular head forms the joint together with the mandibular fossa (Fossa mandibularis) of the temporal bone.
- Incongruity: The sizes of the head and the mandibular fossa do not match, creating intra-articular instability. Consequently, joint stabilization relies entirely on dental occlusion and the tone or status of the muscles of mastication.
- Articular disc (Discus articularis): A biconcave plate composed of dense fibrous tissue that bridges the mismatch between the articular surfaces. The inferior surface of the disc mirrors the shape of the mandibular head.
- Bilaminar zone: A connective tissue structure connecting the posterior part of the articular surface of the head to the posterior wall of the fossa.
Movements in the lower compartment of the joint cavity occur between the inferior surface of the disc and the mandibular head. In adults, the volume of synovial fluid in the lower compartment is 0.5–0.8 mL.
Biomechanics of Movements
The TMJ is a paired joint; therefore, movements of the mandibular heads on both sides occur strictly simultaneously.
- Mouth opening: This process is divided into three phases. In the first phase, the head rotates around the frontal axis in the lower joint compartment. In the second phase, it glides forward and downward together with the articular disc along the posterior slope of the articular tubercle, shifting anteriorly by approximately 12 mm (and up to 2 cm in some cases). In the third phase, at maximum mouth opening, movement occurs exclusively in the lower joint compartment around the frontal axis, with the articular disc resting on the articular tubercle.
- Lateral excursion: Movements are asymmetrical. On the working side, the head rotates around a vertical axis passing through the neck of the condylar process and shifts backward and medially. On the balancing (non-working) side, the head and disc glide downward, forward, and medially, reaching the crest of the articular tubercle.
Clinical Significance: Dislocations and Displacements
- Anterior dislocation: During excessive mouth opening, the head may slip anteriorly beyond the articular tubercle into the infratemporal fossa. Reduction methods include conservative techniques (such as Hippocrates', Blechman's, Gershuni's, and Popescu's methods) or manual manipulation: applying downward traction via the mandibular notch while simultaneously pressing the chin posteriorly.
- Posterior dislocation: Results from a direct blow to the chin from anterior to posterior while the mouth is open. The head is displaced posteriorly and becomes locked between the mandibular fossa and the mastoid process.
- Articular disc subluxation: During maximum mouth opening, the mandibular head fails to translate out of the mandibular fossa. Instead, anterior displacement of the disc occurs followed by repositioning, accompanied by a characteristic clicking sound.