**Abstract**

Temporomandibular joint is an important bilateral synovial joint of body. This chapter focuses on the basic anatomy of TMJ and its disorders. Any pain or symptom of TMJ falls under the category of temporomandibular joint disorder. There is a decade old debate of cause-effect relationship of malocclusion and temporomandibular joint disorder. How orthodontic treatment can positively contribute to this problem is highlighted in this chapter.

**Keywords:** temporomandibular joint disorder, orthodontics, malocclusion, anatomy

## **1. Introduction**

The temporomandibular joint is the joint that joins lower jaw (mandible) to the skull. It is a bilateral synovial joint formed between the articular surface of temporal bone and condylar head of the mandible. The functioning of the joint is together and not independent of the other. The main components of the joint are the capsule, disc, articular surface of temporal bone, temporomandibular ligament, stylomandibular ligament, sphenomandibular ligament, and lateral pterygoid muscle [1].

The articular capsule (capsular ligament) is a thin loose envelope, attached above to the mandibular fossa and the articular tubercle below. The disc is a dense fibrocartilage positioned between the mandibular fossa and the articular surface of the head of condyle. This synovial joint is divided into two compartments by the disc *viz.* upper and lower joint compartment. Capsule's synovial membrane fills these compartments with synovial fluid and provides lubrication. The central area of the disc is avascular with no innervation, and synovial fluid nourishes the disc. The posterior ligament and the surrounding capsule have both blood vessels and innervation. The central area is thinner and of denser consistency; peripheral is thicker and cushioned. Age-related changes may thin the disc and add cartilage to the center and may lead to impaired movement of the joint. Disc is a fibrous extension of the capsule between the two bones, and is biconcave and attached to the condyle medially and laterally. Anterior portion of the disc divides backward vertically and continues as retrodiscal tissue; forwardly, the split becomes coincident with the superior head of lateral pterygoid. The lower joint compartment allows the rotational movement, while opening and upper joint compartment allows translation.

TMJ has three ligaments: one major and two minor ligaments. Ligaments define the extent of movement of mandible. If movements go beyond the extent allowed by muscles, pain will arise. Major ligament, the temporomandibular ligament is in reality, thickened lateral portion of the capsule. It has two parts: an outer oblique and an inner horizontal portion. This ligament is shaped like a triangle with base attaching to the zygomatic process of temporal bone and articular tubercle, and apex at lateral side of the neck of the mandible. This ligament prevents the retraction/distal movement of the mandible and thus protects the joint. The rest of the minor ligaments sphenomandibular and stylomandibular ligaments are not attached to the joint. Stylomandibular ligament runs from the styloid process to the angle of the mandible and becomes tight on mandibular protrusion. Sphenomandibular ligament, a remnant of Meckel's cartilage, runs from the spine of sphenoid to the lingula of mandible, which also becomes tight with mandibular protrusion. Other ligaments are otomandibular, discomallear, and malleomandibular ligament.

**Blood supply**: Superficial temporal branch of external carotid artery majorly innervates the joint.

**Nerve supply**: Auriculotemporal and masseteric branches of mandibular branch of trigeminal nerve provide sensory innervation to the TMJ. Proprioreception occurs through four receptors: Ruffini endings, Golgi tendon organs (static), Pacinian corpuscles (dynamic), and free nerve endings (pain). Free nerve endings are present in the bones, ligaments, and muscles except the fibrocartilage).
