Smile
The zygomatic major muscle is embedded inside the midfacial SMAS. Having filler material inside the fibrous layers may result in the limited ability of the muscle to pull the modiolus and thus the oral commissure vertical and horizontal toward the zygomatic arch; this seems to lead in the patient’s perception of an unnatural smile.
Study the first image to recognize the different layers. If you are sure about the layers, swipe to the second image to view the answer (if applicable).