What is TMJ? Technically, it stands for "temporal mandibular joint." It is not the name of a jaw joint problem or disease. Although when someone has dysfunction of that joint(s) it is commonly called TMJ.
The TMJ or temporomandibular joint is located on each side of the head just slightly anterior and inferior to the ear canal.
It connects the lower jaw (mandible) with the temporal bone of the skull. Hence the name temporo-mandibular joint.
The joint moves in a hinge and gliding type of motion.
With the beginning stage of motion (opening) the condyle of the mandible pivots or rotates within the glenoid fossa of the temporal bone. As the jaw opens widely the condyle then glides in a forward motion and moves out of the fossa.
The joint surfaces are protected by a disc pad that allows for a smooth motion. With opening and closing of the mouth or mandible the motion should be performed in a smooth equal manner.
When there exists a problem of the TMJ joints it is often commonly referred to as "TMJ." However, as stated earlier, TMJ literally stands for the name of the joint -- temporal-mandibular joint.
The proper name for the problem of the TMJ should be referred to as TMD or TMJD. Meaning temporal mandibular dysfunction or temporal mandibular joint dysfunction.
The mandible is designed to move in a forward and backward motion called protrusion and retrusion respectively and in a side to side motion known as lateral excursion.
The four primary muscles involved in these motions are:
These muscles are paired; meaning, they are each present on both sides of the head.
The lateral pterygoid acts to open the mouth by pulling the condyle forward.
The other three muscles, medial pterygoid, massiter and temporalis, are responsible for closing the mouth by pulling the jaw upward.
During the act of chewing these muscles are all in play and are responsible for the varied motions needed during the act of mastication or chewing.
When the jaw (tmj) is at rest the lips are together but the teeth are not. If the teeth are clenched or touching during rest this is abnormal.
With normal TMJ mechanics there should be no deviating side to side during opening and closing of the mouth. Nor should there be any popping or clicking sounds.
If either of these two conditions exists (deviation in a lateral side to side movement, or popping or clicking sounds) this is abnormal and called dysfunction or TMJD.
The motion should be pain free, as the discs are free of nerve endings and so is the cartilage that covers the bone joint surfaces.
With an abnormal TMJ, when the mandible's condyle glides beyond the disc a clicking or popping sound can often be heard. As it returns to a normal position back onto the disc a popping sound is again heard.