Wednesday, June 15, 2011

The Anatomy of The Temporomandibular Joint

Dem Bones.

TMJ is really the hinge that allows us to open and close our jaw. However,we commonly refer to any pain or dysfunction in the hinge as TMJ or TMD (Temporomandibular Dysfunction).  Right now we are just looking at the anatomy of the temporomandibular joint .


Let us start by taking a look at the bony structure of the TMJ or temporomandibular joint.  There are two TMJ joints, one on each side of the skull.  The name comes from the two bones that make up the joint.  One is the bone on the side of the skull called the temporalis bone and the second is the lower jaw bone which is called the mandible. Hence the name temporomandibular joint.  These joints are located just in front of your ears.  These joints are nothing more than hinges which allow us to open and close our jaw.
Between the Bones.

Surrounding the TMJ joint is a capsule of fibrous material.  Between the bone joint is a special disc which is an extension of the capsule called an articular disc which is formed from a flexible, tough yet elastic tissue called fibrocartilage  Our ears are made up of this fibrocartilage.  This thin disc divides the joint into two cavities.  When the joint is in motion or there is pressure on the articular disc it releases synovial fluid into the cavities and this fluid acts like a shock absorber and reduces friction.  There is only one other place in the body that require an articular disc and that is where the top of the sternum, clavicle and first rib all meet.  At first, when you open your mouth a rotational movement occurs with the lower jaw and the disc but when you open the mouth even wider there is a second movement called the translational or forward and downward sliding movement of the disc and the jaw.  The two ends of the mandible or jaw are called condyles which comes from the word ”condyloma” which is derived from the Greek word ”kondylos” which means a knuckle or a knob. Further, “condyle” refers to a rounded articular surface.  This knob or condyle butts up to the underneath side of the TMJ disc.  On the mandible the glenoid or mandibular fossa meets the upper side of the disc and is a depression or concave-shaped.
Joining It All Together.
Ligaments are strong, tough, rope-like connective fibres. They connect bones to each other and connect cartilage to joints.. There is one primary and two secondary ligaments of the TMJ.  The temporomandibular ligament is the primary ligament which consists of two parts; the outer oblique portion or OOP and the inner horizontal portion or IHP.  The two minor or secondary ligaments are the stylomandibular ligament and the sphenomandibular ligament of which neither is directly attached to any part of the temporomandibular joint.
During movement only the jaw moves. Muscles attached to the bones and joints allow a variety of movements.such as yawning, chewing, talking, singing, shouting and swallowing, making the temporomandibular joints the most flexible in the human body. These sophisticated joints can move up and down and side to side in a wide range of motion and in a normal healthy jaw there is no pain or discomfort with these movements.

Muscles and The Nerve of It All.
The four muscles of mastication move the jaw or mandible.  They are the masseter, the medial pterygoid, lateral pterygoid and the temporalis.  The Trigeminal nerve is the sensory nerve for the face and the motor nerve for the mastication muscles  As the name suggests, the trigeminal nerve is made up of three branches.  The ophthalmic V1, sensory, the maxillary V2, sensory and the mandibular V3,motor and sensory branches.
TMJ Disorders, Pain and Discomfort.
Muscle fatigue from clenching the jaw or grinding your teeth, arthritis, and jaw injury are some of the causes of TMJ disorders. Understanding the anatomy of the joint will help you to better understand the workings of the TMJ and how surrounding bones,ligaments, nerves.and muscles can be affected when you experience temporomandinbular disorder.

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