Understanding the Temporomandibular Joint (TMJ) and its Disorders
Introduction
The temporomandibular joint (TMJ) is a crucial joint that connects your jawbone to your skull. Located in front of the ear, it plays a vital role in speaking, chewing, and other jaw movements. This article delves into the anatomy, function, and common disorders of the TMJ.
Articulating Surfaces
The TMJ is a complex joint formed by the articulation of three surfaces:
- Mandibular fossa: A depression in the temporal bone.
- Articular tubercle: A rounded prominence on the temporal bone.
- Head of the mandible: The condyle of the jawbone.
Unlike other joints, the bony surfaces of the TMJ don’t directly contact each other. Instead, they are separated by an articular disc, dividing the joint into two synovial cavities. This unique structure allows for smooth and complex movements of the jaw.
Ligaments
Three main ligaments provide stability to the TMJ:
- Lateral ligament: Connects the articular tubercle to the mandibular neck, preventing posterior dislocation.
- Sphenomandibular ligament: Runs from the sphenoid bone to the mandible.
- Stylomandibular ligament: A thickening of the parotid gland fascia that supports the jaw’s weight.
Movements
The TMJ facilitates a wide range of jaw movements, orchestrated by the muscles of mastication and the hyoid muscles.
- Protrusion and Retraction: The upper part of the joint allows the jaw to move forward (protrusion) and backward (retraction). The lateral pterygoid muscle is the primary muscle responsible for protrusion, while the geniohyoid and digastric muscles retract the jaw.
- Elevation and Depression: The lower part of the joint enables the opening and closing of the mouth. Gravity primarily causes depression, assisted by the digastric, geniohyoid, and mylohyoid muscles when resistance is encountered. Elevation, a powerful movement, is achieved by the contraction of the temporalis, masseter, and medial pterygoid muscles.
Neurovasculature
- Arterial Supply: The TMJ receives its blood supply from branches of the external carotid artery, mainly the superficial temporal artery. Other contributing arteries include the deep auricular, ascending pharyngeal, and maxillary arteries.
- Venous Drainage: Veins accompanying the arteries drain the joint.
- Innervation: Sensory innervation to the TMJ is provided by branches of the mandibular nerve (CN V3), specifically the auriculotemporal and masseteric nerves.
Disorders of the Temporomandibular Joint
Dislocation
TMJ dislocation occurs when the head of the mandible slips out of the mandibular fossa, usually due to a blow to the face, excessive yawning, or taking a large bite. This condition prevents mouth closure and can potentially damage the nearby facial and auriculotemporal nerves. While rare, posterior dislocations can occur with significant force.
Arthritis
Arthritis can affect the TMJ, leading to inflammation and symptoms like jaw stiffness and a grinding sensation during movement.
