Fig. 1

Normal intervertebral disc and its displacement. Normal disc-condyle relationship, the articular disc is located above the top of the condyle, as shown by the red arrow. The closed-mouth (A) and opened-mouth position (B) of normal intervertebral disc were presented. Disc displacement without reduction, the posterior zone of the articular disc lies in front of the condyle. The closed-mouth (C) and opened-mouth position (D) of disc displacement without reduction were presented. Disc displacement with reduction, the posterior zone of the articular disc lies in front of the condyle. The closed-mouth (E) and opened-mouth position (F) of disc displacement with reduction were presented