Januari 03, 2017
the temporomandibular joint -- the tmj - isthe joint between the lower jawbone - - the mandible - and the temporal bone of the skull.the tmj is responsible for jaw movement and is the most used joint in the body. the tmjis essentially the articulation between the condyle of the mandible and the mandibularfossa - a socket in the temporal bone. the unique feature of the tmj is the articulardisc - a flexible and elastic cartilage that serves as a cushion between the two bone surfaces.the disc lacks nerve endings and blood vessels in its center and therefore is insensitiveto pain. anteriorly it attaches to lateral pterygoid muscle - a muscle of chewing. posteriorlyit continues as retrodiscal tissue fully supplied with blood vessels and nerves.the mandible is the only bone that moves when
the mouth opens. the first 20 mm opening involvesonly a rotational movement of the condyle within the socket. for the mouth to open wider,the condyle and the disc have to move out of the socket, forward and down the articulareminence, a convex bone surface located anteriorly to the socket . this movement is called translation. the most common disorder of the tmj is disc displacement, and in most of the cases, thedisc is dislocated anteriorly. as the disc moves forward, the retrodiscal tissue is pulledin between the two bones. this can be very painful as this tissue is fully vascular andinnervated, unlike the disc. the forward dislocated disc forms an obstacle
for the condyle movement when the mouth isopening. in order to fully open the jaw, the condyle has to jump over the back end of thedisc and onto its center. this produces a clicking or popping sound. upon closing, thecondyle slides back out of the disc hence another "click" or "pop". this condition iscalled disc displacement with reduction . in later stage of disc dislocation, the condylestays behind the disc all the time, unable to get back onto the disc, the clicking sounddisappeared but mouth opening is limited. this is usually the most symptomatic stage- the jaw is said to be "locked" as it is unable to open wide. at this stage the conditionis called disc displacement without reduction fortunately, in majority of the cases, thecondition resolves by itself after some time.
this is thanks to a process called naturaladaptation of the retrodiscal tissue, which after a while becomes scar tissue and canfunctionally replace the disc. in fact, it becomes so similar to the disc that it iscalled a pseudodisc.
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