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Figure 1. Magnetic resonance images of TMJ-internal derangement and -osteoarthrosis. Internal derangement of the TMJ is defined as an abnormal positional relationship of the disc relative to the mandibular condyle and the articular eminence, while TMJ-osteoarthrosis is characterized by structural failure of articular cartilage in the early stage and by the deterioration of the cartilage and subchondral bone, resulting in shortening of the mandibular ramus and subsequent mandibular retrusion. Both internal derangement and osteoarthrosis of the TMJ are regarded as a frequent cause of pain and/or disturbed mandibular movement. The characteristic radiographic sign of TMJ-osteoarthrosis is dysfunctional remodeling on the mandibular condyle and articular eminence surfaces with osteophyte formation. (A) At the initial stage, the disc reveals a slight anterior disc displacement but not complete displacement at the intercuspal position. At maximum mouth opening, the disc is located between the condylar and temporal bone surfaces, and the condyle and disc move harmoniously. Arrowheads indicate the anterior and posterior ends of the disc. (B) At the intercuspal position, the disc reveals anterior displacement, but not bony remodeling and deformation. On full opening, the disc reduces, usually resulting in 2 noises (reciprocal clicking). Arrowheads indicate the anterior and posterior ends of the disc. (C) Through mandibular movements, the disc is displaced from its normal position, and on full opening, the disc deformity occurs because the condyles push the disc forward and downward. In this case, bony changes on the condylar surface are not detected. Arrowheads indicate the anterior and posterior ends of the disc. (D) The disc also reveals anterior displacement without reduction, in which the disc is severely deformed on full opening. Arrowheads indicate the anterior and posterior ends of the disc. Furthermore, the osteophyte of the peripheral cortical bone, indicated by arrows, is clearly detected, indicating TMJ-osteoarthrosis. (E) The condyle shows severe bony deformation with flattening and erosion, indicating severe osteoarthrosis of the TMJ. Arrows indicate the deformed surface of the mandibular condyle. The disc also reveals anterior displacement without reduction. Arrowheads indicate the anterior and posterior ends of the disc. The individual at this stage is likely to have spontaneous joint pain and movement disability.

J DENT RES, Vol. 87, No. 4, 296-307 (2008)
DOI: 10.1177/154405910808700406

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