الفهرس 
? Introduction.Only 14 pages are availabe for public view
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Abstract
The most frequent cause of temporomandibular joint disorders is internal derangement. Internal derangement results from an abnormal relationship of the TMJ disc to the mandibular condyle, articular eminence, and glenoid fossa (117).
Internal derangement is considered to be a progressive disorder. In initial stages the disc is usually displaced forward when the mouth is closed and return to normal position (recaptures) on mouth opening, anterior displacement with reduction. As the elastic fibers in the bilaminer zone become stretched and lose elasticity, the disc no longer recaptures with mouth opening, anterior disc without reduction (102).
In chronic anterior disc displacement without reduction , the disc is anteriorly positioned and progressive opening of the mandible becomes deformed and compressed (2). Deformation of the disc is frequently found in non reducing conditions and the normal biconcave (bow-tie) configuration seems to change as a result of disc displacement. The more deformed the temporomandibular joint disc, the more substantial the clinical signs and symptoms (81).
Joint effusion is usually described as a large amount of articular fluid. The presence of joint effusion has been associated with TMJ disc displacement. The percentage of joints with joint effusion was greater in patients with the more advanced stages of disc displacement (disc displacement without reduction) than in those with the earlier stage (disc displacement with reduction (84).
Chronic internal derangement of TMJ may be complicated by degenerative osteoarthritic condylar changes with increased risk of bone marrow edema (114).
MR imaging has the advantage of providing detailed anatomic information involving the articulation and the surrounding structures and can be performed in closed- and open-mouth positions. This allows dynamic assessment of the disc, which is often the implicated structure in TMJ disorders (120). MRI of TMJ allows noninvasive and accurate diagnosis of TMJ disc internal derangement problems and enables a differentiation of early stages of disc displacement from more advanced and irreversible stages with osseous destruction, which could alter patient management (117).
In our study, we examined 60 joints by sagittal oblique T1, T2 and PD WI sequences in both closed and opened mouth positions.
There were 28 normally positioned discs out of the examined 60 joints. There were 13 joints showing Partial anterior disc displacement with reduction, 1 of them showed degenerated deformed disc with altered signal intensity. None of them showed effusion nor secondary changes. We found 5 joints showing partial anterior disc displacement without reduction, All of them showed deformed disc with altered signal intensity. None of them showed effusion nor secondary changes.
We found 13 joints showing complete anterior disc displacement without reduction, 11 joints of them showed deformed disc with altered signal intensity. 3 joints of them showed effusion & 5 joints showed secondary degenerative changes, Only one joint showed degenerative changes with joint effusion apart from normal positioned disc.