TEMPOROMANDIBULARJOINT

Temporo-Mandibular Joint /Craniomandibular Articulation

> Receives its name from the 2 cranial bones which enter into its formation,

1. temporal bone 2. mandible.

> It is closely associated with the role of teeth in the oral cavity.

Classification:

Diarthrosis Joint (Freely movable joint)

- one in which a fibrous capsule connects the 2 bones. A space is provided between the 2 bones which is lined by synovial membrane, thus allowing free movement of the joint.

Variety:

Ginglymoarthrodial - allows both hinge and gliding movements.

Consists of: a) Bone d) Synovial

b) Ligament membranec) Cartilage e) Muscles

A. Articulating Bony Parts:

1. Mandibular Fossa of the Temporal Bone/ Glenoid Fossa

- an oval depression in the temporal bone just anterior to the auditory canal

2. Condyloid Process/ Condylar Process/ Mandibular Condyle

- a knob-like bone (wider latero-medially than antero-posteriorly), it is convex on all bearing surfaces although somewhat flattened posteriorly.

3. Articulating Tubercle/ Articular Eminence

- bony elevation located anterior and posterior to the glenoid fossa or mandibular fossa.

Anterior Articular Eminence - anterior to the mandibular fossa- controls the forward movement of the condylar head

Posterior Articular Eminence- posterior to the mandibular fossa- controls the backward movement of the condylar head

B. Ligaments:

1. Capsular Ligament

- a synovial capsule which completely surrounds the condyle.

- Divided into 4 portions:

a) Anterior portionb) Posterior Portionc) Internal Portiond) External Portion / Temporomandibular Ligament

Temporomandibular Ligament

- largest portion

- acts as main suspensory ligament of the mandible during moderate opening movement (hinge).

- it has a broad attachment above the zygomatic process of the temporal bone, the anterior fibers attaching forward beyond the articular eminence & is inserted into the outer side and posterior margin of the neck of the condyle.

2. Sphenomandibular Ligament

- round & cordlike at its origin and takes more of a ribbon like form at its insertion.

- with wider opening of the jaw, the condyle move forward rapidly, relaxing the external lateral ligament as the sphenomandibular ligament becomes tensed or slightly stretched.

- originates from the spinous process of the sphenoid bone and inserts into the lingula of the mandible with some fibers attached below the mandibular foramen.

3. Stylomandibular Ligament

- extends from the styloid process of the temporal bone and inserts into the posterior border of the ramus of the mandible.

- just before the stylomandibular ligament makes its insertion, it gives off an accessory fiber which continue downward to the posterior border of the hyoid bone, called the stylohyoid ligament.

* the temporomandibular ligament & the sphenomandibular ligament acts as suspensory ligaments.

* the stylomandibular ligament & its accessory stylohyoid ligament acts as checkrein on the mandible and helps prevent excessive anterior drift at the angle during more extreme opening movements.

C. Cartilage

Meniscus – a tough fibrous disc also known as Interarticular Disc or Interarticular Fibrocartilage.

Cavities:

a) Menisco-Temporal Cavity - larger cavity- allows gliding of the condylar head to the articular eminence.

b) Menisco-Condylar Cavity- smaller cavity- allows hinge movement of the condylar head.

D. Synovial Membrane

- lines the internal surface of the meniscus.

- Synovial Fluid lubricates the articulating parts.

E. Muscles

Muscles of Mastication1) Masseter2) Temporalis3) Internal or Medial Pterygoid4) External or Lateral Pterygoid

Masseter

- is a flat, quadrangular muscle, partly tendinous, partly fleshy.

Origin:

Superior portion – anterior 2/3 of the lower zygomatic arch.

Deeper portion – whole length of deep surface of the zygomatic arch.

Insertion: on the lateral surface of the coronoid process, ramus & gonion.

Action: is to elevate the jaw with the superficial fibers causing protraction.

Temporalis

- is a large, fan-shaped muscle on the side of the head.

Origin: floor of the temporal fossa & temporal fascia.

Insertion: apex & deep surface of the coronoid process and along the anterior border of the ramus down to the last lower molar tooth.

Action:

Anterior fibers – elevate the mandiblePosterior fibers – retract the mandible

* anterior part acts as synergist with the masseter in clenching.

* posterior part may acts as antagonist to the masseter in retruding the jaw.

Internal or Medial Pterygoid

- is quadrilateral in shape.

Origin: from the medial surface of the lateral pterygoid plate, the posterior surface of the tubercle of the palatine bone and the tuberosity of the maxilla.

Insertion: is into the triangular impression on the medial surface of the mandible between its mylohyoid groove and the angle.

Action: is to elevate & protract the mandible. It also moves the jaw from side to side when acting singly.

External or Lateral Pterygoid

- is a thick and triangular muscle with two heads.

Origin: Superior portion – is from the

infratemporal surface of the great wing of the sphenoid.

Inferior portion – is from the lateral surface of the lateral pterygoid plate.

Insertion: the fibers are directed laterally and backwards into the front of the neck of the mandible & into the capsule of the TMJ.

Action: is to depress, protrude & move the mandible from side to side.