Disc displacement can occur with and without reduction. In a
disc displacement with reduction the disc reassumes its position
on the top of the condyle upon function of the mandible. When
that happens, it frequently generates sound (usually reported as
clicking or popping sounds). This clicking sound upon mouth
opening is called “opening click” and can happen at any time
during the movement, depending on the traction of the superior
lateral pterygoid muscle, traction of the SRL, and mainly on the
 disc–condyle morphology. However, the opening click most
 frequently happens toward the end of the condylar rotation and
beginning of the condylar translation. A second clicking sound
might be present during mouth closing. It is called “closing click”
or “reciprocal click”, and generally occurs when the teeth are
close to occlusion (intercuspal position).