TMJ ARTICULAR DISC POSITION AND CONFIGURATION 30 YEARS AFTER INITIAL DIAGNOSIS OF INTERNAL DERANGEMENT

Purpose: This study evaluates disc position and configuration on magne tic resonance imaging (MRI) in temporomandibular joints (TMJs) with a long history of internal derangement. Patients and Methods: Sagittal T 1-weighted MRIs of 55 TMJs that were diagnosed with internal derangeme nt approximately 30 years ago were made with the mouth closed and open , and the position and configuration of the articular disc were determ ined. For comparison, a control group consisting of 15 asymptomatic TM Js without clinical signs of internal derangement or of other TMJ diso rders were studied in the same way. Results: Anterior disc position wa s found in 90% of the TMJs with a history of internal derangement. Red ucing disc displacement was found in one third of these TMJs, whereas permanent displacement was found in two thirds. In four joints, no dis c was discernible, In one of the joints of the control group, a perman ent disc displacement was found; normal disc position was found in all other joints of the control group. A biconcave disc configuration, wh ich was considered normal, was found only in TMJs with normal disc pos ition or with reducing discs. Conclusion: It was concluded that, after 30 years of displacement, the TMJ disc can be clearly identified on M RI in most cases. If the disc becomes permanently displaced, its confi guration deviates from the normal biconcave configuration, and its ant eroposterior length decreases, Convex and folded appearances of the di sc are common in this situation, However, the disc usually maintains i ts biconcave configuration as long as it resumes its position on top o f the condyle during mouth opening, even if this condition lasts for s everal decades.