The synovial joint connects two bones, the mandibular bone (lower jaw) and the temporal bone.
This complicated joint, along with its attached muscles, allows us to move the jaw up and down and perform side-to-side movements such as protrusion and retrusion.
This makes the movements necessary to speak, chew, yawn and make facial expressions possible.
The temporomandibular joint is a hinge that allows the jaw to move with the skull’s temporal bones.
These two joints are located just in front of each ear.
You can quickly locate this joint by opening and closing your mouth and feeling familiar with your fingers.
This joint differs from most joints, as it is called a diarthrosis joint; this type of joint has two joints that work independently, in this case, both the left and fitting jaw joints.
The temporomandibular joint is the most complex in the body.
Each person has two of them, one on the right side and one on the left, working together to provide movement of the jaw (lower jaw).
The temporomandibular joint is the only joint in the body built to be stable and unstable, as it is the only joint designed to pop out of its socket during function regularly.
It rotates inside the socket at the beginning of the opening but will slide out of the socket with a lateral movement or a vast space.
When there is a problem with the joints, muscles, or ligaments around this joint, the condition is often called a common temporomandibular disorder.
Temporomandibular joint anatomy
The temporomandibular joint is the joint between the condyle of the mandible and the squamous portion of the temporal bone.
The articular surface of the temporal bone is composed of the concave articular fossa and the convex articular eminence.
The meniscus is a fibrous, saddle-shaped structure that separates the condyle and the temporal bone.
The meniscus varies in thickness: the thinner central intermediate zone separates the thicker portions called the anterior band and posterior band.
Subsequently, the meniscus is contiguous with the posterior attachment tissues called the bilaminar zone.
The bilaminar zone is an innervated vascular tissue that plays a vital role in allowing the condyle to move forward.
The meniscus and its accessories divide the joint into superior and inferior spaces.
The superior joint space is limited above by the articular fossa and the articular eminence.
The inferior joint space is delimited by the condyle; both collaborative spaces have small capacities, generally one cc or less.
The temporomandibular joint is a type of modified hinge synovial joint made up of the condylar process of the mandible and the mandibular fossa of the temporal bone.
The surfaces of the joints are lined with fibrocartilage, which is unusual for a synovial joint; most are lined with hyaline cartilage.
The joint has a joint disc in the center of the joint socket.
The temporomandibular joint allows you to open and close your mouth and provides elevation, depression, protrusion, retrusion, and lateral jaw movements.
The ball in the socket that forms the temporomandibular joint is called the condyle.
It is the upper part of the jaw, on both sides, forming a rounded piece for the movement of the jaw.
High-impact injuries, autoimmune diseases, prolonged pressure, and inflammation can sometimes affect the integrity of this bone.
Arthritic changes in this bone will cause it to alter its shape, further affecting jaw movement and bite.
This is the socket of the temporomandibular joint. It is a bony cave under the temporal bone of the skull.
The condyle rotates within and slides forward of this socket.
Arthritic changes and injuries can also affect the mandibular fossa, causing shape alterations, jaw movement, and the bite.
The articular disc is a cartilage-shaped cushion between the ball and the socket. Its shape conforms to the ball and socket, allowing them to rotate and slide against each other.
The disc divides the temporomandibular joint into two compartments: an upper and lower joint cavity.
The disc is attached to the condyle on each side, to the muscles at the front, and to the rear of the socket using retrodiscal tissue.
The disc acts as a shock absorber and helps keep the movement smooth.
The disc can be damaged in many ways. It can shift, compress, tear, or shrink.
Damage to the disc can lead to TMJ problems and symptoms.
Upper and lower joint cavities
The disc divides these joint cavities, one above and one below.
They are filled with a joint fluid called synovial fluid, an exceptional fluid with properties to minimize friction and allow smooth movement of the parts of the temporomandibular joint.
Synovial fluid is believed to provide nutrition to the working surfaces of the joint.
The volume of fluid can change about barometric pressure and inflammation.
These can lead to jaw pain or bite changes.
The retrodiscal tissues are the tissues behind each disc of the temporomandibular joint.
These fabrics adhere to the socket by an upper band and are attached to the neck of the ball by the lower band.
The upper band is elastic, so it helps to keep the disc in its correct position.
The lower band does not have elastic fibers, so extreme stretching of this lower band sometimes causes injury or displacement of the disc.
The tissues between the bands contain most of the blood and nerve endings of the temporomandibular joint.
These tissues can be crushed in an unstable bite or clenching and grinding the teeth.
This leads to decreased blood flow. The swelling of the tissue is painful and can affect the bite.
The joint is separated into an upper and a lower compartment by the articular disc.
- The upper compartment is limited by the mandibular fossa of the temporal bone and by the articular disc. It contains 1.2 ml of synovial fluid and is responsible for the translational movement of the joint.
- The lower compartment has the articular disc as the upper border and the condyle of the mandible as the lower border. It is slightly smaller with an average synovial fluid volume of 0.9 ml and allows for rotational movements.
The temporomandibular joint capsule is the joint’s outer covering and seals it from the surrounding environment.
The inner layer has a membrane that provides fluid for lubrication, facilitating the function of the joint.
The capsule is fibrous, with one thick side forming a temporomandibular ligament.
The joint capsule originates from the edge of the mandibular fossa, encloses the articular tubercle of the temporal bone, and inserts into the neck of the mandible over the pterygoid fovea.
It is so loose that the jaw can naturally dislocate anteriorly without damaging the capsule fibers.
The fibrous cap has a thickened portion, called the lateral ligament, that strengthens the joint laterally.
The following ligaments support this joint:
- The medial and lateral collateral ligaments (also known as disc ligaments) help connect the medial and lateral sides of the articular disc to the same side of the condyle.
- The temporomandibular ligament extends from the temporal bone’s styloid process to the mandible’s angle. It is located on the lateral aspect of the capsule, and its function includes preventing lateral or posterior displacement of the condyle.
- The stylomandibular ligament arises from the styloid process and joins the mandibular angle. It is responsible for allowing the jaw to protrude.
- The sphenomandibular ligament runs between the spine of the sphenoid bone and the lingula of the mandible. It contributes to the limitation of extensive protrusive movements and the opening of the jaw.
These ligaments work together to guide and limit extreme movements of the lower jaw. These can be stretched or damaged with high-impact injuries to the face.
Three arteries supply the temporomandibular joint.
The main supply comes from the deep auricular artery (from the maxillary artery) and the superficial temporal artery (a terminal branch of the external carotid artery).
In addition, the joint is provided by the anterior tympanic artery (also a branch of the maxillary artery. Venous blood drains through the superficial temporal vein and the maxillary vein.
The mandibular nerve (third branch of the trigeminal nerve provides the primary nerve supply to the temporomandibular joint.
Additional innervation comes from the masseteric nerve and deep temporal nerves. The parasympathetic fibers of the otic ganglion stimulate synovial production.
Sympathetic neurons from the upper cervical ganglion reach the joint along the vessels and play a role in receiving pain and controlling blood volume.
The muscles that move the temporomandibular joint are called the chewing muscles. They include the following:
This muscle originates from the temporal fossa of the temporal bone. It is innervated by the mandibular nerve (CN V3) and raises and retracts the mandible.
This muscle originates from the lower and medial part of the maxillary process of the zygomatic bone and the zygomatic arch.
It is inserted at the angle of the mandible and the lateral part of the ramus of the mandible. It is innervated by the mandibular nerve and elevates the mandible.
The lateral pterygoid muscle is one of the central positioning muscles of the temporomandibular joint.
It is divided into an upper and a lower head, which originate in two places: the upper head originates from the greater wing of the sphenoid, and the lower head originates from the lateral pterygoid plate of the sphenoid bone.
The upper head attaches to the joint capsule and joint disc. The lower head inserts into the condyloid process of the mandible.
The lateral pterygoid muscles protrude (move forward) the jaw when the left and right are contracted together.
When a lateral pterygoid contracts, it moves the jaw to the contralateral side.
The upper muscle has fibers that adhere to the ball and the disc, helping stabilize their position with each other.
The lower head is more significant and pulls on the ball to allow opening, thrusting, and lateral movements of the jaw.
These muscles can be asked to work overtime on an unstable joint system. Muscle cramps, pain, and fatigue can occur.
This muscle also has two heads. One head originates from the lateral pterygoid plate and the pyramidal process of the palatine bone, and the other head originates from the maxillary tuberosity.
Both heads attach to the medial part of the ramus of the mandible. It is innervated by the mandibular nerve and works with the masseter to elevate the mandible.
The normal function of the temporomandibular joint
When the mouth is opened, there are two different movements in the joint.
The first movement is rotation about a horizontal axis through the condylar heads. The second movement is translation.
The condyle and meniscus move together anteriorly below the articular eminence. In the closed mouth position, the thick posterior band of the meniscus is immediately above the condyle.
As the condyle moves forward, the thinner medial area of the meniscus becomes the articulated surface between the condyle and the articular eminence.
When the mouth is fully open, the condyle may be under the anterior band of the meniscus.
Temporomandibular joint dysfunction
The internal temporomandibular joint disorder is present when the posterior band of the meniscus moves forward in front of the condyle.
As the meniscus is translated anteriorly, the posterior band remains in front of the condyle, and the bilaminar area is abnormally stretched and attenuated.
The displaced posterior band will often return to its normal position when the condyle reaches a certain point. This is called anterior displacement with reduction.
When the meniscus is reduced, the patient often feels a popping or popping sound in the joint.
The meniscus remains anteriorly displaced in the entire mouth opening in some patients. This is called anterior displacement without reduction.
Non-reduced anteriorly displaced patients often cannot fully open their mouths.
Sometimes there is a tear or perforation of the meniscus. Grinding noises in the joint are often present.
Problems associated with the temporomandibular joint muscles or jaw movements are called temporomandibular common disorders or dysfunctions.
These can cause difficulty opening the mouth, chewing, and general jaw movements.