Editing Temporomandibular joint dysfunction (section)

===Disc displacement===
In people with TMD, it has been shown that the lower head of [[Lateral pterygoid muscle|lateral pterygoid]] contracts during mouth closing (when it should relax), and is often tender to palpation.<!-- <ref name="Scully 2008" /> --> To theorize upon this observation, some have suggested that due to a tear in the back of the joint capsule, the articular disc may be displaced forwards (anterior disc displacement), stopping the upper head of lateral pterygoid from acting to stabilize the disc as it would do normally.<!-- <ref name="Scully 2008" /> --> As a biologic compensatory mechanism, the lower head tries to fill this role, hence the abnormal muscle activity during mouth closure.<!-- <ref name="Scully 2008" /> --> There is some evidence that anterior disc displacement is present in a proportion of TMD cases.<!-- <ref name="Scully 2008" /> --> Anterior disc displacement with reduction refers to abnormal forward movement of the disc during opening which reduces upon closing.<!-- <ref name="Scully 2008" /> --> Anterior disc displacement without reduction refers to an abnormal forward, bunched-up position of the articular disc which does not reduce.<!-- <ref name="Scully 2008" /> --> In this latter scenario, the disc is not intermediary between the condyle and the articular fossa as it should be, and hence the articular surfaces of the bones themselves are exposed to a greater degree of wear (which may predispose to osteoarthritis in later life).<ref name="Scully 2008" />