Internal derangements involve anterior displacement of the disc that acts as a cushion between the skull and lower jaw. In the early stages, the anteriorly displaced disc returns to its normal position during mouth opening and is accompanied by a clicking or popping sound. This is referred to as “anterior displacement with reduction.” In later stages, when the disc becomes more anteriorly displaced, it acts as a barrier to condylar movement and limits mouth opening. This is referred to as “anterior displacement without reduction.” It has also been referred to as “closed lock.”