I have coined two differentiations of the dimpler action: y-axis dimpler and z-axis dimpler. I have done so, because the existing FACS facial actions do not effectively encompass the depth of expression possible to achieve from the buccinator muscle (the muscle behind AU14).
There are two types of dimplers that I have observed:
1) y-axis dimpler – involving outer portions of the lip corners compressing against each other in a vertical plane
2) z-axis dimpler – involving the inner mouth portions of the lip corners pushing against the teeth and inner cheeks
AD19 - tongue show
AD = action descriptor
NOTE: Vertical lip tightener is not an official FACS shape. I have created this sub-action unit in order to further break down orbicularis oris movements. See more here.