The Temporomandibular

joint

T.M.J

Dr. Haydar Muneer Salih

The temporomandibular joint (TMJ) is a modified hinge type of synovial joints, permitting gliding (translation) and a small degree of (rotation) in addition to flexion (elevation) and extension (depression) movements typical for hinge joints.

◦ It is composed of the temporal bone and the mandible, as well as a specialized dense fibrous structure, the articular disk, several ligaments, and numerous associated muscles.

Articulation occurs between the articular tubercle and the anterior portion of the mandibular fossa of the temporal bone above and the head (condyloid process) of the mandible below. The articular surfaces are covered with fibrocartilage.

Bony StructuresThe articular portion of the temporal bone is composed of the articular or mandibular fossa, a concave structure extending from the posterior slope of the articular eminence to the postglenoid process, which is a ridge between the fossa and the external acoustic meatus. The surface of the articular fossa is thin and may be translucent on a dry skull. This is not a major stress-bearing area.

The articular eminence◦ It is a transverse bony

prominence that is continuous across the articular surface mediolaterally. The articular eminence is usually thick and serves as a major functional component of the TMJ. The articular eminence is distinguished from the articular tubercle, a nonarticulating process on the lateral aspect of the zygomatic root of the temporal bone, which serves as a point of attachment of collateral ligaments.

Cartilage and Synovium

◦ Lining the inner aspect of all synovial joints, including the TMJ, are two types of tissue: articular cartilage and synovium. The space bound by these two structures is termed the synovial cavity, which is filled with synovial fluid.

The articular surfaces of both the temporal bone and the condyle are covered with dense articular fibrocartilage, a fibrous connective tissue. This fibrocartilage covering has the capacity to regenerate and to remodel under functional stresses.

The synovial membrane

◦ Is a thin, smooth, richly innervated vascular tissue without an epithelium Synovial cells, somewhat undifferentiated in appearance, serve both a phagocytic and a secretory function and are thought to be the site of production of hyaluronic acid, a glycosaminoglycan found in synovial fluid.

Synovial fluid

Is considered an ultrafiltrate of plasma. It contains a high concentration of hyaluronic acid, which is thought to be responsible for the fluid’s high viscosity The proteins found in synovial fluid are identical to plasma proteins Functions of the synovial fluid include lubrication of the joint, phagocytosis of particulate debris, and nourishment of the articular cartilage

Ligaments

◦ The lateral temporomandibular ligament strengthens the lateral aspect of the capsule, and its fibers run downward and backward from the tubercle on the root of the zygoma to the lateral surface of the neck of the mandible. This ligament limits the movement of the mandible in a posterior direction and thus protects the external auditory meatus

◦ The sphenomandibular ligament lies on the medial side of the joint . It is a thin band that is attached above to the spine of the sphenoid bone and below to the lingula of the mandibular foramen.

◦ The stylomandibular ligament

lies behind and medial to the joint and some distance from it. It is merely a band of thickened deep cervical fascia that extends from the apex of the styloid process to the angle of the mandible.

Capsule

The capsule surrounds the joint and is attached above to the articular tubercle and the margins of the mandibular fossa and below to the neck of the mandible.

The articular discIt is composed of oval plate of dense fibrous connective tissue and is nonvascularized and noninnervated, an adaptation that allows it to resist pressure. It is divides the joint into upper and lower cavities. It is attached circumferentially to the capsule.. The upper surface of the disc is concavoconvex to fit the shape of the articular tubercle and the mandibular fossa; the lower surface is concave to fit the head of the mandible

Blood supplySuperficial temporal, deep auricular and anterior tympanic arteries.Venous drainageSuperficial temporal and maxillary veins.Nerve SupplyAuriculotemporal, posterior deep temporal and masseteric branches of the mandibular nerve.

MUSCLES OF MASTICATIONTMJ movements are produced chiefly by the muscles of mastication. These four muscles (temporal, masseter, and medial and lateral pterygoid muscles) develop from the mesoderm of the embryonic first pharyngeal arch; consequently, they are all innervated by the nerve of that arch, the (motor root of the trigeminal ) mandibular nerve (CN V3). All muscles of mastication originate on the skull and insert on the mandible

The temporalis muscleis a large fan-shaped muscle taking its origin from the temporal fossa and lateral aspect of the skull, Its fibers pass between the zygomatic arch and the skull and insert on the mandible at the coronoid process and anterior border of the ascending ramus down to the occlusal surface of the mandible, posterior to the third molar tooth.

The temporalis muscle

◦ The function of the temporalis muscle is to elevate the mandible for closure. It is not a power muscle. In addition contraction of the middle and posterior portions of the temporalis muscle can contribute to retrusive movement of the mandible. to a small degree unilateral contraction of the temporalis assists in deviation of the mandible to the ipsilateral side

The masseter musclea short rectangular muscle taking its origin from the zygomatic arch and inserting on the lateral surface of the mandible, it is the most powerful elevator of the mandible and functions to create pressure on the teeth, particularly the molars, in chewing motions. The masseter muscle is composed of two portions, superficial and deep, which are incompletely divided, both the superficial and deep portions of the masseter muscle are powerful elevators of the mandible

The masseter muscle

but they function independently and reciprocally in other movements. The deep layer of the masseter is always inactive during protrusive movements and always active during forced retrusion, whereas the superficial portion is active during protrusion and inactive during retrusion.

The medial pterygoid muscle

is rectangular in shape and takes its origin from the pterygoid fossa and the medial surface of the lateral plate of the pterygoid process, with some fibers arising from the tuberosity of the maxilla and the palatine bone. Its fibers pass inferiorly and insert on the medial surface of the mandible, inferiorly and posteriorly to the lingual

The medial pterygoid muscle

The main function of the medial pterygoid is elevation of the mandible, but it also functions somewhat in unilateral protrusion in a synergism with the lateral pterygoid to promote rotation to the opposite side

The lateral pterygoid muscle◦ It has two portions that can be

considered two functionally distinct muscles.

◦ The larger inferior head originates from the lateral surface of the lateral pterygoid plate. Its fibers pass superiorly and outward to fuse with the fibers of the superior head at the neck of the mandibular condyle, inserting into the pterygoid fovea.

The lateral pterygoid muscle

◦ The superior head originates from the infratemporal surface of the greater sphenoid wing, and its fibers pass inferiorly, posteriorly, and outward to insert in the superior aspect of the pterygoid fovea, the articular capsule, and the articular disk at its medial aspect, as well as to the medial pole of the condyle

The lateral pterygoid muscle

◦ The primary function of the inferior head is protrusive and contralateral movement. The function of the superior head of the lateral pterygoid muscle is predominantly involved with closing movements of the jaw and with retrusion and ipsilateral movement

TMJ Dislocation

TMJ Ankylosis

TMJ Ankylosis